MON HOC: THC HANH PHAN TCH CAC CH TIEU MOI TRNG

CHNG I :

I CNG V PHNG PHP PHN TCH HA L1.1. ai cng

Bn cnh cc phng php phn tch ha hc, phng php phn tch ha l da trn tnh cht vt l v ha hc ca vt cht, kho st hin tng xy ra khi vt cht chu tc ng ca nhng yu t: bc x, in, nhit. Kt qu tng tc c ghi nhn, t c th nh tnh hay nh lng mu vt cht. to s tc ng v ghi nhn kt qu tng tc, cn dng c v thit b thch hp, do phng php cn c c gi l phng php phn tch cng c.

Hin nay, cc thit b dng trong phn tch cng c pht trin v hin i ha, do cng m rng phng php v tn ng dng nhng thit b ny.

So vi cc phng php phn tch ha hc, nhng phng php phn tch ha l c u im:

nhy cao, c th nh lng n nng vi ppm hay c th vi ppb.

C chnh xc cao, lp li cao. C tnh chn lc, c th xc nh ng thi nhiu cu t m khng qua giai on tch chng

Nhanh, vi h thng t ng c th xc nh hng lot mu

Nhc im:

Cn thit b v chuyn vin vn hnh, bo tr . Thit b t tin

1.2. Phan loai

Ty thuc bn cht ca hin tng gy tc ng v ty thuc thit b s dng c th chia lm 4 nhm phng php chnh.

1.2.1. Nhom cac phng phap quang

Nguyn tc da trn s tng tc gia mu v bc x. Ty bn cht ca mu v bc x, thu c kt qu di dng tn hiu hay i lng o, t nh tnh v nh lng mu.

Nhng phng php thng dng gm :

Phng php quang ph hp thu: t ngoi, thy c, hng ngoi, cng hng t ht nhn.

Phng php quang ph pht x

Phng php quang ph ngn la: hp thu v pht x

1.2.2. Nhom cac phng phap ien hoa

Da trn hin tng lin quan n tnh cht in ca mu kho st, hay da trn tnh bin thin ca mt s i lng vt l ca dng in khi c s hin din ca mu trong h thng mch.

Gm:

Phng php in khi lng

Phng php chun in th

Phng php cc ph v chun ampe

Phng php o in dn

1.2.3. Nhom cac phng phap sac kyDa trn tnh cht phn b hay hp ph khc nhau ca nhng cu t trong mu gia hai dung mi hay hai pha ng khng trn ln vo nhau, c th tch ri nhng cu t trong mu nh tnh v nh lng chng .

Cc phng php sc k n gin

Sc k kh : lng kh v rn kh Sc k lng: lng lng v rn lng 1.2.4. Nhom cac phng phap khac

Gm nhng phng php khc khng thuc 3 nhm trn:

Phng php phn tch nhit

Phng php phn tch nhit in

Phng phn o dn in

Phng php chun nhit lngCHNG II: I CNG CC PHNG PHP PHN TCH QUANG PH

2.1 Khi nim v phng php quang ph

Phng php quang ph hc l phng php nghin cu s tng tc in t cc loi bc x khc nhau ca vi vt cht. Cc bc x tng tc vi vt cht nh th no l ty thuc vo nng lng ca n. V d cc tia cc tm, tia kh kin c nng lng cao nh hng ti cc mc nng lng ca cc electron bn ngoi. Bc x hng ngoi c hp th bi vt cht dn n s quay hay dao ng ca cc phn t. Ngoi ra khi vt cht hp th nng lng t cc ngun khc nh nng lng nhit, nng lng in chng s chuyn ln trng thi cao hn. trng thi ny chng khng bn v pht ra nhng bc x c trng tr v trng thi c bn. V vy trong phng php quang ph nu phn loi theo hin tng ta c phng php ph hp th v phng php ph pht x. Nu phn loi theo bn cht sng in t ta c ph IR, ph UV-Vis, ph tia X v.v.... Trong phng php quang ph cc cht c nhn bit thng qua tn s hay bc sng t trng t qu trnh hp thu hay pht x v c nh lng thng qua lng bc x in t c hp th hay pht x, Vn ny s c lm sng t trong cc chng tip theo

2.2 Sng in t

2.2.1 Tnh cht sng in t

a. Mt s quan nim v bc x in t

Thuyt v sng in t do Maxwell a ra. Theo ng th mi bin thin ca in trng u lm pht sinh ra mt t trng v ngc li, mi bin thin ca t trng u lm xut hin mt in trng trong khng gian xung quanh.

V vy khi mt in tch dao ng vi tn s

s lm xut hin mt in trng v mt t trng bin thin cng tn s . Trng tng hp ca in trng v t trng gi l trng in t. Trng in t truyn trong khng gian gi l sng in t

Chnh Maxwell, ngi u tin tin on sng in t vi tn s thch hp phi ng nht vi nh sng nhn thy. iu c ngha l nh sng c bn cht l sng in t. L thuyt ny gi thuyt sng in t .

Trong sng in t, in trng v t trng lun lun c phng vung gc vi nhau v gc vi phng truyn ca sng in t ( ti mi im cng in trng v cng t trng tng ri gim v i chiu

Qung ng m sng in t truyn i trong mt chu k T ( thi gian thc hin mt dao ng ) c gi l bc sng hay di sng . Nu gi c l vn tc truyn sng ta c h thc: = c.T= c/ ( l s chu k trong mt giy)

Sng radio, vi sng, bc x hng ngoi ( IR), nh sng thy c ( kh kin vis) , bc x t ngoi( UV) tia rngen (X), tia u l sng in t. Bn cht ca chng ging nhau ch khc nhau di sng .

Trong ph sng in t c mt vng hp t 390nm < < 770nm c th thu nhn c bng mt gi l bc x kh kin.

Min kh kin chia lm 7 vng hp vi mu sc khc nhau. Nu i t vng bc sng di ti vng bc sng ngn ta c cc min : , cam, vng, lc, cam, vng, tm

Ni tip vi min tm v pha bc sng ngn l vng t ngoi (UV). Tia v tia rngen (X) l nhng bc x in t c bc sng ngn.

Ni tip vi vi min vng bc sng di l min bc x hng ngoi (IR) , tip theo l min vi sng v sng radio ( i truyn thanh)

Thuyt lng t ca Planck (1900)

Mt vt rn khi c t nng s pht ra bc x, ph thu c gi l ph bc x nhit. Bc x nhit pht ra l do chuyn ng dao ng ca cc ht tch in c th l ion, electron cc vt th c t nng. gii thch ph bc x nhit nm 1900 Planck a ra thuyt lng t gi l thuyt lng t Planck

Theo thuyt lng t th Mt dao ng t dao ng vi tn s ch c th pht ra hay hp thu nng lng tng n v gin on, tng lng nh mt, nguyn vn, gi l nng lng lng t , lng t nng lng ny t l vi tn s ca dao ng t

= h

h l hng s Planck , h = 6,625.10-34j.s

Thuyt Planck nh vy pht hin ra tnh gin on ca nng lng. Gi l tnh lng t.

Mt khc, v nng lng ca dao ng t pht ra hay hp thu di dng nng lng bc x nn thuyt lng t Planck cng c ngha l: nh sng hay bc x ni chung gm nhng lng t nng lng = h pht i t ngun sng.

V vy thuyt lng t Planck cn gi l thuyt lng t nh sng

Tnh nh nguyn sng ht ca nh sng

Theo thuyt lng t nh sng th nh sng gm nhng lng t c nng lng = h pht ra t ngun sng. Mc khc theo h thc tng i Eintein (1903) E = mc2 th vt th bt k nu c nng lng l E th s c khi lng m = E/ c2. Nh vy ng vi nng lng lng t = h th nh sng c khi lng:

T ta c tnh ht ca nh sng.

Thuyt lng t nh sng c Planck a ra nm 1900 v tnh ht nh sng c suy ra mt cch t nhin t h thc tng i ca Eintein. Thuyt lng t hay thuyt ht nh sng ch l mt v do s pht minh ng gp ca hai nh bc hc li lc l Planck v Eintein

Theo h thc tng i Eintein : hay

i vi chnh nh sng th v = c suy ra : m0 = 0 vy khi lng ngh m0 ca nh sng bng khng.

Theo thuyt lng t nh sng th mu sc ph thuc vo nng lng ca photon( lng t nh sng ) = h = h, ngha l ph thuc vo tn s nh sng cn cng nh sng ph thuc vo nng ht nh sng trong chm sng.

Tnh nh nguyn ca nh sng

Trc khi c thuyt ht nh sng c thuyt sng nh sng do Maxwell a ra 1865. N gii thch c cc hin tng nh giao thoa nh sng, nhiu x nh sng nhng khng gii thch c cc hiu ng quang in Ngc li thuyt ht gii thch c cc hiu ng quang in nhng khng gii thch c cc hin tng nh giao thoa nh sng.

Lch s khoa hc ghi nhn trong thi k ny c cuc tranh ci gia hai trng phi sng v ht. Nhng ngi theo trng phi sng th c gii thch nhng hin tng nh hiu ng quang in, cn nhng ngi theo trng phi ht th c gng gii thch cc hin tng nh giao thoa nh sng.

Nm 1924 Louis de Broglie mt nh bc hc ngi Php thng nht hai thuyt. Theo ng chnh thuyt ht v nh sng tha nhn tnh sng, v theo thuyt ny, ht nh sng c nng lng c tnh theo cng thc , trong c cha tn s , mt i lng c trng cho bn cht sng, v vy theo ng khng th n thun coi nh sng l ht m cn tha nhn tnh sng ca nh sng. iu c ngha l nh sng va c tnh sng va c tnh ht. Ngi ta ni nh sng c tnh nh nguyn sng- ht

2.2.2 Cc i lng biu din sng in t v biu thc lin quan gia cc i lng

- di sng (: Khong cch gia hai cc i hay hai cc tiu k tip nhau. n v l cm, nm, (m,

- Chu k T : thi gian sng truyn t cc i ny sang cc i k tip. n v l giy

- Tn s (: s dao ng trong mt giy. n v ( = 1/T

- Tc truyn sng trong chn khng

C = (. (= 3.1010 cm/s

- S sng = 1/( ( cm-1 ) m t s sng thc hin c trong mt giy

2.3 Nng lng ca vt cht v tng tc sng in t ti vt cht

2.3.1 Nng lng ca vt cht

Theo l thuyt caAlbert Einsteinmi vt c khi lng u c nng lng, do cng c th ni mi dng thc th ca vt cht trong t nhin u c nng lng. Nng lng ca vt cht ph thuc vo khi lng ca n. Nu mt vt c khi lng lmth n c nng lng tng ng lE=mc. Trongphn ng ht nhn, nu khi lng thay i mt lng lmth nng lng cng thay i mt lng tng ng lE. Phn nng lng thay iEc th l ta ra hay thu vo. Nu l ta ra th tn ti di dng nng lng nhit vbc xra cc ht c bn. S phn b nng lng trong phn t ca mt cht bao gm ba trng thi: Trng thi in t- trng thi Dao ng v trng thi Quay. Nh vy nng lng bn trong phn t l tng cc dng nng lng : E = Eel + Ed + EqEel : l nng lng in t ph thuc vo s phn b in t. Bin thin ca n ph thuc vo s chuyn in t t orbital phn t ny sang orbital phn t khc.

Ed : l nng lng dao ng , c trng cho s dao ng ca cc ht nhn nguyn t xung quanh v tr cn bng ca chng trong phn t

Eq : l nng lng quay, lin quan ti s quay ca phn t xung quanh nhng trc no trong phn t

2.3.2. Tng tc sng in t vi vt cht

Khi chiu bc x in t vo dung dch cha cc phn t th bc x in t c th b khuych tn hoc b hp thu. Ph phn t chnh l ghi li s hp thu bc x bi phn t.

Khi phn t hp thu bc x, chuyn t trng thi c bn ln trng kch thch, ngha l bn thn n thay i mc nng lng E = Ekt Ecb = Eel +E d+ EqV : Eel > E d> Eq

Cc trng thi nng lng ca phn t gm hai nguyn t

Cc mc nng lng quay J rt gn nhau, cc mc nng lng dao ng v xa nhau hn, cn cc mc nng lng in t th cn xa nhau hn na. Mi mt trng thi in t bao gm cc trng thi dao ng khc nhau, v mi trng thi dao ng n lt n bao gm cc trng quay khc nhau. V th nhng chuyn mc nng lng in t thng km theo s bin thin nng lng dao ng v c nng lng quay .

Nhng phn t c nhiu nguyn t s c nhiu chuyn mc nng lng khc nhau m mi loi chuyn mc cng c th c biu din bng s nh trn.

nhit khng tuyt i, lp v in t ca phn t khng b kch thch , s quay ca phn t s khng xy ra , nhng phn t vn c mt nng lng dao ng no gi l nng lng dao ng im 0. Khi tng dn d tr nng lng nhit ca phn t n gi tr 0,03- 0,3 Kcal/mol, trng thi quay ca phn t bt u b kch thch nhng trng thi dao ng v trng thi in t vn khng i.

Khi nng lng chuyn ng nhit tng ln 0,3- 12Kcal/mol, trng thi in t ca phn t cng cha b kch thch nhng trng thi dao ng bt u b kch thch . Nhng photon tng ng vi bin thin nng lng dao ng c bc sng vo c: = 2500nm- 0,1mm ng vi bc x vng hng ngoi.

Mun kch thch cc in t th cn phi dng nng lng cao hn, vo khong vi chc n vi trm Kcal/mol . Nng lng ng vi vng kh kin v t ngoi.

Cc bc x c nng lng thp nh sng cc ngn hoc hng ngoi xa ta s thu c ph quay thun ty. Ph thun ty bao gm nhng vch ph cch u nhau v gn nhau, mi vch c tn s:

Khi phn t b kch thch vng hng ngoi gn, trng thi dao ng b kch thch nhng lng t nng lng ng vi tn s :

Cui cng khi phn t hp thu bc x c nng lng ln nh bc x kh kin hay t ngoi th nng lng in t ca chng thay i. Nu trng thi in t b thay i th vch hp thu tng ng s c tn s :

Nh vy khi trng thi in t ca phn t thay i, nhng trng thi dao ng v quay cng thay i ng thi, ta thu c ph electron- dao ng- quay m thng ch gi l ph electron ca phn t v so vi s thay i ca trng thi dao ng v trng thi quay th trng thi in t qu ln.

Thc ra mi vch ring ca ph clectron c tn s cho bi biu thc:

= el + d + qi lng el c xc nh bi bin thin nng lng in t ca phn t. Thng el > d vi chc ln v ln hn q vi nghn ln

Nn: el . V vy khi s hp thu bc x c nh hng ti trng thi in t th ph thu c xem nh ph in t

Vt hp thu dng nguyn t hay phn t ta c ph hp thu nguyn t hay phn t tng ng

- Tn s bc x b hp thu c ngha c trng c cu trc vt cht . Nghin cu tn s (bc sng) hp thu trn ph nhn din hay nh tnh mu. Da vo ph hp thu c th nh lng mu.

