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TIU CHUN VIT NAM TCVN 2620-1994

Sot xt ln 1

UR NNG NGHIP

PHNG PHP TH

Urea for agriculture

Method of test

1. Ly mu

1.1. Tu theo yu cu c th, c th ly mu kho, trn toa xe, trn dy chuyn sn xut hoc ti cc imbn sn phm. Mu c ly theo l hng

1.2. Ly mu trong kho .

Dng c lymu l mt ng kim loi khn g, c dng lng mng. Dng c ly mu khng c lm nhhng n cht lng ca ure v c th ly c mu cc v tr tu trong bao.

Chn ngu nhin 1 % s bao cc lp trn, gia v di l v tin hnh ly mu tng bao vi mt lngmu sao cho tng lng mu ly c tt c cc bao khng c t hn 7 kg.

1.3. Ly mu trn toa xe. Chon ngu nhin 4- 5 toa xe, mi toa xe ly 3 % s bao. Tin hnh ly mu tngbao vi mt lng mu ly c khng t hn 7 kg

1.4. Ly mu trn dy chuyn sn xut. Mu c ly t ng theo cc klhong thi gian bng nhau vi mtlng mu bng nhau sao cho lng mu ly c trong mt gi t t 1-3 kg.

1.5. Ly mu ti im bn sn phm

Tin hnh theo iu 1.2 ca tiu chun ny

1.6. Mu ly c em trn u sau nhnh chng rt gn theo phng php chia t. B hai phn idin, hai phn cong li trn u v lp li qu trnh trn cho n khi lng mu hai phn cn li khong 1 -2 kg.

1.7. Cho mu vo hai l thu tinh kh, sch hoc bao cht do dn kn. Mt l hoc bao em phn tch, lhoc bao cn li lu. Trn l hoc bao phi dn nhn ghi r:

Tn c s sn xut

Tn sn phm

Lng mu

Ni ly mu

S hiu mu v l hng

Ngy, thng ly muTn v ch k ngi ly mu

1.8. L hng l lng sn phm c cng ch tiu cht lng c cha trong cng mt loi bao gi v giaonhn trong cng mt t. Mi l hng khng qua 200 T v phi km theo mt giy chng nhn cht lng do

phng KCS ca c s sn xut cp

1.9. Giy chng nhn cht lng phi bao gm cc ni dung sau:

Tn c s sn xut

Tn sn phm

Cc ch tiuc ht lng

Khi lng l hng

Ngy thng sn xut

S hiu tiou chun

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2. Phng php th

2.1. Qui nh chung

2.1.1 Nu khng c ch dn no khc thuc th dng trong cc php phn tch phi l loi TKPT hoc tngng

2.1.2 Nc ct theo TCVN 2117-77 hoc nc ct c tinh khit tng ng

2.1.3 Mi php th phi tin hnh song song trn hai mu cn, sai s gia hai ln xc nh song song khngc ln hn 0,2 % gi tr tuyt i

2.1.4 Sau khi th, nu mt trong cc ch tiu khng t tiu chun th phi tin hnh phn tch li vi lngmu gp i ly cng l hng, kt qu phn tch li l kt qu cui cng.

2.2Xc nh cc ch tiu ngoi quan

Cc ch tiu ngoi quan ca ure c kim tra bng phng php trc quan theo cc yu cu qui nh trongim 1 bng 1 TCVN 2619-1994.

2.3. Xc nh hm lng nit

2.3.1 Phng php th tch sau khi chng ct ( phng php trng ta)

2.3.1.1. Nguyn tc ca phng php

Bin i nitoe trong mu th thnh nit dng amoni khi c mt cht xc tc bng cch un nng trongdung dch axit sunfuric m c. Chng ct v hp th amoni trong mt lng dung dch axit sunfuric chun dv chun ngc bng dung dch natri hidroxit chun vi s c mt ca cht ch th

2.3.1.2 Thuc th

- Nc ct

- ng (II) sunfat kt tinh ( CuSO4. 5H2O);

- axit sunfuric,d= 1,84 g/ml tng ng vi dung dch 96 % hoc khong 36 N

- natri hidroxit, dung dch 450 g/l;

- axit sunfuric, dung dch chun 0,5 N

- natri hidroxit, dung dch chun 0,5 n

- hn hp ch th trong etanol : ho tan 0,1 g metyl trong khong 50 ml etanol 95 % ( V/ V) v thm0,05 g metylen xanh. Sau khi ho tan, pha long bng etanol n 100 ml v khuy u.

