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<p>M UCc phng php phn tch bng cng c c vai tr c bit quan trng trong s pht trin ca cc ngnh khoa hc k thut v cng ngh. Vi s pht trin nhanh chng ca k thut in t v tin hc, cc my mc thit b phn tch cng c hin i ha, cho php xc nh nhanh chng vi chnh xc cao cc mu cha hm lng rt nh ca cc cht phn tch. Nhm cc phng php phn tch quang hc da trn cc tnh cht quang hc ca cht cn phn tch, c mt s phng php sau: 1. Phng php trc quang da trn php o lng bc x in t ( bxt ) do dung dch phn tch hp th. y cn k n phng php hp c, da trn php o lng bxt b hp th bi cc ht huyn ph (dung dch keo); Phng php khuych c, da trn php o lng bxt b khuych tn bi cc ht huyn ph. 2. Phng php quang ph pht x nguyn t AES (Atomic Emision Spectrometry), da trn s kho st ph pht x nguyn t ca nguyn t cht phn tch. 3. Phng php quang ph hp th nguyn t AAS (Atomic Absorption Spectrometry), da trn s kho st ph hp th nguyn t ca nguyn t ca cht phn tch. 4. Phng php pht quang, da trn php o cng bc x do cht phn tch pht ra, di tc dng ca nng lng bxt chiu vo n. Ngoi ra, thuc vo cc phng php quang hc cn c phng php khc x, da trn php o chit sut ca cht phn tch; Phng php ph hng ngoi IR, Phng php ph Rntgen; Phng php ph Raman</p> <p>1</p> <p>CHNG 1. CC VN CHUNG1.1. Bn cht ca bc x in t v cc phng php ph 1.1.1. Bn cht ca bc x in t Bc x in t ( bxt ) bao gm t sng v tuyn n cc bc x Rntgen v Gamma u c bn cht sng v ht. Bn cht sng ca bxt th hin hin tng nhiu x v giao thoa, bxt l nhng dao ng c hai thnh phn l in trng v t trng, cc sng ny truyn i trong khng gian vi vn tc ca nh sng theo hnh sin c cc cc i v cc tiu; khong cch gia 2 u mt ca mt sng c gi l bc sng, k hiu . Cng ca bxt t l vi bin ca dao ng. Nhng bxt khc nhau c di bc sng khc nhau hay bc sng l i lng c trng cho bxt. Ngoi ra bxt cn c c trng bng tn s , gia bc sng v tn s lin h vi nhau qua biu thc: c= hay = c / trong c l tc nh sng, c = 3.108 m/s Trong cc phng php ph, ngi ta cn dng i lng nghch o ca ( 1/ ) gi l s sng c trng cho sng, n v ca s sng lun l cm-1 = 1/ photon, cc dng bxt t khc nhau c nng lng khc nhau. S thng nht gia bn cht sng v bn cht ht ca bxt c th hin trong biu thc: = h = hc/ trong h l hng s Planc, h = 6,62.10-34J.s 1.1.2. n v o v s phn chia cc vng bxt Trong biu thc 1.4 l cc i lng c trng cho bxt. Bc sng c th nguyn l di. o , ngi ta dng cc n v o di l mt (m) cng cc c s ca mt, cc n v hay dng l m; nm v Ao ( 1A = 10-10m ).2</p> <p>(1.1) (1.2)</p> <p>( 1.3)</p> <p>Vi bn cht ht, bxt l nhng phn nh mang nng lng c gi l</p> <p>(1.4)</p> <p>i lng nghch o ca bc sng l s sng ch o bng mt loi n v l cm-1. Tn s c nh ngha l s dao ng m bxt thc hin trong mt giy, nn c th nguyn l s-1. n v o ca l hec ( hertz ) c k hiu l Hz v cc bi s ca n l kHz ( kilohec ); MHz ( megahec ). c th gy hiu ng quang ph, nng lng ca bxt phi ph hp vi hiu s mc nng lng E tng ng vi cc trng thi nng lng ca nguyn t hay phn t, ngha l bc sng ca bxt phi ph hp vi h thc: E = = h = hc/ hay = hc/E phn tch m ta c cc phng php quang ph khc nhau, c th l: - Min sng v tuyn, viba cho phng php ph cng hng t. - Min sng tia Rntgen v