2.3.3 Cc loi ph hp th

Ph hp th phn t UV- Vis

Cc cht hp th l cc phn t, c kh nng hp th cc bc x in t trong vng UV-Vis. Do nng lng ca bc x trong vng nay tng i ln, nn chng kch cc in cc lin kt hay cc in t t do, dn ti ph hp thu. Trong ph hp th UV-Vis cc nhm chc khc nhau s hp th cc bc sng cc nhau. V vy dng ph UV-Vis c th d on s c mt ca cc nhm. Ph thu c cho qu trnh ny l nhng mi hp th ni tip nhau, nn c gi l ph m.

V mt nh lng c th dng ph UV-Vis nh cc cht thng qua nh lut Lambert- Beer

Hnh trn l ph hp thu ca phn t Benzen 2 trng thi lng (a) v hi (b)

Ph hp thu nguyn t

Cc cht hp th cc nguyn t kim loi trng thi hi. trng thi ny chng c kh nng hp th nhng bc x in t t trng trong vng t ngoi, gy ra ph hp th nguyn t. Ph thu c cho qu trnh ny l nhng vch ph t trng, nn c gi l ph vch. Nhng nguyn t kim loi khc nhau trng thi hi nguyn t c kh nng hp th nhng bc x in t c bc sng khc nhau. Chnh v vy, ngi ta c th da trn bc sng b hp th d on s c mt ca kim loi . V mt nh lng cng da trn ng dng nh lut Lambert- Beer.

Hnh trn l vch ph hp thu ca nguyn t As, bao gm hai vch 197,2nm c nhy cao v 193,7nm c d nhy thp hn

Ph Hng ngoi

L ph hp thu trong cc phn t hp th bc sng nh sng tng ng vi trong vng IR. Phng php phn tch theo ph hng ngoi l mt trong nhng k thut phn tch rt hiu qu. Mt trong nhng u im quan trng nht ca phng php ph hng ngoi vt hn nhng phng php phn tch cu trc khc (nhiu x tia X, cng hng t in t vv) l phng php ny cung cp thng tin v cu trc phn t nhanh, khng i hicc phng php tnh ton phc tp. K thut ny da trn hiu ng n gin l: cc hp chp ho hc c kh nng hp th chn lc bc x hng ngoi. Sau khi hp th cc bc x hng ngoi, cc phn t ca cc hp cht ho hc dao ng vi nhiu vn tc dao ng v xut hin di ph hp th gi l ph hp th bc x hng ngoi. Cc m ph khc nhau c mt trong ph hng ngoi tng ng vi cc nhm chc c trng v cc lin kt c trong phn t hp cht ho hc. Bi vy ph hng ngoi ca mt hp cht ho hc coi nh "du vn tay", c th cn c vo nhn dng chng.Trong ph hng ngoi ngi ta chia lm 3 vng da trn bc sng ca chng:

1- Cn hng ngoi ( near infrared) = 0,8 2,5m

2- Trung hng ngoi ( medium infrared) = 2,5 50m

3- Vin hng ngoi ( far infrared) = 50 - 100m

* Trong vng hng ngoi gn (NIR):

T 12500 cm-1 tri di n khong 4000 cm-1 c rt nhiu m ph c lin quan n nguyn t H. Trong s , dao ng co gin (bi) ca O - H gn 7140 cm-1 v N-H gn 6667 cm-1, m ph t hp do cc dao ng co gin v dao ng bin dng ca C-H ca nhm ankyl 1548 cm-1 v 3856 cm-1.

hp th ca m ph NIR thp hn t 10 n 1000 ln so vi cc m ph vng hng ngoi gia.

Vng NIR c th ghi c vi h quang hc thch anh, kt ni vi cc detect nhy vi NIR v ngun bc x mnh hn.

* Vng hng ngoi gia:

tm c rt nhiu tng quan b ch trong vng hng ngoi gia.Vng ny c chia thnh min "tn s nhm" 4000 1300 cm-1 v vng"du vn tay" 1300 - 650 cm-1.Trong khong 4000 2500 cm-1 s hp th c trng cho dao ng co gin ca H vi cc nguyn t khi lng < 19.

Phn ch yu trong ph gia 1300 v 650 cm-1, l cc tn s co gin ca lin kt n v tn s cc dao ng un (cc tn s b khung) ca h nhiu nguyn t. l vng "nhn dng" "(vng "du vn tay"). Vng ph ny ht sc a dng , kh cho vic nhn bit ring r cc m ph mt cch chc chn, nhng kt hp cc m ph hp th, gip cho vic nhn bit cc cht.

* Vng hng ngoi xa:

Vng 667 - 10cm-1 bao gm cc dao ng bin dng ca C, N, O, F vi cc nguyn t khi lng > 19 v cc dao ng bin dng trong h thng mch vng hoc cha no. Vng dao ng tn s thp trong ph hng ngoi rt nhy i vi s thay i cu trc phn t, bi vy m ph vng hng ngoi xa thng cho php d on cc dng ng phn. Ngoi ra, vng ny c bit tt cho vic nghin cu cc c kim v cc hp cht v c c cc nguyn t nng v lin kt yu.

Trn y ta thy c s lin quan gia cu trc phn t v s xut hin cc m ph dao ng (ph hp th hng ngoi).

Tn s dao ng ca nhm nguyn t no trong phn t t ph thuc cc phn cn li ca phn t c gi l tn s c trng cho nhm .

Khi ni tn s c trng ca nhm khng thay i th khng c ngha l max hp th l khng i m ch c ngha l max nm trong mt min ph kh hp. V d lin kt C-H c tn s c trng trong khong 2800 2900 cm-1

2.4. S pht x v cc loi ph pht x

2.4.1. . S pht x ca vt cht

Vt cht dng nguyn t hay phn t , nhn nng lng bc x thch hp, chuyn mc nng lng thp (bn) ln mc nng lng cao hn (km bn ), c khuynh hng tr li mc nng lng thp hn v c th pht ra bc x, l hin tng pht x.

d tm hiu qu trnh pht x chng ta xt gin nng lng v ph pht x ca nguyn t Hydro

Cc trng thi nng lng ca e trong nguyn t H

Nng lng ca e tnh c khi gii phng trnh Schroedinger:

Ta thy nng lng ca cc e ph thuc vo s lng t chnh n (lp)

- Vi n = 1 ( lp K )ta c E1= -13,6ev ng vi trng thi c bn

- Vi n = 2 ( lp L )ta c E2= -3,4ev

- Vi n = 3 ( lp M )ta c E3= -1,51ev

Gin nng lng v s xut hin cc dy ph pht x hydro

Dy Lyman : tp hp cc dy ph ng vi nhng bc chuyn e t nhng mc nng lng cao ( lp ngoi nc 2) v mc c bn (nt=1) to nn dy vch gi l dy Lyman do ng tm ra vo nm 1916.

Nh vy i vi dy Lyman th nc = 2,3,4. v nt =1

V hiu cc mc nng lng ln nn nhng bc x trong vng ny c bc sng ngn ( = h) thuc min t ngoi

Dy Balmer: Nhng vch ph thu c do su chuyn ng e t cc lp bn ngoi ( nc 3) v lp nt =2 to dy Balmer. Bc sng ca cc bc x pht ra trong dy Balmer thuc vng kh kin c th quan st bng mt, y l dy ph quan trng c Balmer tm ra vo nm 1885.

Di y l nhng vch ph thuc dy Balmer thng gp

H mu : nc = 3, nt = 2 v = 656nm

H mu lam : nc = 4, nt = 2 v = 486nm

H mu tm : nc = 5, nt = 2 v = 434nm

Dy Paschen: Nhng vch ph thu c do s chuyn e t cc lp c nc 4 v lp nt=3 to thnh dy Paschen. Nhng bc x trong vng ny thuc vng hng ngoi c bc sng c 1000nm 770nm

S pht x ca hai nguyn t Na v hydro

2.4.2. Cc loi ph pht x

Ph pht x nguyn t

Ph thu c t s pht x ca cc nguyn t trng thi hi ang trng thi kch thch. L mt phng php phn tch vt l da trn tnh ch t pht x ca nguyn t trng thi hi xc nh thnh ph n ha hc ca cc nguyn t, cc cht trong mu phn tch. Phng php ny c s dng phn tch nh tnh v nh lng cc nguyn t ha hc, ch yu l cc kim loi trong mi i tng mu khc nhau, nh a cht, ha hc, luyn kim, ha du,

nng nghip, thc phm, y dc, mi trng... thuc cc loi mu rn, mu dung dch, mu bt, mu qung, mu kh. Trong phng php ny cn thit phi c ngun nng lng p ng cho qu trnh ha hi, nguyn t ha v kch thch cc nguyn t ca cc nguyn t ln trng thi kch thch, trng thi kch chng khng bn v pht ra nhng bc x c trng. Cc nguyn t kim loi khc nhau s pht ra nhng bc x khc nhau, c bc sng xc nh. Phn tch nh tnh s da trn bc sng t trng, phn tch nh lng da trn cng vch pht x.

Ph pht x ion

Nguyn tc: Trong quang ph pht x (OES), mu c t nhit cao gy ra khng ch phn ly thnh cc nguyn t m cn ion ha cc nguyn t. Khi cc nguyn t hoc ion trng thi kch thch c th phn hy v mc nng lng thp hn thng qua qu trnh chuyn di nng lng v pht x. Trong OES, cng nh sng pht ra cc bc sng c th c o v c s dng xc nh nng ca cc kim loi. Gn y vic p dng k thut plasma vo phn tch OES mang li tim nng ln.

My quang ph ICP-OESKh Argon c dn qua mt ngn la gm ba ng ng tm lm bng thch anh, mt cun dy ng, gi l cc cun dy ti, bao quanh cui cng ca ngn la v c kt ni vi my pht tn s (RF).Nng lng RF (thng l 700-1500 watt) c duy tr trong cun dy vi t l tng ng vi tn s ca my pht in. Trong hu ht cc thit b ca ICP tn s ny l 27 hoc 40 megahertz (MHz). Dng in trong cun dy gy ra in trng v t trng c thit lp trong khu vc trn cng ca ngn la. Vi kh argon c i qua b phn t, tia la in c nh vo dng kh gy ra hin tng mt s electron b vng ra t nguyn t argon. Nhng electron ny sau b cun vo t trng v gia tc. Cc electron nng lng cao ln lt va chm vi cc nguyn t argon gy ra s ion ha. S Ion ha ny tip tc trong mt phn ng dy chuyn, ph v kh thnh mt plasma bao gm argon nguyn t, in t, v argon ion.

Hnh 2.9. Bng gii hn pht hin ICP-OES

Hnh 2.10. Mt ct ngang ca mt ngn uc ICP v cc cun dy ti m t mt chui nh la.

A Kh Argon l xoay qua ngn uc. B Nng lng RF c p dng cho cc cun dy ti.

C Mt tia la to ra mt s electron t do trong argon. D Cc in t c gia tc bi in trng gy ion ha vto thnh mt plasma. E Mu c phun vo ngn.

Hu ht cc mu dng lng c a vo mt bnh phun sng m v a vo trung tm ca plasma. u tin nhit trong ngn uc s loi b cc dung mi. Cc bc tip theo lin quan n vic phn hy v sau in ly thnh cc nguyn t. Cc qu trnh ny xy ra ch yu khu vc sy s b (PHZ), plasma c chc nng kch thch v ion ha. Cc kch thch v ion ha cc quy trnh xy ra ch yu trong vng bc x ban u (IRZ) v phn tch thng thng khu vc (Naz).

Mu c vn chuyn vo thit b thnh mt dng cht lng v c chuyn thnh dng sng thng qua mt b phn c gi l bnh phun. Mu c phun dng sng sau c vn chuyn n bung t, ti y c ui ht dung mi, bay hi, v ion ha. Cc nguyn t c kch thch v pht ra bc x ion c trng ca n v c thu thp bi mt thit b c bit. Bc x c pht hin v bin thnh tn hiu in t

Hnh 2.13. Cc thit b chnh v b tr ca mt thit b ICP-OES in hnh.2.5. Cc chi tit trong my quang ph

2.5.1 Thit k c bn trong thit b quang ph

Thit k c bn trong my quang ph bao gm 5 b phn chnh:

Da vo nguyn tc ca phng php trong my o quang c cc b phn chnh nh sau :

5

Trong :

1. Ngun bc x tn hiu

2. B phn to n sc

3. Mu

4. B phn nhn kt qu v chuyn thnh tn hiu

5. My o hay my ghi

2.5.2. Ngun bc x

Da vo bn cht ca qu trnh to ra bc x m ngi ta chia lm hai loi ngun bc x: Ngui bc x lin tc v ngun bc x khng lin tc

+ Ngun bc x lin tc.

Ngun bc x lin tc l ngun pht ra di cc bc x lin tc c di sng khc nhau, sau cc bc x ny i qua b phn to bc x n sc c bc x n sc trc khi i n mu

Ty vo di sng ca bc x cn pht ra , ngi ta dng cc loi ngun sau :

- Ngun t ngoi : gm c n hydro ( cha kh H2) v n deterium ( cha kh D2)

Cu to n :

Hot ng ca n : Th cao 2000 6000v p c vo hai in cc nhm , kch thch phn t bn trong, chuyn chng t trng thi nn( trng thi c bn) ln trng thi kch thch , khi cc phn t kh b kch thch khng bn pht ra nng lng di dng nhng bc x c bc sng xc nh tr v trng thi c bn, qu trnh xy ra lin tc nh vy v ta c nhng bc x cn thit. Vi loi n ny bc xa pht ra c = 180 375nm

- Ngun n thy c : pht ra nhng bc x thy c

Cu to n :

Hot ng : Ngi ta p t th khong 6 V vi cng dng ln , t nng dy tungsten. Dy ny chy v a kh tr trong n ln trng thi kch thch t pht ra bc x c =320 2500nm. Nhit n khong 30000K.

- Ngun n hng ngoi :

Gm 3 loi n :

*Nernst: cu to bi oxyt t him l nhng nguyn t Lantanic v Actinic , dng hnh tr , chiu di 20mm. ng knh 1- 2mm

*Globar: Thanh silicol carbide mt hl kim ca Si- C , di 50cm, ng knh 0,5cm

*Dy xon nichrom ( mt hp kim c lm t Ni-Cr)

Thng dng nht l dy xon Nichrome

Hot ng ca n : Ap t th thch hp to dng in chy qua lm dy nichrome nng pht ra nhng bc x hng ngoi . Nhit n khong 20000K.