2.3.1.3 Dng c

Cc dng c trong phng th nghim v bnh Kendan, dung tch 500 ml c nt y thch hp

Dng c chng ct vi phn ni c mi hoc l mt dng c bt k m bo chng ct v hp th mtcch nh lng. V d nh dng c cho trn hnh 1 gm:

- bnh ct A dung tch 1000 ml c phn ni c mi

- u trnh bng B c phn ni vc u vo v u ra song song c lp vi phu nh git C dnghnh tr, dung tch 50 ml

- ng sinh hn Libic D chiu di s dng khong 40 mm, khp vi van kho khng mi u vo vvan mi u ra

- bnh nn E dung tch 500 ml, c dui ni c lp vi hai bu qu l

- kp l xo F

2.3.1.4 Chun b mu th

a) mu th : cn khong 5 g mu th vi chnh xc 0,001 g v cho vo bnh Kendan

b) Mu trng: tin hnh lm mu trng ng thi trong cng mt thi gian lm mu th, theo cng mt

hnh tr v s dng cng mt lng tt c cc thuc th nh s dng khi lm mu th, nhng khng c muth.

c) Tin hnh xc nh

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chun b dung dch mu: Thm vo bnh Kendan ( 2.3.1.3 ) cha mu th ( a) 25 ml nc, 50 ml dung dchaxit sunfuric d= 1,84 g/ml v 0,75 g ng sungfat. y bnh Kendan bng nt hnh qu l v cn thn un nngcho n khi ho tan ton b cacbon dioxit

Bnh Kendan

Tng dn vic un nng cho n khi khi trng bay ln v tip tc un nng thm 20 pht. ngui, thmcn thn 300 ml nc, lm ngui v lc trong sut qu trnh thm

Chuyn nh lng dung dch vo bnh nh mc dung tch 500 ml, pha long n vch mc v lc u.- Chng ct: chuyn 50 ml dung dch mu th trn vo bnh chng ct A. Thm khong 300 ml nc,

mt vi git hn hp ch th v vi vin bi thu tinh.

Bi m vo phn ni ca dng c. Lp ng chng ct B vo bnh A v ni vi ng sinh hn D.

Cho 40 ml dung dch axit sunfuric chun 0,5 N, khong 80 ml nc v vi git dung dch ch th hn hpvo bnh E. Ni bnh E vi ng sinh hn D v m rng tt c phn ni u khng b d kh. S dng kp l xoF i vi dng c c ng ni hnh cu.

Dng phu nh git C thm vo bnh A mt lowowngj dung dch natri hidroxit va trung ho v sau thm d 25 ml na ( gi li t nht mt vi ml dung dch trn).

Sau khi s dng dng c nh m t trn, ct vo bnh E mt lng dung dch ct khong 250 n 300ml. Ngng un nng, m nt phu nh git C, tho ng dn B ra v cn thn ra ng sinh hn D, thu nc ravo bnh E. Cui cng tho bnh thu hi E ra.

- Chun b:

Lc cn thn dung dch cha trong bnh thu hi E v trong hai bu qu l bn v chun ngc lngd dung dch axit sunfuric chun vi dungdch natri hidroxit chun 0,5 N cho n lc ch th chuyn mu.

Trong sut qu trnh chun phi cn thn lc bnh m bo rng dung dch hon ton c lc u.

2.3.1.5 Tnh ton kt qu

Hm lng nit ( X1) c tnh bng phn trm khi lng theocng thc:

500 100

X1= ( V1- V2) . 0,007004 . .

50 m

7,004 ( V1 V2)

X1 =

m

trong :V1- th tch dung dch natri hidroxit chun dng chun ngc lng d dung dch axit sunfuric chun

cho vo bnh E th nghim mu trng, tnh bng ml;

V2- th tch dung dch natri hidroxit chun dng chun ngc lng d dung dch axit sunfuric chun cho vo bnh E xc nh, tnh bng ml;

m-khi lng mu th, tnh bng g;

0,007004- khi lng nit ng vi 1ml dung dch axit sunfuric ng 0,5 N, tnh bng.