tia cho cc phng php ph Rntgen v ph tia . - Min sng nh sng quang hc cho cc phng php ph nhn thy ph t ngoi ( UV - VIS ); ph hng ngoi ( IR ). - Trong min sng nh sng quang hc cng c cc phng php ph pht x nguyn t; ph hp th nguyn t v ph hunh quang. Di y l cc vng sng chia theo chiu di bc sng. Bng 1.1. Phn loi cc vng bc x in t Bc x Tia Tia Rntgen T ngoi v kh kin Hng ngoi Vi sng Sng v tuyn , cm 10-11 - 10-8 10-8 - 10-6 10-6 - 10-4 10-4 - 10-2 10-1 - 10 &gt; 10 E, eV ~ 107 ~ 105 ~ 10 ~ 10-1 ~ 10-3 &lt; 10-6 ( 1.5) Ty theo bn cht ca bxt tng tc vi nguyn t hay phn t ca cht</p> <p>1.2. S tng tc gia vt cht v bxt3</p> <p>Khi chiu mt chm bxt vo mt mi trng vt cht, s xy ra hin tng cc phn t hay nguyn t ca vt cht hp th nng lng hay pht x nng lng. Nng lng m phn t hay nguyn t pht ra hay hp th vo l: E = E2 - E1 = h s ca bxt b hp th hay pht x ra. Nu nng lng trng thi cui cao hn trng thi u ( E &gt; 0 ) th xy ra s hp th bxt, ph sinh ra trong qu trnh ny l ph hp th; Cn nu nng lng trng thi u cao hn trng thi cui ( E &lt; 0 ) th xy ra s pht x nng lng, ph sinh ra trong qu trnh ny l ph pht x. Cc phng php phn tch da vo ph nguyn t thc hin trn cc my quang ph hp th nguyn t AAS hay my quang ph pht x nguyn t AES. Cc phng php phn tch da vo ph phn t th phong ph hn, thc hin trn cc my o quang UV-VIS; my quang ph hng ngoi IR. 1.3. Trng thi nng lng ca phn t, ph phn t Mt phn t d l n gin nht cng c cc chuyn ng sau: - Chuyn ng ca cc in t quanh cc ht nhn: cc in t ha tr v cc in t khng tham gia to lin kt ha hc - gi chung l chuyn ng in t. - Chuyn ng thay i tun hon cc v tr ca cc ht nhn so vi nhau gi l chuyn ng dao ng ca phn t. - Chuyn ng thay i phng hng ca ton phn t trong khng gian - gi l chuyn ng quay ca phn t, chuyn ng ny ch c cc phn t cc cht trng thi kh v hi. Nh vy, nng lng ton phn Etf ca phn t c th biu din: Etf = Ee + Ev + Er lng in t. Ev l nng lng lin quan n chuyn ng dao ng ca ht nhn ( vibration ) - gi l nng lng dao ng.4</p> <p>( 1.6 )</p> <p>Trong E1 v E2 l mc nng lng trng thi u v trng thi cui; l tn</p> <p>( 1.7 )</p> <p>trong : Ee l nng lng lin quan n chuyn ng ca in t - gi l nng</p> <p>Er l nng lng lin quan n chuyn ng quay ca phn t ( rotation ) - gi l nng lng quay. L thuyt v thc nghim chng minh Ee &gt;&gt; Ev &gt;&gt; Er , nu nng lng o bng n v kcal/mol th Ee khong 60 150 kcal/mol; Ev khong 1 10 kcal/mol; Er khong 0,01 0,1 kcal/mol. Trong iu kin bnh thng, cc phn t tn ti trang thi c bn, c nng lng thp nht Eotf, khi phn t nhn nng lng, v d khi hp th bc x, c th chuyn ln mc nng lng cao hn. Khi phn t nhn nng lng ln, v d bxt c nng lng ln, phn t chuyn ln trng thi c nng lng cao hn E*tf gi l trng thi kch thch v: E*tf = E*e + E*v + E*r phn t. Etf = E*tf - Eotf = Ee + Ev + Er ( 1.9 ) Etf l bc chuyn nng lng ton phn ca phn t; Ee l bc chuyn nng lng in t; Ev l bc chuyn nng lng dao ng; Er l bc chuyn nng lng quay. Nh vy do hin tng hp th bxt ca phn t gy nn cc bc chuyn nng lng in t, nng lng dao ng, nng lng quay ca phn t, l ngun gc cc loi ph hp th phn t: ph quay, ph dao ng - quay, ph in t - dao ng - quay.... Ngoi ra, phn t c th hp th cc