+ Ngun bc x khng lin tc

Ngun bc x khng lin tc l ngun bc x pht ra c di sng nht nh

n catot lm : hollow cathode tube

Cu to n:

Cathode: lm bng kim loi tinh kit cng nguyn t vi cu t kho st ngha l nu nh ta kho st nh lng Cu th ta dng n c cc catot l Cu .

Anode: Dy tungsteng

Hot ng n : Ap th thch hp gia hai in cc , ion ho kh bn trong , do s di chuyn cc ion n in cc lm to ra dng in gia hai in cc. Nu th p t ln , cc cation khi ng nng s p mnh vo bng cc catot l bc cc nguyn t kim loi catot ra khi in cc ny , to m my nguyn t , dng nguyn t n hp th nng lng chuyn ln trng thi kch thch khng bn v pht ra nhng bc x c bc sng xc nh tr v trng thi c bn ban u.

V d ; cu to n c catot lm bng Pb khi bc x pht ra do nguyn t Pb b kch thch c = 283nm.

2.5.3.B phn to bc sng n sc.

+ Knh lc : thng s dng loi lnh lc hp thu.

Cu to : knh lc c th l

Knh lm bng thy tinh mu

Knh lm bng phm mu dng huyn ph trn vi gelatin p gia hai bn thy tinh.

t im:

n gin r tin

Ch o hp thu nhng bc x c nh

Nng sut truyn yu

Khng to ra bc x n sc , ch truyn qua dy bc x (30-50) nm

V d : Knh lc 470nm theo l thuyt th ch c bc x c = 470nm nhng thc t th nhng bc x c = 470 30 nm cng i qua .

+ My bit sc : monochromator

Cu to : H thng gm cc khe, knh lc v b phn tn sc

Hot ng :

nh sng t khe vo, qua knh phn k n b phn tn sc , Bc s khuych tn qua thu knh hi t n mt b mt c khe ra . Bc x c di sng mong mun s i ra khe do s quay ca b phn tn sc .

B phn tn sc ( Dispersing element)

Gm 2 loi : Lng knh ( prism) v cch t ( grating)

S tn x di tc dng ca lng knh

Lng knh : C cu to ph hp cho php truyn bc x vo vng ph m ta kho st .

V d:

+ c vng bc x t ngoi dng lng knh thch anh (quartz)

+ Vng bc xthy c dng lng knh thy tinh hay thch anh.

+ Vng hng ngoi dng lng knh trong c cha mui halogenua ca kim loi kim nh KBr hay NaCl

Cch t : C hai loi l cch t truyn sut v cch t phn x

Cch t truyn sut : Transmission grating.

Cu to : Bn thy tinh trn c khc cc vch song song u nhau, c th vi trm vch trn 1cm.

Hot ng : Khi bc x chiu n cch t truyn sut , mi vch ng vai tr nh mt ngun sng mi , c hin tng giao thoa gia cc bc x , kt qu l c theo cc di sng .

Cch t phn x:

Cu to : bn kim loi bng nhm c khc cch vch .

Hot ng : Do khong ng i ca bc x n b mt cch t l khc nhau , to tia phn x gy ra hin tng giao thoa , kt qu l c s phn tch cc bc x theo cc di sng.

t im :

- Khc phc c cc nhc im ca knh lc .

Cch t c n sc cao : 0,1nm

o cc di sng khc nhau

Nng sut truyn sut khng i

To c bc sng tht n sc

C cu to phc tp v rt t tin

2.5.4.B phn cha mu: ( Sample container)

+ Cu to : B phn cha mu lm bng vt liu ng nht , cho php truyn qua bc x trong vng kho st

+ Hnh dng : Hnh khi ch nht hay ng nghim

+ Kch thc : Khong cch bn trong gia hai thnh hay ng knh thay i t 0,05mm 5 cm

+ Lu : Trnh cc vt bn , du bm ln thnh b phn cha mu

2.5.5. B phn nhn kt qu v chuyn thnh tn hiu: ( Detector)

Nguyn tc : Nhn nng lng ca bc x ra khi mu v chuyn thnh dng nng lng khc c ghi nhn bng tn hiu.

Phn loi : chia lm hai loi

+ Hiu ng quang in : Nhn quang nng ca bc x ra khi mu v chuyn thnh tn hiu in . S dng t bo quang in dng cho bc x vng t ngoi v vng thy c .

+ Hiu ng nhit in : Nhn nhit nng ca bc x ra khi mu v chuyn thnh tn hiu in . Thng s dng cp nhit in , t bo Golay , balometer. Da trn s thay i nhit lm thay i in tr ca chng , do lm thay i in th v ghi nhn s thay i di dng tn hiu in . Dng cho bc x hng ngoi v bc x ny c nng lng nh nn ch ghi nhn d thay i nhit trc v sau khi qua mu.

2.2.5. My o v my ghi :

Tn hiu nhn c t detector c ghi di dng ng biu din trn my ghi hay chuyn thnh i lng o trn my o. Ngy nay ta thy c c mng hnh vi tnh km theo my ghiCHNG III

PHNG PHP PH HP THU T NGOI V KH KIN

S tng tc bc x ca trng in t n vt cht trong vng bt u bc x t ngoi n hng ngoi, c bc sng : 180nm- 1100nm, c nghin cu k. Vng ph in t ny c gi l t ngoi v kh kin, v n cha nhng bc x pht ra m mt con ngi c th thy c, n gii thch c cu trc ca phn t v s hin din ca trng thi khng bo ha trong phn t. N tht s quan trng trong phn tch nh lng.Tnh ton hp thu bc x t ngoi v kh kin bng cch p dng nh lut LamBert- Beer l nn tng ca phng php ( nh phng php o quang). Phng php rt hu hiu trong phng th nghim trong qu trnh nh lng hm lng mu. Phng php ny khng ch p dng cho nhng hp cht c kh nng hp thu bc x trong vng ny m cn cho tt c cc hp cht c kh nng hp thu.

Trong phm vi lin quan ti phn tch k c nhng dng c t nhng thit b n gin nh my so mu n nhng my o quang ph t ng n phn tch nhiu thnh phn cu t trong hp cht. Phng php sc k lng v in di mao qun pht trin hn nh vic p dng nhn bit bng cc loi detector UV-VIS. Nhng detector ny to nn nhng sc k .

3.1. Nhng khi nim c bn

Dy ph thu c t qu trnh tng tc c th phn chia thnh 3 vng: Cn t ngoi- kh kin v vng hng ngoi gn ( ln lt t : 185- 400, 400- 700, 700- 1100nm). Hu ht cc my o u o trong vng bc sng t 185- 900nm. S hp thu bc x trong vng bt u c = 185nm l gii hn lm vic trong vng bc sng thp. Khong bc x thp hn 10-20nm l vng bc x t ngoi chn khng gi l vng t ngoi xa.

Nhng dng c ny cho php ph nhn c biu din hp thu theo bc sng. Bc sng c tnh theo n v nm v c xem l n v biu din trong ph .

Hnh trn l ph khc nhau trong vng ph kh kin v t ngoi

Hnh a: Ph thu c trong trng hp hp cht trng thi dung dch ( Hu ht l trng hp ny )

Hnh b: Ph c cu trc p d nhn bit

Hnh c: Ph thu c khi s dng thit b c phn gii cao. V tri hp thu cc i ca mt hp cht c thay i vi nm, ph thuc vo bn cht ca dung mi hay gi tr pH ca dung dch. Bc sng hp thu cc i c xc nh bng cch thng qua ph phn gii cao ca hp cht ng vi mt di hp thu trong mt vng bc sng no .

i lc, di hp thu ch thu c khi nghin cu trng thi m c nh th tinh kit ca cht hay dung dch. Tuy nhin cng c mt vi mu nghin cu th hi cng cho cu trc ph p, v ch c mt vi phn t cht cho ph thng.

3.2. S hp thu ca phn t

S tc ng photon ca bc x t ngoi v kh kin ln mt phn t c lp ch yu lm thay i trng thi in t, tc l Eel thay i nhiu nht, c ngha l s thay i ca mc nng dao ng v mc nng lng quay khng ng k so vi mc nng lng in t.

Eele >>Ed >>Eq nn: Etng EeleTa c th thy iu ny qua hnh sau:

th m t trng thi nng lng cc trng thi quay, dao ng v in t ca phn t.Trn th ta thy nng lng quay, nng lng dao ng nh hn rt nhiu so vi nng lng in t T l phn b gia cc mc nng lng l : 1000: 50: 1.

Sau khi hp thu nng lng c th c gii phng bng cch pht x bc x hay chuyn nng lng sang dng khc. Hu ht cc bc x chuyn bao gm l ln quang v hunh quang

th cho thy s chuyn t trng thi kch thch v trng thi c bn ca phn t, s gii phng nng lng c th xy ra bng cch di dng nhit hay di dng bc x hoc c hai. S chuyn i xy ra ngay tc th ( di phn triu giy), i vi nguyn t th tn s hp thu bc x bng tn s pht x khi chng chuyn t trng thi kch thch v c bn

3.3. S thay i cc orbital phn t trong qu trnh hp thu

Trong th cc hp cht hu c, khi quan tm nhng lin kt to ra, gia cc nguyn t nh C, H, O, N c s chuyn hin din cc in t lin kt , , v in t khng lin kt n ln cc orbitn phn lin kt *, * . S chuyn v ca cc in t cc orbital lin kt ln phn lin kt khi hp thu nng lng, hnh thnh ph gi l ph chuyn v.

Qu trnh chuyn v c xc nh bi bc sng ca n v h s hp thu mol ( mol-1.cm-1) ti bc sng ny.

3.3.1. Chuyn v *Kh nng chuyn v trong lin kt trong cc hp cht hu c tng ng vi mc nng lng cch bit gia hai orbital lin kt v phn lin kt *.. S chuyn v ny i hi mt nng lng kh ln, v vy qu trnh chuyn v nm trong vng t ngoi xa ( UV). y l l do v s tch cc hydrocacbon nh hexan v cyclohexan, trong phn t ch cha lin kt c xc nh r trong vng t ngoi hexan c max= 135nm ( = 10000).

Hexan v heptan c dng cho nh nhng dung mi trong vng t ngoi gn v chng hp thu mnh bc sng trn 200nm. Tt nhin hai dung mi ny khng ha tan hp cht hu c phn cc.

3.3.2. Chuyn v n *

S di chuyn ca cc in t khng lin kt n ln cc orbital * trong cc nguyn t nh O, N, S trong cc hp cht hu c vng ph t ngoi gn c cng khng ln. S dch chuyn ny dao ng 180nm cho alcol, dn xut halogen ca n l 190nm. i vi cc amin l 220nm

V d : Ete c max= 190nm ( =2000), metanol c max= 183nm ( =50)

Etylamin c max= 210 nm ( =800)

3.3.3 Chuyn v n *y l qu trnh dch chuyn c nng lng thp, mt in t t orbital khng lin kt n ln orbital phn lin kt *. y l qu trnh thng xy ra trong phn t c mt nguyn t cha bo ha in t. Hu ht cc qu trnh chuyn ny xy ra nhng phn t cha nhm chc cacbonyl (C=O) v bc sng hp thu t 270nm- 295nm. H s hp thu mol trong trng hp ny l thp. Bn cht ca cc dung mi c nh hng n bc sng hp thu v n tc ng n lin kt trong phn t.

3.3.4. Chuyn v *Cc hp cht ng phn vi etylen cha lin kt i trong phn t c kh nng hp thu mnh trong khong bc sng 170nm, v tr hp thu ph thuc vo s hin din ca nhm th v d etylen c max= 165nm ( =16000)

Nhng hp cht khng mu thng c ph hp thu trong vng cn t ngoi. Khi chng hp thu bc x th chng s chuyn ti trng thi thng qua c ch cho- nhn in t. Lc ny in t t orbital cho in t s chuyn ln orbital nhn in t to thnh nhng ion hay c s phn cc trong phn t Chuyn v dd*

Mt s mui v c , trong cu trc phn t c cha orbital d trng ( nh Cu,Ni, Mn) c kh nng chuyn v dd* ( Chuyn v c mc nng lng thp) trong vng kh kin, lm cho mui ca chng thng c mu. iu ny gii thch ti sao phc ca chng vi cc phi t nh CN-,NH3, H2O c mu nh Cu(NH3)42- c mu xanh.

3.4.S lin hp trong cho nhn in t

Mt hp cht l c s dch chuyn r rng khi m trng thi ring bit chng c th hp thu nhng phn nng lng c th thc hin s cho- nhn in t. Hin tng ny lin quan ti vic in t nhy t orbital lin kt cho ( to cation) ln orbital phn lin kt nhn ( to anion), tng ng vi s mt nng lng. V tr hp thu ca ph ty thuc vo kh nng ion ha ca cation v mc i in t ca nhm ht in t. Ga tr ( hp th mol trong trng hp ny thng ln)

Gin m t qu trnh dch chuyn in t. Trng thi kch thch c xem l s hnh thnh cc ion hay c s phn cc trong phn t3.5. Cc nhm chc

Nhm chc l nhng nhm nh c to thnh t nhng nguyn t, n lin quan ti qu trnh hp thu. Ti v tr cc nhm chc trong phn t cc dch chuyn in t xy ra, nn bc sng hp thu ca phn t hu c lin quan ti cc nhm chc trong phn t. Bng nhng my o bc sng hp thu cc i ngi ta tm c cc bc sng hp thu cc i cho tng nhm chc. Bc sng hp thu ca phn t chu nh hng ca tc ng ca cc nhm chc.

Sau y l bc sng hp thu cc i ca mt s nhm chc ca N

3.6. nh hng ca dung mi- Qu trnh solvate ha cc nhm chc

Bc sng hp thu v cng hp thu ca cc hp cht chu nh hng ca dung mi. S tc ng ca nhng dung mi khc nhau ln cc phn t lm thay i mc nng lng gia cc rng thi kch thch v c bn.Nghin cu vng hp thu v bc sng hp thu, chng ta c th bit c loi dch chuyn trong phn t khi chng hp thu.

3.6.1. Chuyn dch xanh

Trong mt vi dch chuyn, nhng dung mi phn cc th buc sng hp thu ngn hn so vi bnh thng. V d nh trong chuyn dch n * ca nhm cacbonyl trong mch phn t . Trong phn t hu c c s phn cc ca v tr C+-O- , nu dung mi l phn cc th v tr s c s tng tc ca in t n vi cc dung mi lm bn trng thi in t n( nng lng gim) . S gim nng lng trng thi n lm tng mc chnh lch nng lng gia n * , E tng dn ti bc sng hp thu gim nn ta gi l dch chuyn xanh.

Ch l nng lng trng thi * nhng trng thi n gim nhiu hn nn kt qu l mc chnh lch nhit gia hai trng thi tng

Ph hp thu ca benzophenol trong cyclohexan v etanol. Ta thy mc s chuyn dch xanh hay chuyn dch l ph thuc bn cht cu trc ca nhm vo bn cht ca dung mi.