Ch thch : Nu dng nng ca dung dch natri hidroxit chun khng ng vi qui nh v thuc th,phi tin hnh iu chnh li nng cho thch hp

2.3.2 Phng php th tch s dng focmandehyt

2.3.2.1 Dung dch v thuc th

Axit sunfuric, dung dch 0,5 N

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Focmandehyt, dung dch 25 %

Phenolphtalein, dung idhcj 1 % trong etanol;

Metyl , dung dch 0,1 %.

2.3.2.2 Tin hnh th

Cn 5 g mu vi chnh xc n 0,0001 g, ho tan trong bnh nh mc 250 ml vi mt t nc ct, thmn vch mc, lc u. Dng pipet ly 20 ml cho vo bnh nn dung tch 250 ml, thm 3 ml axit sunfuric , lcu. y bnh bng phu lc ui ngn v t trn bp in c li aming, un cn thn cho n khi bt khCO2ngng bay ra v ng thi xut hin kh lu hunh trioxit bay ra.

yn 5-10 pht, ly bnh ra ngui n nhit phng rri thm 2 -3 git ch th metyl , lc nhbnh,dng natri hidroxit 5 N trung ho cho n khi dung dch chuyn sang mu hng nht. Thm vo 15 -20 ml dungdch focmandehyt trung tnh v 5 git ch th phenolphtalein, lc u v yn 1-2 pht.

Dng natri hidroxit 0,5 N chun cho n khi dung dch c mu hng nht khng bin mt sau 5 pht.

Hm lng nit (X1) qui ra gc kh, tnh bng phn trm khi lng theo cng thc:

V .N . 0,01401 . 250 . k

X 1=

100 - X3

G. 20

100

trong :

V- th tch natri hidroxit 0,5 N tiu hao khi chun ;

k- h s hiu chnh nng ca natri hidroxit theo 0,5 N;

0,01401 -lng nit tng ng vi 1 ml dung dch natri hidroxit 0,5 N

G-lng mu th tnh bng gam;

X3- m ca ur, tnh bng %.

2.4 Xc nh hm lng biuret

2.4.1 Nguyn tc ca phng php

To phc mu tm gia biuret v ng sunfat khi c mt dung dch baz kali-natri tatrat . o mu caphc cht to thnh bc sng 550 nm.

Nu trong phn dung dch ly th c mt lng mui amoni tnh chuyn ra NH3ln hn 15 mg, phi tinhnh loi n trc khi xc nh

2.4.2 Thuc th

- nc ct mi un si v ngui;- ng sunfat, dung dch 15 g/l;

Ho tan 15 g ng ( II) sunfat ngm 5 phn t nc ( CuSO 4. 5H2O) vo nc, pha long ti 1000 ml v lcu.

- kali-natri tactrat, dung dch baz 50g/l: ho tan 50,0 g kali-natri tactrat ngm 4 phn t nc (NaKH4O6. 4H2O) vo nc; thm 40 g natri hidroxit ra s b lp ngoi, pha long ti 1000 ml v lc u.

- axit sunfuric, dung dch 0,1N

- Natri hidroxit, dung dch 0,1N

- Buret, dung dch tiu chun 2,00 g/l:

a) lm sch buret: ra buret bng dung dch amoni hidroxit 100 g/l v bng nc cho n khi ion amoinc kh, loi nc bng cch ra axeton v cui cng sy kh khong 105 0C.

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b) Chun b dung dch tiu chun: cn 1 g biuret c lm sch mc a vi chnh xc 0,001 g. Hotan vo 450 ml nc v iu chnh pH ca dung dung dch n 7 bng cch thm hoc l dung dch axitsunfuric 0,1 N hoc l dung dch natri hidroxit 0,1 N. dng giy ch th kim ta pH. Chuyn ht dungdch vo bnh nh mc dung tch 500 ml, pha long ti vch mc, lc u, 1 ml dung dch tiu chun ny cha2,00 mg biuret.

- giy ch th xanh brmthymol hoc giy ch th c pH trong khong 6-8

2.4.3 Dng c

Cc dng c thng thng trong phng th nghim v- bnh cch thu c iu chnh nhit 25 1 0C

- my so mu n sc hoc my so mu thng

2.4.4 Qa trnh xc nh

2.4.4.1 Mu th: Cn 50 g mu th vi chnh xc 0,01 g

2.4.4.2 Mu trng: lm mt mu trng song song vi mu th, s dng thuc th v th t cho cc thucth nh i vi mu th.

2.4.4.3 Chun b ng cong chun

a) chun b dung dch tiu chun so mu vi cuvet 4 hoc cuvet 5 cm.