bxt gy nn cc bc chuyn nng lng, ngoi vic cn c iu kin nng lng ph hp theo h thc ( 1.5 ) cn c cc yu cu khc, gi l theo quy tc chn lc. C hai loi quy tc l quy tc cho php v quy tc cm: quy tc cho php quy nh cc iu kin cho php xy ra cc bc chuyn; Quy tc cm nu cc iu kin m vi cc iu kin bc chuyn nng lng khng xy ra c. Chnh v bn cht nh vy m ph phn t c cu trc rt phc tp, chng ta thng ni l c cu trc m. Vi cc my quang ph c tn sc khng ln, ph phn t hu nh l min bc x lin tc; Vi cc my quang ph c tn sc ln ph phn t gm v s vch st nhau. (1.8 ) S thay i trng thi ca phn t do c s thay i v nng lng ca</p> <p>5</p> <p>Mi phn t ca mt cht th c cu trc khc nhau nn c cc bc chuyn nng lng khc nhau, s c ph hp th phn t c trng v khc nhau, mt khc vi cc k thut ph hp, ngi ta to ph in t, ph dao ng, ph quay ca phn t ca cht nghin cu, chnh l c s ca cc phng php phn tch nh tnh. Cn phn tch nh lng, ngi ta da vo nh lut v s hp th bxt Lambert-Beer . 1.4. Ph hp th nguyn t v ph pht x nguyn t trn ta xt s to thnh ph ca phn t, to bi s lin kt ca t nht l hai nguyn t. Cn khi l nguyn t trng thi hi t do th s c trng bi ph hp th hoc ph pht x nguyn t, c ch to thnh c th gii thch nh sau: Trong iu kin bnh thng nguyn t trng thi c bn, khng thu v cng khng pht nng lng di dng cc bc x. y l trng thi bn vng v ngho nng lng. Nu nguyn t nhn nng lng di dng nhit th nguyn t s chuyn ln trng thi c nng lng cao hn, gi l trng thi kch thch, trng thi kch thch ny khng bn, ch khong 10-8 10-9 s, sau nguyn t c xu hng tr v trng thi c mc nng lung thp hn, khi ny nguyn t s gii phng nng lng di dng bxt bao gm nhiu tia n sc c bc sng khc nhau nm trong di ph quang hc ( 190 - 1100nm ). Nu thu, phn li v ghi chm tia ta s c di ph gm cc vch pht x ca nguyn t hoc ion. Trong tp hp cc vch ph th mi nguyn t hoc ion li c nhng vch c trng ring. Mt c im quan trng l cc nguyn t t do c kh nng hp th nhng tia bc x m n c th pht ra trong qu trnh pht x ca n. Nu nguyn t nhn nng lng di dng bxt ng ng vi nhng tia m n pht ra trong qu trnh pht x th nguyn t chuyn ln trng thi kch thch. Ph sinh ra trong qu trnh ny gi l ph hp th nguyn t. Nu gi nng lng ca bxt b nguyn t hp thu l = h th ta c: = h = E = Em - Eo hay E = h.c/ ( 1.10 ) (1.11 )</p> <p>6</p> <p>Trong Em v Eo l nng lng trng thi kch thch v trng thi c bn ca nguyn t; h l hng s Planck; c l tc nh sng; l bc sng ca vch ph hp th. Vy ph hp th nguyn t cng l ph vch. Nhng nguyn t khng hp th tt c cc bc x m n c th pht ra c trong qu trnh pht x. Qu trnh hp th ch xy ra vi cc vch ph nhy, cc vch ph c trng v cc vch ph cui cng ca nguyn t. Cho nn i vi cc vch ph qu trnh hp th v pht x l hai qu trnh ngc nhau. Trong phng trnh ( 1.10 ), nu gi tr E l dng ta c qu trnh pht x, nu gi tr E l m ta c qu trnh hp th. Nh vy ty theo tng iu kin c th nguyn t ha mu v kch thch nguyn t m qu trnh no xy ra l chnh, c th l: - Nu kch thch nguyn t bng nng lng nhit ta c ph pht x nguyn t. - Nu kch thch nguyn t bng chm tia n sc ta c ph pht x nguyn t. Phng php phn tch da trn ph pht x nguyn t gi l phng php quang ph pht x nguyn t AES (Atomic Emision Spectrometry ) vi my phn tch tng ng. Phng php phn tch da trn ph hp th nguyn t gi l Phng php quang ph hp th nguyn t AAS ( Atomic Absorption Spectrometry ) vi cc my phn tch AAS.