3.6.2. Chuyn dch

Hin tng chuyn dch xy ra thng nhng hp cht hu c h etylen c lin kt ni i km bn.Trong dung dch th c s tng tc ca nhm phn cc ca dung mi vi in t , s tng tc ny trong dung mi phn cc mnh hn so vi dung mi khng phn cc. V vy mc chnh lch nng lng chuyn trong dung mi phn cc thp hn ( mc nng lng trng thi kch thch thp hn so vi trong dung mi phn cc ) , hp thu bc sng di hn.

3.7. nh hng ca s lin hp n hp thu

Ph hp thu ca nhng phn t l ng phn ca nhau, khc nhau bi mt nhm CH2 ca cc phn t hu c m trong cu trc phn t ca n c s lin hp, th bc sng hp thu ca cc phn t ny tng ln so vi di mch C. Nguyn nhn ca hin tng ny l do khi mch C cng di th hiu ng kin hp cng tng, dn ti mc chch lch gia hai trng thi kkch thch v c bn gim. Bc sng hp thu c xu hng v pha c bc sng di hn ( dch chuyn )

th m t nh hng ca hiu ng lin hp. Hiu ng ny l ngun gc to ra mu ca nhiu hp cht khc nhau trong thin nhin.

S hp thu ca cc hp cht thm, ph hp thu thu c phc tp hn nhiu so vi cc hp cht h etylen. S chuyn dch in t t * to nn s hin din cu trc ph.

Bng trn cho thy v tr hp thu cc i ca cc cht trong h polyetylen tng ln theo gi tr n( hiu g lin hp cng ln th bc sng hp thu cc i cng nh)

3.8. nh hng ca pH

pH ca dung dch m cht tan tn ti c nh hng ti ph. Phn ln cc hp cht, s tn ti hay bin i ca n c lin quan ti pH ca dung dch nh mt s ch th m chng ta thng gp.

Trn y l nh hng ca pH n dung dch phenolphtalein. Hp cht ny khng mu pH nh hn 8 v c mu hng sng pH ln hn 9.5

3.9. Quy tc Woodward- Fieser

T vic phn tch cu trc ca ph in t thng qua cu trc phn t, vo 1940 trc khi k thut xc nh nng lng lin kt ra i th Wood- Fieser v Scott xc nh c mi quan h r rng gia v tr hp thu cc i v cu trc phn t. Qu trnh kho st bao gm nhng hp cht c nhm dien, cabonyl , steroid. Kt qu th s kho st gia tnh ton kinh nghim v kt qu thc t c s sai bit rt t . Sau y l mt s v d:

Mt s quy tc:

*H thng dien: c tnh tyrn cn bng 1-3 butadien

Nhm mang mu (nm)

* 1-3 butadien217

* H thng ng vng+36

* 1 ni i ko di lin hp+30

* 1 ni i ca dien gn trc tip vo vng (C = )+5

* 1 nhm alkyl+5

* 1 nhm th RS+30

RO- , HO-+6

X-+5

R2N-+60

Th d :

+ 1-3 butadinen 217

+ h thng ng vng 36

+ 1 ni i ko di lin hp 5

+ 1 ni i gn vo vng 5

+ 4 nhm th alkyl 20

Tng cng = 308nm

Thc nghim = 309 nm

Ceton v aldehyde

C = C - C = C - C = O

Nhm mang mu (nm)

Ceton vng 6215

Ceton vng 5202

Aldehyde207

Ni i ko di lin hp+30

Dien ng vng+39

Ni i vng ngoi+5

Th alkyl ,,,+10,12,18,18

Th OH ,+35

Th OAC,,,+6

Th =O-Me ,,,+35,30,17,30

Th Cl ,+15,12

-Br ,+25,30

-n-R2+25

Th d :

Ceton vng 6 215nm

Din ng vng + 39

Ni i ko di lin hp + 30

Alkyl ,,, 10,12,18,18 + 58

3 ni i trctip vi vng + 15

Tng cng = 357nm

Thc nghim = 359 nm

Hp cht c dng:

Nhm X l : Alkyl = 246nm

OH,OR = 230nm

H = 250nm

Quy tc Scott

Nhm thV tr nhm

th ortoV tr nhm

th metaV tr nhm

th para

Alkyl3310

-OH,OR7725

-Br2215

-NH2151558

-NR2202085

V d: X l OH c = 230nm

Z l Br (para) +15nm

Theo l thuyt = 245nm

Theo thc nghim = 244nm

10. Thit b o quang ph t ngoi v kh kin

Thit b quang ph UV-Vis cha ba b phn chnh : Ngun to bc x- B phn phn tn bc x ( bao gm c b phn to bc x n sc)- Detector. Nhng thit b ny c th dng c lp khng ph thuc vo nhau, to nn mt thit b dng cho mc ch phn tch mu. Mu c th c t trong ng dn bc x trc hay sau b phn phn tn nh sng v ph nhn c c x l bng mt s thut ton khc nhau trn computer.

3.10. Ngun to bc x

Da vo bn cht ca qu trnh to ra bc x m ngi ta chia lm hai loi ngun bc x: Ngui bc x lin tc v ngun bc x khng lin tc

+ Ngun bc x lin tc.

Ngun bc x lin tc l ngun pht ra di cc bc x lin tc c di sng khc nhau, sau cc bc x ny i qua b phn to bc x n sc c bc x n sc trc khi i n mu

Ty vo di sng ca bc x cn pht ra , ngi ta dng cc loi ngun sau :

- Ngun t ngoi : gm c n hydro ( cha kh H2) v n deterium ( cha kh D2)

Cu to n :

Hot ng ca n : Th cao 2000 6000v p c vo hai in cc nhm , kch thch phn t bn trong, chuyn chng t trng thi nn( trng thi c bn) ln trng thi kch thch , khi cc phn t kh b kch thch khng bn pht ra nng lng di dng nhng bc x c bc sng xc nh tr v trng thi c bn, qu trnh xy ra lin tc nh vy v ta c nhng bc x cn thit. Vi loi n ny bc xa pht ra c = 180 375nm

- Ngun n thy c : pht ra nhng bc x thy c

Cu to n :

Hot ng : Ngi ta p t th khong 6 V vi cng dng ln , t nng dy tungsten. Dy ny chy v a kh tr trong n ln trng thi kch thch t pht ra bc x c =320 2500nm. Nhit n khong 30000K.

Ph pht x ca n Deuterium v cu to ca n Deuterium.3.10.1. Cc loi ngun o trong my quang ph

1. Ngun n- my o ti mt bc sng c nh

My o ti mt bc sng xc nh no nh trong my o quang. Di o rng nh b phn lc mu. Mu blank l mu ch c cha thuc th v dung mi m khng cha cu t cn phn tch, c o u tin tr i hiu ng hp th nn, sau mu chun v mu o c o theo th t t thp ln cao. B phn phn tch thu bc x n sc dng trong my ny c l cch t.

Cu to ca ngun o loi ny n gin, cc b phn in lin quan ti s pht x v n nh ngn cng khng i hi phc tp. V vy gi tr ca loi my ny tng i r.

2. Ngun n- My o nhiu bc sng nhau trong cng mt lc

y l thit b hin i, n cho php o cng mt lc cc bc sng khc nhau. Di ph thu c c trn 2000 vch ph bc x. Ph thu nhn c ch trong 1/1000 giy t vic nhn bit tc th ca detector. phn gii ph thuc vo kch thc ca diodes thng t 1-2 nm

3. My quang ph hai chm tia. Thit b o tt nht trong lnh vc ny vn l loi my quang ph hai chm tia. Trong mt ngun xuyn qua cuvet cha mu v mt ngun sng khc th i qua mu i chng ( mu chun hay mu blank ). Ngun sng khi i ti gng quay th chng s to ra hai ngun sng c bc sng nh nhau i qua hai cuvet. Trong thit b o hai ngun ny th ngi ta b tr hai detector thu nhn cng nh sng. Dng in lin quan ti hot ng ca ng quang nhn in( photomultiplier tube) nh hng ti nhy ca php o nh phn trm nh sng thu nhn bi detector.

u im ca loi my ny l :

Chng ta c th o mu v chun cng mt lc v c th kim sot c qu trnh o xem c g sai bit khng.

Loi tr c phn nh sng b sai lch khng i qua mu

Thit b ny c kh nng qut rt nhanh khong 30nm/ giy, nn chng c dng trang b trong cc my o hp thu.

3.11. B phn phn tn v to bc x n sc

Bc x pht ra t ngun c phn tch bi cch t b mt phng hay cong. B mt cch t c khong 1200 vch trn 1mm. Khi bc x n b mt ca cch t th c hin tng giao thoa, to ra nhng bc x n sc c bc sng xc nh. Sau bc x c chn ny uc tch bng cch i qua mt khe hp. Bc sng c to ra bng cch ngi ta thay i gc tip xc ca bc x khi n b mt cch t. ng dn c chiu di tiu c khong 0,2-0,5m cho phn gii tt nht.

Cu to ca mt s cch t :

a. Ebert thit k vi mt knh cu lm M3 khc phc phn bc x b phn tn.

b. Czeny-Turner thit k vi hai knh cu lm hp nht M3 v M4c. Thit k vi cch t lm Gc c th tch cch bit bc x mt bc sng xc nh 0,01nm. Chiu rng ca chm bc x n sc l ph thuc vo hp ca khe F

3.12. Detector

Detector l mt loi dng c quang hc dng thu nhn, pht tn hiu quang hc theo hiu ng quang in ca n . Trc y thu nhn cng ca chm sng ngi ta thng dng knh nh hay phim nh. Nhng dngc ny c in c nhy km, nht l knh nh. Knh nh c nhc im kh bo qun , b nh hng bi thi tit, m. Mt khc n l dng c trung gian nhn c trung gian nhn chm sng v sau s l tip mi c c vch ph.

Ngy ny dng c c dng nhiu nht l loi detector quang hc kiu ng c th khuych i c vi triu ln, ngi ta gi l nhn quang in ( photomultiplier) v mt loi detector c cu to l nhng diodes bn dn. Nhng diode bn dn ny s hp thu nng lng dng in sinh ra do dng bc x sau khi b hp thu mu.

Nhn quang in kiu ng ( photomultipliers tubes) l mt loi dng c thu nhn tn hiu quang hc c tnh cht vn nng , n nhy v chn lc cao. Vng ph hot ng ca cc detector dng ny thng t 190nm- 900nm. Tt nhin thng s ny ph thuc vo bn cht ca nguyn liu lm bn catot. H s khuych i ca detector loi ny khong 106 ln , i khi c loi ti 107. Nguyn liu ch to bn catot ca cc detector kiu ng l cc hp kim ca cc kim loi kim vi: Sb, Ga hay As.

V d nh : Cs-Sb, Ga-As, Na Cs, K -Sb

Nhng my quang ph thng thng, nhn quang in dng ng l c thit k nh ng hai cc, c nhy, rng khong o v tn hiu o rt chnh xc. Dng quang nng sinh ra khong 1ev, cho php xc nh bc sng ln hn 1100nm.

Trong h thng diode, cc diode c hnh dng ch nht bn trong kt ni vi bng kim loi. Dng in t c to ra t bc x sau khi i qua mu c tch trn bng kim loi, to ra nhng bc x t ta c ph thu c. n v o trong thit b nhn quang in l Watt.

3.3. C s ca phng php o quang

3.3.1.Tnh cht hp th nh sng ca h keo

Tnh hp th nh sng c nghin cu bi nh bc hc Lambert khi ng chiu mt lung nh sng n sc qua dung dich keo. ng nhn thy Lp dung dch keo b nng ln v cng tia l khi i ra khi lp dung dch keo nh hn so vi cng tia ti lp dung dch. iu ny chng t lp dung dch keo hp thu mt phn nh sng. Sau mt thi gian nghin cu ng rt ra c cng thc thc nghim sau:

Il=I0.e-kdTrong :IL : l cng tia l

I0 : l cng tia ti

k: h s hp th

d: dy cu lp dung dch keo

T y ta thy khi d tng theo cp s cng th Il gim theo cp s nhn

Sau ny Beer nhn thy h s hp th k t l vi nng ht nn c th biu din cng thc lin h gia k v nng ht C l :

k = .C

: l h s hp th mol

T y ta thy Il = I0. e- cd

t c gi l hp th

Ta c : A = .C.d c dng y = ax phng trnh m t s bin thin hp th nh sng theo nng ht

Trong k thut ngi ta o hp th nh sng ca cc dung dch bng nhng Cuvet c chiu dy c nh thng l 1cm.

i vi mt dung dch trong mt iu kin o nht nh th l hng s nn A t l vi C

3.3.2.C s phng php o quang

C s ca phng php o quang c da trn ng dng tnh cht hp th nh sng n sc ca cc h keo.

C th m t phng php ny nh sau: xc nh mt cht no c trong mu phn tch , ngi ta tin hnh cho cht cn xc nh to phc bn vi mt thuc th mt mi trng xc nh c pH xc nh .

Song song vi qu trnh trn ngi ta tin hnh trn mt lot bnh nh mc . mi bnh c cha dung dch cht cn xc nh c nng xc nh, v cng tin hnh to phc trong cng iu kin vi mu cn xc nh trn.Lc ny ta c dy mu chun c mu tng dn theo nng m chng ta pha. Ngi ta gi y l dy chun.

o mt quang ca dy chun nh vy ng vi nng :

C1 ta c A1C2 ta c A2

C3 ta c A3

C4 ta c A4

.

Cn ta c An

i vi mu cn xc nh :

CX ta c AXDng ng thng A theo C t xc nh gi tr Ax trn th t tm c gi tr Cx .

Trong thc t nh gi chnh xc ca qu trnh lm , thng ngi ta dng phng php bnh phng cc tiu x l s liu thu c. T phng php bnh phng cc tiu ngi ta tm c phng trnh y = ax trong y tng trng cho A v x tng trng cho C. Thay gi tr Ax vo phng trnh ta c gi tr Cx . V nh gi chnh xc ca qu trnh c th kim nh thng qua gi tr R2 . Gi tr ny phi t ti thiu l : R2 > 0,99 th ng chun mi t yu cu.

th c dng nh sau :

3.3.3.Nhng yu t nh hng n hp th nh sng.

T c s ca phng php ta thy vic o hp th nh sng ca dung dch cng chnh xc , gi tr thu gia cc dung dch chun l hp l th kt qu phn tch ca chng ta cng d chp nhn.Nn trong k thut phn tch ngi ta c gng loi b nhng sai st trong qu trnh tin hnh c nh vy th kt qu mi chnh xc . Sau y l mt s yu t nh hng n qu trnh o.

a. Vn hnh my

+ Cn to bc x tht n sc c s hp th c thnh chn lc v K l hng s .