Cho vo bnh nh mc dung tch 100 ml mt lng dung dch tiu chun nh cho trong bng 1

bng 1

lng dung dch biuret tiu chun,ml

khi lng biuret tng ng, mg

0*

0,505,0

15,0

25,0

40,0

0

110

30

50

80

Ch thch : 0*dung dch so snh

Thm vo mi bnh trc ht l mt lng nc cn thit c th tch khong 50 ml, thm 20 ml dung dch

kali-natri tactrat v 20 ml dung dch ng sunfat. Pha long ti vch mc v lc u. Nhng vo bnh cch thu c iu chnh nhit 25 10C v gi khong 20 pht v thnh thong li lc u.

b) Tin hnh so mu: Sau khi khng qu 30 pht, tin hnh so mu trn my so mu thng bcsng khong 550 nm hoc trn my so mu n sc vi knh lc thch hp, sau khi iu chnh thit b trnv v tr 0 so vi dung dch so snh.

c) Xy dng th chun

Lp th, t trn trc honh s mg biuret c trong 100 ml dung dch biuret tiu chun, cn t trn trctung gi tr tng ng ca mt quang.

d) tin hnh xc nh

- chun b dung dch th : cho mu th vo cc c dung tch thch hp ( v d 400 ml) v ho tan mutrong khong 100 ml nc. iu chnh pH n 7 bng cch thm hoc l dung dch axit sunfuric 0,1 N hocdung dch natri hidroxit 0,1 N v dng giy ch th kim tra pH. Chuyn nh lng dung dch vo bnhnh mc dung tch 250 ml, pha long n vch mc v lc u.

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- hin m u : ly chnh xc mt lngh dung dch th c cha khong 10 -80 mg biuret vo bnh nhmc dung tch 100 ml. Sau thm vo 20 ml dung dch kali- natri tactrat v 20 ml dung dch ng sunfat, saumi ln thm phi lc u dung dch cha trong bnh. Pha long ti vch mc v lc u. Nhng bnh vo

bnhcch thu c iu chnh nhit 25 1 0C v gi nhit phng trong khong 20 pht.

- So mu : Tin hnh so mu vi mu th v mu trng theo quy trnh mc b sau khi iu chnhthit b o ti im 0 so vi nc.

Ch thch : - nu dung dch b c hay c mu, ly mt lng dung dch thch hp hin mu v thchin qu trnh nh nu trn nhng khng thm ng sunfat. S dng dung dch ny iu chnh thit bo v im 0 v tin hnh so mu dung dch tht

- nu dung dch th b c th trc khi iu chnh pH : thm vo dung dch 2 ml dung dch axitclohidric nng 1 % , lc tht mnh v lc di iu kin p sut thp ( chn khng ) qua phu thu tinh xp (kch thc l gia 5 v 15 m. Ra giy lc v cc bng mt t nc, thu nh lng dung dch lc vo cc vtin hnh iu chnh pH v pha long nh nu trong mc 2 ca phn chun b dung dch th

2.4.5 Tnh ton kt qu

Da vo th chun ( mc c), tm c hm lng biuret tng ng vi gi tr mt quang o c

Hm lng biuret [ ( NH2CO)2NH] ( X2) c tnh bng phn tm khi lng theo cng thc:

( m1 - m2) . D . 100

X2=

m0

trong

D -t s gia th tch dung dch th v th tch dung dch ly xc nh

m0- khi lng mu th, tnh bng g;

m1 - khilng biuret c trong dung dch ly th, tnh bng g;

m2- khi lng biuret tng ng vi lng dung dch ly lm mu trng, tnh bng g.

2.4.6 Trng hp c bit

Khi trong phn dung dch ly th c cha mt lng mui amoni tnh chuyn ra NH3ln hn 15 mg.

Ch thch : C th xc nh hm lng mui bng cch o s bin i gi tr ph vi s c mtfocmandehyt. Nu php o tiu tn ht hn 90 ml dung dch natri hidroxit 0,05 N v lng uree cha trong

phn dung dch ly th ln hn 10 g phi tin hnh xs l theo cc quy nh iu2.4.5

2.4.6.1 Nguyn tc

Loi amoniac bng cch trao i cation trn nha ion.