</p> <p>7</p> <p>Chng 2. PHNG PHP QUANG PH HP TH PHN T UV-VIS(Phng php trc quang phn t) Phng php quang ph hp th phn t hay cn gi l phng php o quang, phng php phn tch trc quang phn t l mt trong nhng phng php phn tch cng c thng dng vi rt nhiu th h my khc nhau, t cc my n gin ca th h trc cn c gi l cc my so mu n cc my hin i c t ng ha hin nay, gi l my quang ph hp th phn t UVVIS. Cc my o quang lm vic trong vng t ngoi (UV) v kh kin (VIS) t 190nm n khong 900nm. 2.1. C s l thuyt ca phng php 2.1.1. S hp th nh sng ca dung dch mu Dung dch c mu l do bn thn dung dch hp th mt phn quang ph ( mt vng ph ) ca nh sng trng, phn cn li l ra cho ta mu ca dung dch, chnh l mu ph ca phn nh sng trng b hp th (vng quang ph cn li). V d: dung dch Fe(SCN)3 ta nhn thy mu l do khi nh sng chiu vo dung dch, dung dch ny hp th mnh bc x n sc mu xanh v xanh l cy, vng quang ph cn li l ra cho ta mu . S hp th ca dung dch theo mu c trnh by trong bng 2.1 Bng 2.1. S hp th mu ca cc dung dch mu TIA SNG N SC B HP TH 400nm 450nm: vng tm 450nm 480nm: vng chm 480nm 490nm: vng chm lc 490nm 510nm: vng lc chm 510nm 560nm: vng lc 5600nm 575nm: vng lc nh vng MU CA DUNG DCH lc nh vng vng da cam ta tm</p> <p>8</p> <p>575nm 590nm: vng vng 590nm 640nm: vng da cam 640nm 720nm: vng 720nm 800nm: vng ta</p> <p>chm chm lc lc chm lc</p> <p>S hp th bc x n sc (bxs) ca dung dch cn ph thuc vo nng ca cht hp th. v d trn, dung dch Fe(SCN)3 c nng cng ln th s hp th cng mnh, biu hin mu ca dung dch cng m. 2.1.2. Cc nh lut c bn v s hp th nh sng nh lut Bug - Lambe (Bourguear - Lambert): Khi chiu mt chm bxs c cng I0 qua mt lp vt cht c b dy l, th cng bxs l ra I bao gi cng nh hn I0 . C th biu din bng biu thc: I0 = I + Ia + Ir Trong : Ia l phn cng b hp th Ir l phn cng b phn x li I l phn cng l ra Da vo v s thc nghim, hai nh bc hc a ra nh lut hp th nh sng, biu din bng biu thc: I = I0 . e-kl cht v vo bc sng ca bxs. nh lut Lambe - Bia ( Lambert - Beer): Khi p dng nh lut Bug - Lambe cho trng hp vt cht l dung dch c dy l ( dung dch ng trong cuvt c dy l ) cha cht hp th c nng C. Nh bc hc Bia a ra nh lut Lambe - Bia: - Ni dung: Vi cng b dy ca lp dung dch, h s hp th k t l vi nng ca cht hp th ca dung dch. - Biu thc: k = *.C hay I = I0 . e-*C.l9</p> <p>(2.1)</p> <p>(2.2)</p> <p>Trong k l h s hp th, gi tr ca k ph thuc vo bn cht ca vt</p> <p>(2.3) (2.4)</p> <p>Nu i logarit t nhin v logarit thp phn th biu thc ca nh lut Lambe - Bia c th biu din bng biu thc: I = I0 . 10-.l.C Trong : C- l nng dung dch, o bng mol/l l - l b dy ca cuvt ng dung dch, o bng cm - c gi l h s tt phn t hay h s hp th phn t. l i lng xc nh, ph thuc vo bn cht ca cht hp th, vo bc sng ca bxs v vo nhit . 