+ Chn bc x ng vi hp th cc i theo gin A = f ()

+ Gi nhit c nh 30C

+ Chn loi cuvet thch hp tt nht l thch anh

+ C th chn cuvet dy hn c D ln hn

+ Phi lm mu trng loi nh hng ca dung mi v cu t ph. Chnh my c A = 0 v T = 100%

b. K thut o

+ C th tng chnh xc ca php o bng cch tng thc o khi mu c nng qu cao hay qu thp ( phng php o vi sai )

+ Nu mu c nng qu cao th , dng dung dch chun c nng thp hn iu chnh my c T = 100%

+ Nu mu c nng qu thp , dng dung dch chun c nng cao hn iu chnh my c T = 0%

+ Hy dng hai dung dch chun c nng cn nng dung dch mu, iu chnh my T = 100% v T = 0%

c. Bn cht dung dch

+ Chn nng dy chun sao cho c t l tuyn tnh D = f(C )

+ C th khi pha long dung dch s nh hng ti s tn ti ca phc lm cho mu ca dung dch gim dn ti mt quang o c l gim

V d : [Cu(NH3)4]2+ + 2H2O [Cu(NH3)3H2O]2+ + NH4OH

+2 H2O

[Cu(NH3)2H2O]2+ + NH4OH

+ Yu t pH rt quan trng khi gi tr pH ca dung dch thay i th n s nh hng ti s tn ti ca phc,tc l nh hng ti gi tr o A

V d : 2 CrO42- +2 H+ Cr2O72- + H2O

d. Anh hng ca thi gian:

Mi phc hnh thnh u c bn ca n v sau mt thi gian di tc dng ca mi trng n b phn hu v vy cn phi o trong khong thi gian bn ca phc. Lc th cng mu l ln nht , hp th l cc i.

UV-3101UV-1650PC

UV-3600

3.3.4. Mt s v d p dng phng php o quang

a. Xc nh hm lng Fe c trong nc

+ Nguyn tc:

St trong dung dch c kh thnh dng Fe2+ (tan trong nc) bng cch un si trong mi trng acid v hydroxylamine, sau Fe2+ to phc c mu vi 1,10 phenanthroline pH = 2,8 ( 3,5. Mi nguyn t Fe2+ s kt hp vi ba phn t ca phenanthroline to thnh phc cht mu cam. Cng mu tun theo nh lut Lambert-Beer v ph thuc vo pH. Phn ng s t tc cc i khi pH ca mi trng trong khong t 2,9 ( 3,5 v s dng mt lng tha phenanthroline. Cc phng trnh phn ng c biu din nh sau :

Fe(OH)3+3H+(Fe 3++3H2O

4 Fe 3++ 2NH2OH ( 4 Fe 2++ N2O + 4H+ + H2O

(mau o cam)

1.3. Tr ngi:

Nhng cht oxy ha mnh nh cyanide, nitrite v phosphate (polyphosphate mnh hn orthophosphate), chromium, zine vi hm lng ln hn st 10 ln, cobalt, copper ln hn 5mg/l v nicken ln hn 2 mg/l u gy nh hng n kt qu phn tch. Bismuth, cadmium, mercury, molybdate v silver kt ta vi phenanthroline. Trong qu trnh thc hin th nghim, bc un si vi acid nhm chuyn polyphosphate thnh orthophosphate, loi b nh hng ca nitrite v cyanide. Thm mt lng tha phenanthroline loi b nhng sai s gy ra bi cc cht oxyha mnh v to phc vi mt s ion kim loi c trong dung dch. Nu hm lng cc ion kim loi qu cao, cn phi s dng phng php trch ly.

Nu mu c mu hay cht hu c, x l mu bng cch un si mu nhiu gi vi acid HCl 1:1 trong cc c quai bng silica, s hay platinum. Khi mu cn, t nh, phn tro cn li c ha tan bng acid. Nu hm lng cht hu c qu cao, bc phn hy s c thc hin trc giai on trch ly.

Phng php phenanthroline c th xc nh hm lng st nh nht l 10(g.

Dung dch chun m:

20ml H2SO4 m c vo 50ml nc ct v thm vo 1,404 Fe(NH4)2(SO4)2.6H2O. Sau khi dung dch ng nht (1,00ml = 200(g Fe = 200ppm).

Dung dch chun : chun b mi khi s dng.

Ly 50ml dung dch lu tr st cho vo bnh nh mc 1000ml, thm nc ct ti vch nh mc (1,00ml = 10,00(g Fe= 10ppm).

Thc hnh:

Xc nh St tng cng : (Fe tc)

Mu phi c lc u trc khi phn tch, ly 50ml mu cho vo erlen. Nu th tch mu c hm lng st cao hn 200(g, s dng mt lng mu t hn v pha thnh 50ml. Thm 2ml HCl m c v 1ml NH2OH.HCl. Thm vi vin bi thy tinh vo erlen, un si n khi th tch cn khong 15 ( 20ml (nu mu b cn, cho vo 2ml HCl m c v 5ml nc ct).

Lm ngui mu nhit phng, chuyn dung dch vo bnh nh mc 100ml, thm 10ml dung dch m NH3C2H3O2 v 4ml dung dch phenanthroline. Cho nc ct ti vch nh mc v lc u, sau khong 10 (15 pht cho cng mu t cc i v n nh. o hp thu trn my spectrophotometer bc sng 510nm.

Thit lp ng chun v xc nh mu

S dng dung dch chun c nng 10ppm .

Pha lot dung dch chun st nh sau :

STT01234M1M2

V chun (ml) Fe 10ppm0123400

V mu nc (ml)33

V HCl m c (ml)0,50,50,50,50,50,50,5

V NH2OH.HCl (ml)1111111

V NaOH 30% (ml)0,50,50,50,50,50.50.5

V m Amoniaxetat(ml)3333333

V 1-10 phenanthroline (ml)1111111

H2O ct (ml)4321011

Hm lng ppm Fe01234Cx1Cx2

Ch thch :

* un si cho ti th tch dung dch cn khong 10(15 ml.

* nh mc thnh 100ml bng nc ct. Lc u v o hp th.

Ly mt mu nc ct v thc hin tt c cc bc nh trn lm mu trng chun.

Nu mu b c v c mu, thay v s dng nc ct lm mu chun trng, s dng chnh mu lm mu chun trng v x l mu qua tt c cc bc nh trong qu trnh thc hin nhng khng cho phenanthroline.

TNH TON

Sau khi c hp th ca mt lot chun. V gin A = f(C), s dng phng php bnh phng cc tiu lp phng trnh y= ax + b. T tr s hp th ca dung dch mu Am suy ra Cm t phng trnh trn. Kt qu biu din bng n v mg/l.

a. Xc nh NO3- trong nc

Nguyn tc :

Phn ng gia nitrate v brucine cho sn phm c mu vng c p dng xc nh hm lng nitrate bng phng php so mu. Cng mu c o bc sng ( = 410nm. Tc phn ng gia nitrate v brucine chu nh hng r rt vo lng nhit ta ra trong qu trnh phn ng. V th, cc cht phn ng c thm vo ln lt v mt khong thi gian chnh xc ti nhit bit. Nng acid v thi gian phn ng c la chn to mu tt nht v n nh. Phng php ny thch hp vi c nc ngt v nc bin, vi hm lng N-NO3 xp x 0,1-2 mg/l.

Cc nh hng :

S hin din ca tc nhn oxy ha c th c loi tr bng cch thm cht phn ng orthotolidine. Tr ngi bi clor d c th b loi bng mt lng sodium arsenite khi chlor d khng qu 5 mg/l. Mt lng d sodium arsenite nh khng nh hng n vic xc nh nitrate. Ion Fe2+, Fe3+ v Mn4+ s gy nh hng nh, nhng nu hm lng cc ion ny nh hn 1mg/l th nh hng khng ng k. Tr ngi do nitrite gy ra khi N-NO2 < 0,5 mg/l c ngn nga bng acid sulfanilic. Hm lng cht hu c cao trong nc thi cng s gy tr ngi cho vic xc nh nitrate.

Dung dch NO3- lu tr 100ppm : Ha tan 0,7218g Anhydrous Potassium Nitrate KNO3 + nc ct = 1 lt.

Dung dch NO3- chun 50 ppm . Pha long 50ml dung dch lu tr thnh 100ml

Qu trnh xc nh

Nu mu c chlorine, kh lng clor d ny bng cch thm 1 git sodium arsenite cho mi 0,1mg Cl2 trn 50ml mu.

Chun b dung dch tham chiu nh sau:

STT01234M1M2

Chun NO3 - 50ppm01234

Mu nc xc nh22

H2SO m c3333333

Brucine1111111

H2O6543244

Cppm05101520Cx1Cx2

Th t thc hin nh sau :

Do phn ng xy ra ph thuc vo rt nhiu nhit to ra t qa trnh hydrat ha ca H2SO4 m c, nn khi cho H2SO4 vo th lp tc cho thuc th Bruccine vo lc u. yn trong bng ti 20 pht, em ra nh mc thnh 10ml nh trong bng , sau em i o hp th

o hp thu A ( = 410nm.

4. Cch tnh

T lot chun o hp thu.

V gin A = f(C), s dng phng php bnh phng cc tiu lp phng trnh

y = ax .

T tr s hp thu Am ca mu tnh nng Cx.

CHNG 4:PHNG PHP PH AAS V NG DNG TRONG PHN TCH THC PHM

4.1 C s ca phng php ph hp thnguyn t AAS

4.1.1 S xut hin ca ph hp th nguyn t

Nguyn t bao gm ht nhn v cc in t chuyn ng xung quanh ht nhn theo nhng obital c nng lng xc nh. Cc in t trong nguyn t c phn b vo cc orbital theo quy lut t thp ti cao, v iu kin thng nguyn t trng thi bn vng, c nng lng thp nht. Nu cung cp nng lng cho nguyn t (in nng , nhit nng, ha nng) th trng thi khng tn ti na th in t s chuyn ln mc nng lng cao hn khi nguyn t b kch thch, nhng trng thi ny khng bn vng. Nguyn t ch lu li trng thi ny nhiu nht l 10-8 giy. Sau n lun c xu hng tr v trng thi c bn gii phng nng lng, nguyn t gii phng ra nng lng di dng cc bc x. Nu nguyn t b kch thch bi ngun bc x in t th chng ta c ph hp thu nguyn t.

Nu nng lng gii phng di dng bc x in t th ta ph ph pht x v nu tn pht pht x bng tn s hp thu th ta c s pht x ton phn. trng thi hi, nu nguyn t b kch thch bi mt chm tia sng c nhng bc sng (tn s) mang nhng nng lng xc nh ng ng vi nng lng cn thit chuyn cc in t t trng thi c bn ln cc trng thi kch thch tip theo.

Cc nguyn t t do s hp th cc bc x c nng lng xc nh . Ph sinh ra trong qa trnh ny gi l ph hp thu nguyn t. Nu gi nng lng ca tia sng b nguyn t hp th l E

Ta c:

E = ( Em E0 ) = h hoc E = h.c /

Eo : nng lng trng thi c bn

Em: nng lng trng thi kch thch

h : hng s Planck, C : tc nh sng

: di sng ca vch ph hp th

nhy ca cac phng phap:

ng vi mi mc nng lng in t c nhiu mc nng lng dao ng. ng vi mi mc nng lng dao ng c nhiu mc nng lng quay. S hp th nng lng ca phn t c tnh c trng. Mun chuyn t mc nng lng E0 ln mc nng lng E1 cn mt bc x c nng lng:

E = hv = E1- E0

Ch nhng bc x c nng lng ng vi khong cch ca cc mc nng lng trong phn t mi c hp th. Qu trnh nguyn t ha c th thc hin vi phng php ngn la: bng cch phun dung dch phn tch trng thi aerosol vo ngn n kh; hoc khng ngn la: nh tc dng nhit ca l garphit. Cht nghin cu b nhit phn v to thnh cc nguyn t t do. Trong iu kin nhit 1500 3000oC a s cc nguyn t c to thnh trng thi t do. By gi nu ta hng vo lun hi nguyn t mt chum bc x in t c tn s bng tn s cng hng, cc nguyn t t do s hp th cc bc x ny lm gim cng chm bc x in t

4.2 Nguyn tc ca phng php

4.2.1 Nguyn tc ca phng php

nh ngha: Phng php phn tch da trn c s o ph hp thu nguyn t ca mt nguyn t c gi l php o ph hp thu nguyn t

Mun thc hin c php o ph hp thu nguyn t ca mt nguyn t cn phi thc hin qu trnh sau:

1/ Mu t dng lng di tc dng ca u t c nhit ln ti 30000C chuyn thnh trng thi hi ca cc nguyn t t do( m my nguyn t)- y l qa trnh ha hi v nguyn t ha mu.

2/ Mt chm tia sng bc x c trng ca nguyn t cn phn tch c chiu qua m hi nguyn t. Cc nguyn t ca nguyn t cn xc nh s hp th nhng bc x nht nh v to ra ph hp th ca n.

3/ Nh vo h thng quang ph ngi ta thu ton b chm sng sau khi i qua m my nguyn t v chn mt vch ph hp th ca nguyn t cn xc nh o cng ca n. Cng ca vch ph hp th t l thun vi nng ca nguyn t cn xc nh. Cc nguyn t cng nh phn t hp th bc x in t theo nh lut Lambert- Beer

nh lut Lambert- Beer:

Khi chiu mt chm bc x n sc i qua mt dung dch, hp th bc x n sc ca dung dch t l vi nng v chiu dy ca lp dung dch .

To c cng thc:

Vi:

A: hp thu

K : H s hp x ty thuc vo lc dao ng ca php chuyn di in t gy ra s hp x.

L: Chiu di ngn la trong phng php F-AAS hoc chiu di on ng i qua l GF-AAS.

C: Nng hi nguyn t cn xc nh trong Plasma.

I0,: Cng pht x pht ra t n cathode rng ti bc sng .

I: Cng hp x sau khi ra khi mi trng hp x. Thc t cng bc x sau khi i qua ngn la cha mu.

iu kin thu c ph hp th nguyn t

+ Cc nguyn t trng thi ri rc khng lin kt ha hc vi nhau

+ C mt ngun sng ngoi thch hp (thng chn n cathode rng ca chnh nguyn t cn thu ph hp x) di vo m hi nguyn t.

+ C mt thit b phn tch ph v ghi o thch hp.

4.3 Thit b php o ph AAS.

Thit b php o ph AAS ch yu bao gm nhng chi tit quang trng sau:

(1) Ngun pht tia bc x : thng l n cathod rng (hollow cathode lamp) : dng pht ra cc bc x n sc, c trng cho tng nguyn t.

(2) H thng nguyn t ha : dng chuyn mu (thng l ion, th lng) t dng phn tch dng lng sang th hi nguyn t:

C hai loi k thut nguyn t ha mu :

- Nguyn t ha bng ngn la ( Kh + Axetylen)

- K thut nguyn t ha khng ngn la

K thut nguyn t ha khng ngn la thng s dng :

-L grapht

- B to hydrua (hydride vapor generator HVG).

- B ha hi lnh phn tch thy ngn (MVU)

(3) H thng my quang ph : b n sc

(4) B n sc : thu phn ly v chn tia sng (vch ph) cn o nhm loi bt cc tia gy nhiu, n sc thm mt ln na nh sng trc khi vo u d.

(5) u d (photomultiplier tube) : chuyn tn hiu quang thnh tn hiu in

(6) B phn tip thu v x l tn hiu.

4.3.1 B phn pht tia bc x

Nh ni trn, trong phng php hp thu nguyn t(AAS) ngun pht ra bc x phi pht ra nhng bc x ph hp vi bc nhy ca nguyn t cn phn tch. t c iu ngi ta dng ngun kch thch thch phi lun hin din m hi nguyn t ca nguyn t cn phn tch khi lm vic.

n phi pht ra ngun bc x mnh v n nh, cc vch ny phi rt hp. V vy thng ch to mi nguyn t ha hc mt n ring nh th lm tng tnh chn lc trong phng php AAS.

C 2 loi n c s dng l n cathode rng (hollow cathode lamp: HCL) v n phng in khng cc Electrodeless discharge lamp: EDL).

n cathode rng(HCL HOLLOW CATHODE LAMP)

Cu to gm 4 phn

Phn 1: Thn n

Thn n, v n, ca s lm bng thy tinh hoc thch anh. Nguyn liu lm ca s n phi trong sut trong vng UV hoc VIS ty thuc vo loi n ca tng nguyn t. B cc in cc catot v anot lm bng nha PVC.

Phn 2: in cc

Catot : C dng hnh xylanh hoc hnh ng rng, c ch to bng chnh kim loi cn phn tch c tinh khit cao (>99.9%). Dy dn ca catot l W hoc Pt . Bao quanh catot c lp mica khng dn in m bo s phng in tp trung vo catot v tng cng vch cng hng.

i vi kim loi c im chy thp c ph mt lp mng trn ct ng. i vi kim loi cng hoc gin th p bt hoc ch thnh hp kim lm catot.

Anot: c ch to bng kim loi tr v bn nhit nh W hoc Pt. c t bn cnh catot hoc l 1 vng bao quanh catot.

Phn 3: Kh trong n

Kh np vo n khng c pht ra ph lm nh hng n chm tia pht x ca n.Trong iu kin nht nh, t s gia cc nguyn t b ion ha v cc nguyn t trung ha phi khng i n lm vic n nh. i vi kim loi c nng lng ion ha cao cn s dng kh Ne v Ne c nng lng ion ha cao hn Ar. Trong n phi ht ht khng kh v np vo kh tr: Heli, Ar, Ne ( tinh khit >99.9%) vi p sut 515 mmHg. Thay Ne bng Ar trong trng hp vch cng hng ca nguyn t cn xc nh k cn vch ca Ne. Kh Heli t c s dng do s tc ng vo catot km v s hao ht kh Heli trong n xy ra nhanh do Heli hp ph ln trn b mt n lm gim p sut kh trong n v gim tui th ca n.

Phn 4: Ngun nui n

Th lm vic thng t 220 250 (V).

Ngun in mt chiu n nh.

Cng dng lm vic t 3 50 (mA).

Khi s dng khng nn dng n dng in cc i v n mau hng, nhy v lp li ca php o km. Cng dng s dng tt nht l t 60-85% dng gii hn cc i ghi trn n HCL. Mun c nhy cao, nn s dng cng dng gn gii hn di. Mun c n nh cao, nn s dng cng dng gn gii hn trn.

Nguyn tc hot ng ca n HCL bao gm 3 bc:

B1: Khi n lm vic, gia hai cc xy ra s phng in kh, lm ion ha kh tr thnh ion. Kh tr s dng c th l Ar hoc Ne .

B2: Ion kh tr c tng tc bi in trng p vo catot lm sinh ra nguyn t kim loi trng thi hi t do. .

B3 :Nguyn t kim loi t do b va p tip tc v chuyn thnh trng thi kch thch ri pht ra bc x c trng. Chm tia pht x ny l ngun tia n sc chiu qua mi trng hp thu thc hin php o AAS.

n phng in khng in cc (EDL Electrodeless Discharge Lamp)

Cu to bao gm 4 phn

Phn 1: Thn n

L ng thch anh chu nhit, mt u n EDL cng c ca s S, trong sut vi chm sng cn phn tch. Cun cm bng ng cng sut 400-800 W c ni vi ngun nng lng cao tn HF nui n lm vic. Ngoi cng l v n chu nhit.

Phn 2: Cht trong n

Kim loi hoc mui (iodua) ca kim loi ca nguyn t d bay hi thay cho catot trong n HCL. y chnh l ngun cung cp tia pht x ca nguyn t phn tch khi chng b kch thch. p sut hi kim loi trong n khong 1 1.5 mmHg v nhit t 500 800oC.

Phn 3: Kh trong n

n phi c ht ht khng kh v np vo n kh tr Ne, Ar, Heli p sut thp (khong vi mmHg).

Phn 4: Ngun nui n:

Dng ngun nng lng cao tn cm ng in t nui n EDL lm vic, c ch to theo 2 tn s:

Tn s sng ngn 450MHz n EDL sng ngn.

Tn s sng radio 27.12MHz n EDL sng radio.

Tm li: V cu to, n EDL thc cht l ng phng in trong mi trng kh tr c cha nguyn t cn phn tch vi nng nht nh ph hp to ra chm tia pht x ch bao gm mt s vch ph nhy c trng ca nguyn t phn tch.

Nguyn tc hot ng ca n EDL nh sau: di tc dng nng lng t ngun cao tn lm ha hi cc mui kim loi ang t do, sau nguyn t kim loi ang t do chuyn ln trng thi kch thch v pht ra bc x c trng khi n lm vic.

n EDL cung cp bc x c cng mnh hn nhiu so vi HCL

Php o n EDL c nhy v chnh xc cao hn HCL (xt cng 1 nguyn t).

4.3.2 B phn nguyn t ha

y l qu trnh chuyn cc cht cn phn tch thnh cc nguyn t t do dng hi, cho php nguyn t hp thu nh sng nhng bc sng rt c trng

C hai kiu nguyn t ha:

(1) S dng ngn la (Flame)

(2) Khng s dng ngn la (Flameless)

- S dng l graphite (Graphit Furnace Atomisation-GFA)

- S dng b to hydrua (hydride vapor generator HVG)

- B ha hi lnh phn tch thy ngn (MVU)

4.3.2.1 K thut nguyn t ha bng ngn la

Ngn la c to thnh bng cch t chy hn hp ca cht oxi ha (thng l khng kh hoc N2O) v nhin liu (thng l acetylene).

Nhit ca ngn la gip cho qu trnh nguyn t ha xy ra. Tin trnh xy ra i qua nhiu giai on c th tm tc hnh sau:

Cc bc hnh thnh hi ngyn t:

+ Bay hi dung mi, ch cn li cc cht rn

+ Cc cht rn s bay hi di tc dng ca nhit

+ Di nhit cao cc phn t s b phn ly thnh cc nguyn t t do

+ Mt phn nguyn t s b ion ha thnh cc ion

S lng ion hay phn t s ph thuc vo bn cht ca tng nguyn t cng nh nhit ngn la

Qu trnh by hi dung mi

+ Mu sau khi vo b phun mu s c phn tn thnh cc ht rt nh di dng sng m, khi i qua mt mt vin bi lm bng ceramic

+ Mu di dng sng c i vo ngn la.

+ Cc dung mi bay hi ti y

+ Qu trnh bay hi dung mi s to thnh sol kh bao gm cc ht cht rn dng nng chy

thch hp

Qu trnh bay hi cht rn

+ Sau khi bay hi dung mi, cht rn do c nhit bay hi cao hn s vn cn tn ti trong ngn la di dng b nng chy.

+ Di tc dng tip tc ca ngn la nhit cao, n s b bay hi v phn ly thnh cc nguyn t t do.

+ Ty thuc vo bn cht ca cht m c th l qu trnh to phn ly xy ra trc hay sau qu trnh bay hi

Cc yu t nh hng ti qu trnh bay hi v phn ly:

+ Nng lng ca ngn la phi ln lm bay hi hon ton v b gy lin kt

+ Nhit cng cao cng c khuynh hng tng kh nng bay hi ng thi gim s to thnh ca cc oxit vn chu nhit cao. Qu trnh bay hi khng hon ton s dn n hin tng khng tuyn tnh ca ng chun

+ Kch c ht sol kh: Qu trnh bay hi cng mnh khi c ht i vo bung nguyn t ha cng nh.

Cu trc ngn la:

V hnh dng cu to v s phn b nhit ca ngn la, n kh gm ba phn nh sau:

Phn mt (a). Phn trong cng st ming n l phn ti (a). Trong phn ny

cht t c trn v nung nng chun b t chy phn hai (b). Nhit trong

phn ny thp (700-12000C).

Phn hai (b) l li ca ngn la.

Trong phn ny xy ra cc phn ng t chy cht kh. N khng mu hay c mu xanh nht v nhit l cao nht. Chnh nh b l ch c nhit cao nht ca ngn l a. Nu t bng hn hp kh axtylen v oxy hay khng kh nn th nhit ca ngn la c cung cp nh phn ng:

2C2H2 + 2O2 = 4CO + 2H2 + Q

Phn th ba (c) l v ca ngn la.

Trong phn ny thng xy ra cc phn ng th cp, c mu vng v nhit thp. N to thnh ui v v ca ngn la. Do s phn b nhit ca ngn la nh vy, nn kh phn tch phi a mu vo vng c nhit cao nht. l vng b ca ngn la v trong vng ny cc qu trnh s n nh, v hiu sut kch thch ph s cao nht.

Tc chy ca ca ngn la ph thuc vo:

+ Loi kh oxi ha v kh t.

+ T l thnh phn ca loi kh oxi ha v kh t v tc phun ca chng. Cc thnh phn ny rt quan trng trong vic xc nh n nh cng nh hnh dng ca ngn la

Nhit ngn la theo loi kh

4.3.2.2 K thut nguyn t ha bng l Graphit

c im v nguyn tc chung k thut nguyn t ha khng ngn la

c im: K thut nguyn t ha khng ngn la ra i sau k thut nguyn t ha trong ngn la. Nhng k thut ny c pht trin rt nhanh v hin nay ang c ng dng rt ph bin, v k thut ny cung cp cho php o AAS c nhy rt cao (mc nanogam ppb); c khi gp hng trm n hng nghn ln php o trong ngn la. y l u im chnh ca k thut nguyn t ha khng ngn la. Do , khi phn tch lng vt cc kim loi trong nhiu trng hp khng cn thit phi lm giu s b cc nguyn t cn xc nh. c bit l khi xc nh cc nguyn t vi lng trong cc loi mu ca y hc, sinh hc, dc phm, thc phm, nc gii kht, mu, srum.

Tuy c nhy cao nhng trong mt s trng hp, n nh ca php o khng ngn la thng km php o trong ngn la, nh hng ca ph nn thng rt ln. l c im v cng l nhc im ca php o ny. Song vi s pht trin ca vt l v ca k thut o hin i, ngy nay ngi ta c th khc phc c nhc im ny khng kh khn lm. V th cc h thng my o ph hp th theo k thut khng ngn la ca nhng nm 1980 lun lun c km theo h thng b chnh nn v n nh ca n cng khng km cc h thng ca php o trong ngn la v m bo nhy cao c ppb i vi nhiu nguyn t.

Mt c im na ca php o khng ngn la l i hi mt lng mu tng i nh. Thng thng mi ln o ch cn lng mu t 20 n 50L. Do khng cn nhiu lng mu phn tch, vic chun b mu cng d dng v khng tn nhiu ha cht cng nh cc dung mi tinh khit cao t tin.

V nguyn tc: k thut nguyn t ha khng ngn la l qu trnh nguyn t ha tc khc trong thi gian rt ngn nh nng lng ca dng in cng sut ln v trong mi trng kh tr. Qu trnh nguyn t ha xy ra theo bn giai on k tip nhau: sy kh, tro ha mu, nguyn t ha v lm sch l Graphite. Trong hai giai on u l chun b cho giai on nguyn t ha t kt qu tt. Nhit trong l graphit l yu t quyt nh mi s din bin ca qu trnh nguyn t ha mu.

Qu trnh lm kh mu

Tng t qu trnh loi dung mi trong phng php F- AAS, dung mi s c bay hi. Thng thng nhit qu trnh ny khong 110oC (trnh si qu mnh lm bn mu).

Vic la chn nhit thng ph thuc vo nhit bay hi ca dung mi cng nh trnh xy ra hin tng bn mu lm phn tn hoc mt mu. thc hin qu trnh sy tt, i vi mi mt loi mu cn phi tin hnh nghin cu chn nhit v thi gian sy cho ph hp. Nhit v thi gian sy kh ca mi loi mu ph thuc vo bn cht ca cc cht trong mu v dung mi ho tan n.

Qu trnh tro ha

Trong qu trnh ny cc hp cht hu c trong mu b tro ha hoc chuyn thnh nc, CO2 v cc hp cht v c. Tip hp cht ny c nung nng, nng chy hay b phn hy ty theo nhit tro ha chn v ty thuc vo bn cht ca hp cht mu tn ti trong l Graphite sau khi sy kh. Lc ny mu c luyn thnh th nng chy ng nht. ng thi y cng c s phn hu ca mt s mui khng bn thnh oxit hay mui hay oxit. iu kin l tng l nhit cao loi b cc hp cht bay hi m khng lm mt cht phn tch. Giai on ny c nh hng rt nhiu n kt qu phn tch, v mt s hp cht c th b phn hu mt trong giai on ny, nu nhit tro ha l qu cao. L thuyt v cc kt qu thc nghim xc nhn rng, tro ha mu t t v nhit thp hn nhit gii hn th php o lun lun cho kt qu n nh. Mi nguyn t c mt nhit tro ha gii hn gi l Tr trong php o ETA-AAS. Nhit tro ha gii hn l nhit m s tro ha mu nhit v nh hn n, th cng vch ph hp th l khng i. Cn nu tro ha mu nhit ln hn nhit th cng vch ph b gim v khng n nh. Nhit tro ha gii hn ca mi nguyn t rt khc nhau, n ph thuc vo bn cht ca mi nguyn t v ph thuc vo dng hp cht m nguyn t tn ti, cng nh matrix (cht nn) ca mu.Ni chung, v mt ha hc, cc nguyn t bn nhit v tn ti trong cc dng hp cht

bn nhit thng phi tro ha luyn mu nhit tng i cao. Nh Si c nhit tro ha gii hn l 1100oC, Ni l 1000oC, cn Pb l 600oC

Nn khc nhau ca mu (matrix effect), nht l cc cht nn bn nhit. Mt v d v vn ny khi o ph hp th nguyn t ca Mg trong cc nn khc nhau nh hnh di y

Nhit ti hn ca mt s nguyn t ph bin

Qu trnh nguyn t ha

y l giai on cui cng ca qu trnh nguyn t ha mu, v l giai on quyt nh cng ca vch ph. Hiu qu qu trnh ny chu nh hng bi hai giai on trn. Giai on ny c thc hin trong thi gian rt ngn, thng thng t 3 n 6 giy. V vy tc tng nhit li l rt ln gn nh ngay tc khc n nhit nguyn t ha. Tc tng nhit thng l t 1800 - 2500oC/giy, bng tc tng nhit ti a ca my. Mc nguyn t ha ca mt nguyn t rt khc nhau. ng thi mi nguyn t cng c mt nhit nguyn t ha gii hn gi l Ta. Nhit Ta ny ph thuc vo bn cht ca mi nguyn t, trng thi v thnh phn ca mu m n tn ti, nht l cht nn ca mu.