2.1.3. Cc i lng hay s dng Biu thc ( 2.5 ) chnh l c s cho phng php phn tch nh lng. Tuy nhin, quan h gia cng nh sng v nng ca dung dch thng qua hm logart, thun tin cho s dng, chng ta thng s dng cc i lng sau: truyn quang T: l t l gia cng chm sng n sc sau khi i qua dung dch I vi cng chm sng n sc chiu vo I0. T = I/I0 = 10-.l.C Nu l = 1cm th T gi l h s truyn quang. Trn cc my phn tch, T thng c biu din bng %, Thang o T t 0 100 Mt quang D (Dentisity) hay hp th A (Absorption) hay tt E (Extinction): c nh ngha theo biu thc sau D = A = E = - lg T = lg(I0 /I) = .l.C Vi cc dung dch cha cht hp th xc nh, ng trong cc cuvt c kch thc nh nhau th v l l khng i, khi ny c th biu din: D = A = K.C (2.7) Hay ni cch khc, s ph thuc gia mt quang v nng dung dch l tuyn tnh, chnh l c s ca phng php phn tch nh lng trc quang phn t. Nh vy nguyn tc chung ca phng php o quang xc nh mt cht X no , ta chuyn n thnh mt cht c kh nng hp th nh (2.6) (2.5)</p> <p>10</p> <p>sng ( bxs ) ri o s hp th nh sng ca n v suy ra hm lng cht cn xc nh. Tuy nhin c th p dng biu thc ny i hi phi cp n cc yu t nh hng. 2.1.4. Tnh cht ca mt quang v ng dng trong ha phn tch Biu thc D = A = .l.C cng c th coi l ni dung ca nh lut Lambe - Bia. Nu ta o mt quang ca dung dch c nng 1mol/l ng trong cuvet c b dy 1cm th gi tr mt quang o c chnh l h s hp th phn t, = D, y chnh l ngha vt l ca h s hp th phn t ca mt cht nht nh; ph thuc vo bn cht ca cht hp th nh sng v vo bc sng ca bxs c hp th. o mt quang ca dung dch bng mt cuvt (l, C = const) cc bc sng khc nhau th ta c ng cong biu din ph hp th ca dung dch, D = f() hay = f().</p> <p>Hnh 2.1. Dng ng cong hp th D = f()11</p> <p>o mt quang ca mt dy dung dch c nng khc nhau bng mt cuvt ti mt bc sng nht nh ( l, = const ) th ng biu din D = f(C) s l ng thng.Mt quang</p> <p>D6 D5 D4 D3 D2 D1</p> <p>C1 C2 C3 C4</p> <p>C5</p> <p>C6</p> <p>Nng </p> <p>Hnh 2.2. Dng ng biu din D = f(C) Mt c tnh rt quan trng ca mt quang l tnh cng tnh, c th chng minh nh sau: Gi s c mt chm bxs c cng I0 i qua 2 dung dch c b dy l1 v l2 tng ng vi cc nng C1, h s tt 1 v C2, h s tt 2 D = lg(I0 /I2 ) = lg(I0 /I1 ) + lg(I1 /I2 ) = D1 + D2 = 1.l1.C1 + 2.l2.C2 Nh vy mt quang ch ph thuc vo s cc phn t hp th nh sng nm trn ng nh sng truyn qua. Trong dung dch c nhiu cht tan hp th bxs th mt quang o c chnh l tng cc mt quang ca cc cht c trong dung dch, D = Di. Khi mun o mt quang ca cht phn tch trong dung dch c nhiu cht th phi loi tr mt quang ca cc thnh phn cn li, chnh l mt quang ca dung dch trng hay dung dch so snh. Dung dch trng hay dung dch so snh l dung dch cha tt cc cc thnh phn trong dung dch phn tch tr cht phn tch. Trong thc t, nhiu khi hp th ca dung dch so snh rt nh, khng ng k th ngi ta c th thay bng nc ct.12</p> <p>2.2. Cc iu kin ti u cho mt php o quang Ta bit D = f(,l,C) v theo nh lut Lambe - Bia khi 2 i lng ,l khng i th s ph thuc D = f(C) l tuyn tnh, phi c dng y = ax l mt ng thng, y cng chnh l c s ca phng php phn tch nh lng. Nh vy nhng yu t nh hng n s hp th nh sng l bc sng ca nh sng ti v cc yu t gy nh hng ti nng C c th lm sai lch nh lut Lambe - Bia gy sai s cho php phn tch, v vy ta phi c bit ch n cc yu t ny. 2.2.1. S n sc ca ngun bxt Gi s chm sng ti c cng I0 khng phi l tia sng n sc m l mt chm tia c cng I01, I02, I03 v cht phn tch ch hp th tia th 2 cn khng hp th tia 1 v tia 3, khi ny D = lg( I0 /I) = lg( I01+ I02+ I03)/I0...</p>