Cc kiu hnh thnh nguyn t ha trong l GraphitS ha hi ca cc hp phn mu dng phn t.

Nu nhit ha hi ca cc hp phn mu nh hn nhit phn li ca chng th cc hp phn mu ny s ha hi dng phn t, sau chng b phn li thnh cc nguyn t t do. (Eh < Ea). Tiu biu cho cc hp cht thuc loi ny l cc oxit Sb2O3, Ga2O3, cc mui halogen ca cc kim loai nh SbCl5, SnCl4, SnBr4, AlCl3, TiCl 4, GaCl3, cc mui axetat, Clorat ca kim loi, v.v... C ch din bin ca cc hp cht loi nyc th minh ho theo hai kiu s sau y - C ch chnh 1:

(a) MxXy(r,l) MxXy(k) xM(k) + X

(b) MxOy (r,l) MxOy(k) xM(k) + O2 (c) M(k) + n(hv) ph AAS

Qu trnh (a) xy ra i vi cc mui halogen kim loi v qu trnh (b) l i vi cc oxit kim loi d ha hi. Nh cc hp cht ZnCl2, CuCl2, FeCl3, CdCl2,Cn qu trnh (c) l s hp th bc x ca nguyn t, to ra ph.

Sau y l vi v d v c ch ny:

CdCl2(r,l) CdCl2(k) Cd(k)

CuCl2(r,l) CuCl2(k) Cu(k)

S phn li ca cc phn t cht mu trc khi ha hi.

Khuynh hng ny thng xy ra i vi cc phn t c nhit phn li nh hn nhit ha hi phn t ca chnh n Eh > Ea. Cc phn t thuc loi ny, di tc dng ca nhit trong cuvet graphit, trc ht chng b phn li thnh cc monooxit hoc thnh cc nguyn t t do trng thi rn, hay lng, ri sau mi c chuyn thnh th hi theo cc tnh cht ring ca sn phm va c hnh thnh. Din bin ca qu trnh thuc loi ny c th minh ho theo cc s di y:

C ch chnh 2: (f) MxXy (r,l) xM(r,l) + yX(k) xM(k)

xM(k)

(g) MxXy(r,l) xMO(r,l) + yX(k)xM(k)

xM(k)

(h) MxOy(r,l) xM(r,l) xM(K)

(i) MxOy(r,l) xMO(r,l) xM(r,l) xM(k)

Sau l qu trnh hp th bc x ca cc nguyn t M(k).

M(k) + n(vh) Ph AAS

Cc qu trnh (f) v (g) ny l i vi cc mui ca kim loi vi nitrat, cacbonat, sufat, photphat, ngha l cc mui c oxy. Cc qu trnh (h) v (i) l i vi cc hp cht oxit. Cc qu trnh theo cc c ch ny thng km n nh v cho kt qu c nhy thp hn cc qu trnh ca cc mui halogen trn. Tiu biu cho s din bin theo kiu ny l cc mui cacbonat, sunphat v photphat ca kim th Ca, Ba, Si.

V d: FeCl3(r,l) Fe(r,l) Fe(k)

Mn(NO3)2(r) MnO (r,l) Mn(k)

CaO(r) Ca(r) Ca(k)

V2O5(r) VO(r) V(k)

Nh vy, cc qu trnh ny xy ra trong cuvet nh th no ty thuc vo:

+ iu kin nguyn t ha mu (ch yu l nhit ).

+ Tnh cht nhit ha ca cc hp cht mu

+ nh hng thnh phn nn ca mu

+ Mi trng tin hnh nguyn t ha mu.

+ Cht nn ca mu, cht ph gia thm vo.

Giai on lm sch Cuvet

Mc ch nhm lm bay hi cc cht bn nh cc kim loi hoc mui cn nm li trong ng graphite. C th thc hin 3000oC nhng nhiu trng hp cng thc hin nhit thch hp thp hn. Thng thng nhit lm sch s cao hn nhit nguyn t ha khong 2000C .

M t cc bc gia nhit trong GFA

Cc loi Graphite

Thng thng c 3 loi l Graphite

+ ng graphite High density

+ ng graphite Pyrolytic

+ ng graphite c Platform

Kiu ng graphit ti trong cao: Loai nay c s dung o hu ht cac nguyn t vi kt qua chinh xac va lp lai cao. Tuy nhin vi cac nguyn t d dang phan ng vi cacbon tao thanh cacbua kim loai, nhng hp cht nay khng bay hi hoan toan trong qua trinh nguyn t hoa lam giam .

Kiu ng graphit pyrolytic:

im khac bit vi kiu ng graphit ti trong cao la b mt cua ng graphit c trang mt lp Titan co th ngn chn phan ng gia cac nguyn t kim loai vi cacbon. Khi s dung h thng nay nhay co th tng t 2 n 3 ln so vi kiu ng graphit ti trong cao cho cac nguyn t Al,Si, cac nguyn t thuc nhom 4b,5b,6b,7b, (Ti,V,Cr,Mo,Fe,Co,Ni,Cu...) va cac nguyn t thuc ho lantan.Tuy nhin lp lai kem hn so vi kiu ng graphit ti trong cao.

Kiu ng graphit co san :San la 1 thanh cacbon co b day 1mm va din tich vai mm2 c t vao trong ng graphit.Vi kiu nay mu se c lam nong gian tip va ng u,lam giam anh hng cua cht nn va tin hiu nn.

Rt hiu qu phn tich cac nguyn t Cd, Pd va cac nguyn t co nhit si thp.

4.3.2.3 K thut hydride (Hydride Vapor Generator) Nguyn tc: K thut to hydride c mt im ging k thut ha hi ngui (Cool vapor) l mu c cho phn ng vi mt cht kh, sau kh sinh ra c dn n b phn hp thu o. Tuy nhin, khc vi k thut ha hi ngui, kh sinh ra khng phi l hi nguyn t t do m l hi phn t ca cc hp cht hydride. Cc phn t ny khng gy ra hp thu nguyn t nn cn phi cung cp nhit phn hy chng thnh cc nguyn t t do. K thut hydride c th c s dng phn tch cc nguyn t As, Pb, Sn, Bi, Sb, Te, Ge, Se.

Trc y s to thnh cc hp cht hidrua AsH3, SbH3 v H2Se trong dung dch thng c thc hin nhiu nht bng phn ng:

Zn + 2 HCl ZnCl2 + 2 [H] Em+ + (m+n) [H] EHn + mH+Trong : E l kim loi cn phn tch, m c th bng hoc khc n.

Nhng do phn ng trn c nhiu hn ch nh:

* Xy ra chm.

* Kh t ng ho.

* Kt qu phn tch ph thuc nhiu vo tinh khit ca km.

* Hiu qu phn ng b gii hn v phn ng xy ra khng hon ton v cc hp cht hidrua d bay hi b hp ph hoc b by trong lp mt km.

V th, thay cho qui trnh trn ngi ta s dng mt cht kh c hiu qu hn l NaBH4.

NaBH4 + 3 H2O + HCl H3BO3 +NaCl + 8 [H]

E+ + n[H] EHn

V d: Phn ng kh chuyn As (V) v As (III) trong qu trnh x l mu:

H3AsO4 + 3I- + 2H3O+ H3AsO3 + I3- + 3H2O

Phn ng vi cht kh NaBH4 H3AsO3 + BH4- + H+ AsH3 + H2O + H3BO3Phng php ny c s dng nhiu hn hn so vi phng php Zn/HCl do c th p dng vi nhiu nguyn t hn, do tc , hiu qu ca phn ng v gim c tp cht. Phn ng xy ra hon ton trong khong thi gian t 10- 30s. Tc cht c thm vo dung dch mu c acid ho trong khong t 0.1- 10%. Cc nhn t trn y gip cho s t ng ho d dng hn v l yu t quan trng to nn s thnh cng cho k thut to thnh cc hp cht hidrua. Acid dng cho qui trnh nu trn l HCl, HNO3 v H2SO4 cng c s dng. Nng ti u ca acid l mt thng s cho s ti u ho, n ph thuc vo nguyn t phn tch v cht nn.

Hn ch ca phn ng:

* Tc cht khng phi hon ton khng ln tp cht, lm nh hng n nhy gii hn pht hin.

* Lng ln kh H2 c phng thch cng gy cn tr.

u im:

k thut hydride c nhy cao v loi b c nh hng ca nn (matrix interference).

Nhc im:

- Hiu sut to hydride v nguyn t ha ph thuc mnh vo nhiu yu t bao gm trng thi oxi ha ca nguyn t cn phn tch, thi gian phn ng, p sut kh, nng axit v nhit ca b phn hp th.

- S to thnh hydride cng b nh hng bi cc cht trong thnh phn mu, do , k thut ny vn b nh hng v mt ha hc (chemical interference).

Cn nhiu

Trong giai on to hp cht hidrua, s cn nhiu c to nn do s c mt ca cc ion kim loi ngoi cht phn tch.

Cc nghin cu cho thy phng php phn tch bng k thut to hp cht hidrua cng chu s cn nhiu c giai on to hp cht hidrua v giai on nguyn t ho. S cn nhiu lm thay i tn hiu phn tch (thng l lm gim tn hiu).

Chng hn nh khi phn tch As v Se nu trong mu cn c cc ion kim loi chuyn tip khc nh Cu(II), Co(II), Ni(II)... th hiu sut to thnh cc hp cht hidrua vi cht phn tch s gim, ng thi cc tn hiu phn tch ca As v Se cng b che i. l do hidrua ca cht phn tch phn ng vi cc sn phm to thnh t phn ng ca cc kim loi vi NaBH4.

Tuy nhin cng c th gim nhiu bng cch thm NaBH4 vo t t vi nng thp. Trong h thng tim theo dng lin tc th s cn nhiu cng c gim thiu, do trong h thng ny hu nh khng c mt thi gian no m cht kh v sn phm phn ng hin din vi nng qu cao.

Khi phn tch cc nguyn t trong cc mu sinh hc, acid Nitric thng c dng ph mu v acid ho mu trc khi thm cht kh NaBH4 v iu ny gy nn vn l c s hin din ca cc oxit nit trong by nhit thp dng thu thp cc phn t cht hidrua lm gim hiu sut to hp cht hidrua.

khc phc hin tng ny ngi ta thm mt lng acid sunfamic khi ph mu. Trong giai on nguyn t ho, tn hiu phn tch thng b trit tiu do b mt ng nguyn t ho thch anh khng b thu tinh ho, v hoc b nhim bn do s tch t cc git cht lng nh b bm trn b mt ng.

Qu trnh nguyn t ho cng c th b dp tt nu c s hin din ca cc vt dung mi hu c.

Ngoi ra, hiu sut nguyn t ho cn gim st do s hnh thnh cc phn t bn nhit.

gim nhiu do nhng nguyn nhn trn, c th lm sch b mt ng nguyn t ho thch anh bng HF, tng nhit nguyn t ho bng cch s dng cc h thng nguyn t ho c nhit cao v tng nng cc gc hidro t do trong ng thch anh

Kt lun :

Phng php ny c nhy cao, gii hn pht hin thp, c th xc nh c cc nguyn t c hm lng rt nh (mg/l hoc g/l), c chn lc rt cao do mi kim loi hp th mt bc sng c trng do ngun bc x ngoi c to bng chnh nguyn t cn xc nh.

Khng cn tch cc cht, kim loi khc trong mu. V vy phng php AAS c s dng rt ph bin xc nh hm lng cc kim loi nng nh: As, Bi, Ge, Sb, Se, Te, Sn, Pb

Tuy nhin phng php ny c nhc im l khng th xc nh cng lc nhiu nguyn t, v th phng php ny tng i chm khi cn xc nh ng thi nhiu kim loi trong cng mt mu phn tch.

4.3.2.4 K thut ha hi lnh (Mercury Vapor Unit)

Gii thiu

- CV-AAS l phng php quang ph hp x nguyn t khng ngn la, s nguyn t ho thu ngn (Hg) c thc hin ngay ti nhit thng v Hg l nguyn t tn ti th lng v c th bay hi ti nhit phng. Nh c tnh ring bit ny nn Hg l nguyn t duy nht thch hp cho vic xc nh m khng cn nguyn t ho sau khi c kh ti trng thi c bn. V vy hu nh ton b hi thu ngn u tham gia vo qu trnh hp th.

- H thng CV - AAS c b ho hi lnh Hg gm cc bnh phn ng v h thng li cun hi thu ngn.

Nguyn tc

Trong k thut ha hi ngui, ion Hg2+ trong dung dch mu c kh thnh nguyn t t do bng cch cho phn ng vi mt cht kh mnh nh thic clorua (SnCl2) hoc natri tetrahydroborate (NaBH4) trong mt h thng kn. Sau , hi thy ngn t do c dn t bnh phn ng n b phn hp th bng cch sc mt dng kh mang thch hp, tr vi Hg (khng kh, nit hoc argon) vo dung dch mu. i khi b phn hp th c gia nhit cht t (khong 100oC) trnh ngng t hi nc.

Nu cht kh l SnCl2 th Hg2+ b kh theo phng trnh:

Sn2+ + Hg2+ Hg0 + Sn4+Nu cht kh l NaBH4 th Hg2+ b kh theo phng trnh:

Hg2+ + 2BH4- Hg0 + H2 + B2H6u im

- nhy ca phng php CV- AAS l ln hn khi so vi kt qu thu c t phng php F-AAS. C th hiu sut ly mu l 100% (so vi 10% ca k thut ngn la). Ton b Hg trong dng dch mu t trong bnh phn ng u c nguyn t ho v c vn chuyn n cell mu v o.

- nhy c th tng ln nh s dng cc mu c th tch ln hn v ton b hi Hg cha trong mu c gii phng o. Khi tng th tch mu th c ngha l c nhiu nguyn t Hg c hiu lc c chuyn di ti cell mu v o.

- Gii hn pht hin ca CV-AAS khong 0.02ug/L.

4.4. Phn tch nh lng bng AAS

Mu chun trong php o AAS

Trong phng php phn tch nh lng theo ph hp th nguyn t , mu chun dng ng chun cng bt buc phi tha mn mt s iu kin nht nh. Cc iu kin l:

1. Cc mu chun phi c trng thi vt l v ha hc nh mu phn tch, ngha l mu phn tch tn ti trng thi, dung mi, mi trng v dng lin kt no th mu chun cng phi c tnh cht ging nh th. C nh th mi loi tr c nh hng ca nn, v thnh phn ca mu n kt qu phn tch.

2. Cc mu chun v mu phn tch phi c pha ch, x l trong cng mt iu kin nh nhau.

3. Cc mu chun phi bn vng theo thi gian, ngha l khng b thay i thnh phn sau khi ch luyn v bo qun s dng lu di, khng b sa lng, khng b phn hy to thnh cc cht khc lm thay i thnh phn ca mu chun. C nh th mi bo m c thnh phn ca n nh tnh ton pha ch v s dng lu di.

4. Nng ca cc nguyn t cn phn tch trong cc mu u phi rt chnh xc theo yu cu ca phng php phn tch. ng thi khong nng ca mt dy mu u phi phn b u trong vng tuyn tnh hay trong ton b ng chu n ca php o v bao trm nng ca cc mu phn tch. Ngha l nng cc m u phn tch phi trong vng tuyn tnh ca ng chu n. Cn nu khng, chng ta phi pha long mu phn tch cho ph hp.

Cc phng php phn tch nh lng c th

xc nh nng (hm lng) ca mt nguyn t trong mu phn tch theo php o ph hp th nguyn t ngi ta thng thc hin theo cc phng php sau y:

1. Phng php ng chun;

2. Phng php thm tiu chun;

3. Phng php th khng i;

4. Phng php dng mt mu chun.

Phng php ng chun

Nguyn tc ca phng php ny l ngi ta da vo phng trnh c bn ca php o A theo nng mt dy chun (t nht l ba chun) dng mt ng chun v sau nh ng chun ny v gi tr Ax xc nh nng Cx ca nguyn t cn phn tch trong mu o ph, ri t tnh c nng ca n trong mu phn tch.

th chun ca ca phng php ng chun

Phng php ny n gin, d thc hin v rt thch hp vi mc ch phn tch hng lot mu ca cng mt nguyn t, nh trong kim tra cht lng thnh phm, kim tra nguyn liu sn xut. V mi khi dng mt ng chun chng ta c th xc nh c nng ca mt nguyn t trong hng trm mu phn tch. l u im ca phng php ny. Song trong nhiu trng hp chng ta khng th chun b c mt dy mu chun tha mn cc iu kin quy nh cho phng php nn khng xc nh c chnh xc v tr ca ng chun v nh th tt nhin kt qu phn tch s mc sai s ln. Ngha l khi mu phn tch c thnh phn phc tp v chng ta cha bit chnh xc th khng th chun b c mt dy mu chun ng n nn s b nh hng ca nn, ca thnh phn ca mu. chnh l nhc im ca phng php ny. Trong nh ng trng hp nh th, tt nht l dng phng php thm tiu chun xc nh nng ca nguyn t phn tch trong mu, hay bin i ca mu sang nn t to ph hp cho c mu u v cc mu phn tch.

Phng php thm tiu chun

Trong thc t phn tch, c bit l xc nh lng vt cc kim loi, khi gp phi cc i tng phn tch c thnh phn phc tp v khng th chun b c mt dy mu chun ph hp v thnh phn vi mu phn tch, th tt nht l dng phng php thm chun. Nh vy mi loi tr c yu t nh hng v thnh phn ca mu (matrix effect).

Nguyn tc ca phng php ny l ngi ta dng ngay mu phn tch lm nn chun b mt dy mu chun, bng cch ly mt lng mu phn tch nht nh v gia thm vo nhng lng nht nh ca nguyn t cn xc nh theo tng bc nng (theo cp s cng). V d lng thm vo l C1, C2, C3, C4, nh th chng ta s c mt dy chun nh trong bng sau, trong Cx l nng (hm lng) ca nguyn t cn xc nh trong mu phn tch.

Bng dy chun ca phng php thm tiu chu n.

th thu ng t phng php thm chun

xc nh Cx ta c th thc hin theo hai cch:

Cch I. Ko di ng chun v pha tri, n ct trc honh ti im Cx. on OCX chnh bng gi tr nng Cx cn tm.

Cch II. Cng c th xc nh Cx bng cch t gc ta k mt ng song song vi ng chun v t im Ao k ng song song vi trc honh, hai ng ny ct nhau ti im M, t im M h ng vung gc vi trc honh, ng ny ct trc honh ti im Co, chnh on OCX l bng gi tr Cx phi tm.

Phng php th chun c nh

Nguyn tc ca phng php ny l mun xc nh mt nguyn t no , trc ht ngi ta cng phi dng mt ng chun nh trong phng php ng chun. ng chun ny c gi l ng chun c nh (ng chun khng i) v ng chun ny c dng lu di. Nh vy mun xc nh c nng Cx cha bit, ngi ta ch vic thay gi tr Ax o c vo phng trnh tnh Cx

Hin nay phng php ny c s dng rng ri trong phng th nghim, cc thit b o c ci t sn phng trnh ng chun t tnh kt qu ca mu o. Tuy nhin cn phi kim tra nh k, v theo thi gian th iu kin hot ng ca my s khng cn ng nht gy ra s sau lch cho php o.

Phng php mt mu chun

+ Khi c mu chun

Trong nhng trng hp n gin, chng ta cng khng cn pha mt dy chun dng th chun, m c th tnh ngay gi tr Cx nh mt mu chun Cl ca cht phn tch. Ngha l chng ta c:

Vi mu phn tch: Ax = a.Cx (a)

Vi mu u: Ao = a.Cl (b)

Do em (a) chia cho (b) chng ta c: C: (Ax/Ao).Cl.

Nh vy khi o c gi tr Ax v Ao ta c t s ca chng, v ch vic nhn n vi gi tr C1l chng ta c gi tr nng Cx phi tm theo biu thc trn.

+ Khi khng c mu chun

Trong trng hp ny, chng ta cng khng cn pha mt dy chun dng th chun, m dng ngay 1 mu phn tch lm nn chun b mt mu phn tch v1mu thm chun theo phng php thm chun v tnh ngay gi tr Cx nh mt lng chun C1 ca cht phn tch c thm vo. Ngha l chng ta c:

Vi mu phn tch khng thm chun: Ax = a.Cx (a)

Vi mu u phn tch c thm chun: Ach= a.(Cx+ Cl) (b)

Do ly (a) chia cho (b) chng ta c: Cx = [Ax /(Ach-Ax)]. C1

Nh vy khi o c gi tr Ax v Atch ta tnh c nng Cx phi tm theo biu thc trn.

Nhng mt iu phi ch l nng thm vo Cl v cc gi tr Cx phi nm trong vng tuyn tnh ca phng php.

4.5. ng dng quang ph AAS trong phn tch thc phm

4.5.1 Xc nh mt s nguyn t vi lng (Fe, Cu, Zn) trong rau qu bng AAS (F AAS).

4.5.2 Xc nh ch, cadmium, km, ng v st trong thc phm bng ph AAS ( AOAC 999-116)

4.5.3 Xc nh Cd trong thc phm bng k thut nguyn t ho ngn la (FAAS) AOAC 973-34

4.5.4 Xc nh thu ngn trong thc phm bng FAAS ( 971-21)

4.5.5 Xc nh Cadmium, chromium, copper, iron, lead, magnesium, manganese, silver, zinc trong thc phm bng AAS (AOAC 974-27)

4.5.6 Xc nh Nickel trong Tea Atomic Absorption Spectrophotometric Method (AOAC 975-34)

4.5.7 Phn tch Pb trong Milk bng ph AAS )

CHNG IV

PHNG PHP CHUN IN TH

4.1.C s ca phng php chun in th

4.1.1.nh ngha: phng php chun in th mt phng php phn tch da trn vic o s bin thin th trong sut qu trnh chun dung dch nghin cu.

4.1.2.t im ca phng php

- Trong sut qu trnh chun th dung dch thay i, s thay i xy ra t ngt ti thi im st trc v st sau im tng tng. - Cn chn in cc thch hp vi loi phn ng chun .

u im so vi phng php ha hc l:

+ nhy cao c th ln ti 10-5mol+ Chun c nhng dung dch c mu+ Chun nhng trng hp khng c cht ch th

4.1.3. Pin

Pin in ha

Gm mt bnh in phn c phn lm hai phn. Mt bn cha dung dch CuSO4 trong c nhng in cc Cu, mt bn th cha dung dch ZnSO4 v c nhng in cc Zn. Khi ni 2 in cc i qua mt in k G, ngi ta thy mt s hin tng nh sau :

- Kim in k G ch chiu dng in i t Cu sang Zn

- Khi lng Zn gim, khi lng Cu tng

- [ZnSO4] tng , [CuSO4] gim

Nguyn nhn ny c gii thch nh sau :

Dng in i t cc Cu sang Zn => dng in t s i t cc Zn sang Cu. Cc Zn cho in t , cc Cu nhn in t. Suy ra: Zn 2e Zn2+ qu trnh lm cho [ZnSO4]tng -> m Zn gim

Cu2+ + 2e Cu. ng sinh ra kt tinh ln cc Cu lm khi lng Cu tng , [CuSO4] gim

Tng hp cc phn ng 2 in cc ta c :

Cu2+ + Zn Cu + Zn2+

Phn ng ny chuyn ha nng thnh in nng, v h hot ng nh vy gi l h pin

Zn/ ZnSO4 // CuSO4 /Cu

Hay:Zn/ Zn2+ // Cu SO4 /Cu

4.1.4.Th in cc

Kho st 1 thanh kim loi nhng trong mt dung dch in ly, nh vy s c s tip xc b mt thanh kim loi vi dung dch. S tip xc ny sinh ra mt s chuyn di cation t thanh kim loi i vo dung dch hay t dung dch kt tinh ln b mt kim loi.

* TH1 : Khi th mt lng cation kim loi c xu hng bc khi b mt i vo dung dch.

Khi cation kim loi bc khi b mt i vo dung dch in t li trn b mt kim loi lm b mt tch in (-), b mt tch in (-) c xu hng ht cc cation ln b mt ca n to nn lp in kp v hnh thnh th in cc.

* TH2:Ngc li th cation trong dung dch s kt tinh ln b mt kim loi, s kt tinh ca cc cation kim loi lm b mt kim loi tch in (+) v c xu hng ht cc anion ti b mt ca n v sinh ra th in cc. xc nh gi tr ca th in cc ngi ta khng th xc nh gi tr tuyt i ca n m ch xc nh gi tr tng i qua th c gia 2 in cc ch khng th xc nh th ca mi in cc. V vy trong k thut xc nh gi tr ln, nh v th ngi ta phi chn mt th in cc chun v t cho n mt gi tr , cc in cc khc s c gi tr sau khi so snh vi n, in cc ngi ta chn l in cc Hydro v xem E02H+/H2 = 0

Cch xc nh th tiu chun : Th tiu chun l th c xc nh trong iu kin tiu chun 250C- 1atm

V d 1: Xc nh = ?

E = E0Cu2+/Cu E02H+/H2

Chiu dng in chy t cc Cu n cc Hydro

Lp pin nh sau : (Pt)H2/ H+//Cu2+ /Cu

Theo thc nghim o c E= 0,34V. V E02H+/H2 = 0

Suy ra :E0Cu2+/Cu = 0,34V

V d 1: Xc nh E0Zn2+/ZnThc nghim o c: E= 0,77V

Chiu dng in chy t cc Hydro n cc Zn

Lp pin nh sau: Zn/Zn2+//H+/(Pt)H2

M :E = 0,77V = E02H+/H2 - E0Zn2+/Zn = 0,77v

Suy ra : E0Zn2+/Zn = - 0,77v

Gi tr th ca cc cp oxy ha kh

Th tiu chun

Gi tr th o c gia kim loi v dung dch mui ca n c xc nh bng phng trnh Nerst

Trong E0 l th tiu chun ca kim loi

iu kin chun 250C, 1at th phng trnh c vit li nh sau :

V d: i vi cp Fe3+/ Fe2+

i vi cp Cu2+/ Cu

V kim loi Cu lm in cc nn c th xem hot ca n khng i v vy c th vit li nh sau :

Th thc

Thc t th th o c ca mt cp oxy ha kh khng ch ph thuc vo bn cht kim loi lm in cc v nng ion ca n m cn ph thuc vo cc yu t khc nh mi trng m chng tn ti

V d nh phn ng c s tham gia ca cc ion H+ vo qu trnh oxy ha kh : MnO4- + 5e + 8H+ = Mn2+ + 4H2O

Ta thy lc ny th c tnh nh sau:

Hay xt phn ng : Cr2O72- + 6e + 14H+ = 2Cr3+ + 7H2O

Th lc ny c tnh nh sau :

Th cn bng

Trong phng php chun in th, qu trnh kho st phn ng xy ra khi chun chnh l kho st s bin thin th sinh ra gia cc cp oxy ha kh tham gia phn ng. Trong qu trnh cht ng vai tr oxy ha s tham gia vo qu trnh kh v nhn in t lm cho gi tr th ca n gim xung cn cht ng vai tr cht kh s tham gia vo qu trnh oxy ha, cho in t lm cho th ca n tng ln. Khi th ca hai cp oxy ha kh bng nhau th qu trnh chm dt. Th o c ti thi im gi l th cn bng .

Nh vy th cn bng l th m ti cht oxy ha phn ng va vi cht kh trong qu trnh chun .

V d: xt qu trnh phn ng xy ra trong h gm mt thanh Pt nhng trong dung dch Fe2+ v Fe3+ c nng bng nhau. Cng trong iu kin y trong dung dch Cu2+ v Cu+ . Ngi ta ni hai in cc qua mt b phn o th quan st s bin thin ca th t trong qu trnh.

Phn ng chun xy ra nh sau :

Fe3+ + Cu+ = Cu2+ + Fe2+Lc ny th ca cc Fe c tnh nh sau :

Th ca cc Cu : Qu trnh phn ng lm sinh ra Fe2+ nng Fe2+ tng dn n th cc Fe gim.

Ngc li nng Cu2+ tng nn th cc Cu tng

Khi EFe = ECu ta c ECB =