Xc nh hm lng biuret trong nc gii hp theo phng php nu trn

2.4.6.2 Thuc thTheo iu 2.4.2 v nha trao i cation loi mnh. V d cc loi nha DOWEX 50 v AMBERLITE I-R

120 hoc tng ng l hon ton thch hp vi yu cu trn

2.4.6.3 Dng c

Theo iu 2.4.3 v ct trao i c lp kho pha cui, cao 320 mm, ng knh ngoi 8 mm.

2.4.6.4 Qa trnh xc nh

a) mu th : Cn 20 g mu th chnh xc n 0,01g

b) Mu trng: tin hnh theo mc 2.4.4.2

c) chun b ng cong chun: tin hnh theo mc 2.4.4.3

d) tin hnh xc nh:

-x l nha trao i: ch ho 100 g nha trao i ( 2.4.6.2 ) bng cch gn 4 ln vi axit clohidric 4 N, miln 250 ml v sau ra li vi 1000 ml nc

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- chun b ct trao i: cho lng nha trao i trn vo ct ( 2.4.6.3) n chiu cao 200 mm, ra v npnc vo ct cho n khi mc nc cao hn nha 5 mm.

- chun b dung dch th

cho mu th a) vo cc c dung tch thch hp ( v d 200 ml), ho tan vo khong 50 ml nc.

Cho dung dch chy qua ct chun b mc d) vi tc 150 ml/ h. Thu ly dch gii hp vo bnh nhmc dung tch 250 ml. Dng nc ra nha cho n khi tng th tch thu c khong 220 ml. Kh axit trongdung dch gii hp bng cch them vo dung dch natri hidroxit 0,1 N cho n pH = 7 th theo giy ch th . Pha

long bng nc n vch mc, lc u.- Hin mu: tin hnh theo mc d) ca iu 2.4.4.3 ( phn hin mu)

- So mu: tin hnh theo mc d) ca iu 2.4.4.3 ( phn so mu).

- Tnh ton kt qu: theo iu 2.4 5

2.5 Xc nh m

2.5.1 Dng c v thit b

- t sy, iu chnh c nhit 50 -1100C;

- cn phn tch c chnh xc n 0,0002 g;

- bnh ht m- chn cn.

2.5.2 Tin hnh th

Cn 5 g mu th vi chnh xc n 0,0002 g cho vo chn thu tinh hoc chn s c np c sy nhit 105 110 0 C n khi lng khng i v cn chnh xc n 0,0002 g.

Cho chn c cha mu vo t sy, sy nhit 70 20C n khi lng khng i ( khong 2 gi). ynp chn ly chn ra cho vo bnh ht m, ngui n nhit phng ri em cn vi chnh xc

2.5.3 Tnh kt qu

m ca ure ( X3) c tnh bng phn trm khi lng theo cng thc:

m1m2

X3 = . 100

M

Trong

m1- khi lng ca mu v chn trc khi sy, tnh bng g;

m2- khi lng ca mu v chn sau khi sy, tnh bng g

m- khi lng mu th, tnh bng g.

2.6. Xc nh c ht

Tin hn xc nh theo TCVN 4853 -89 v thm cc quy nh sau:2.6.1 Mu th: ly mu v chun b mu theo phn 1 TCVN 2620-1994

2.6.2 Thit b th

- my sng theo TCVN 4853-89.

- Sng c l vung kch thc l 1,0 mm v 2,5 mm

- Cn k thut sai s khng qu 0,1 g

2.6.3 Tin hnh th

Cn khong 200 g mu vi sai s khng qu 0,1 g v cho vo sng trn my hoc bng tay.Tin hnh sng

trong khong thi gian 30 s trn my hoc cho n khi ht bi nu sng bng tay. Sau khi sng, cn phn mu lt qua sng kch thc l 2,5 mm v cn li trn sng kch thc l 1,0 mm, vi sai s khng qua 0,1 g.

2.6.4 Tnh ton kt qu

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C ht ca ure t 1,0 2.5 mm ( X4) c tnh bng phn trm khi lng theo cng thc:

m1.100

X4=

m

Trong

m- khi lng mu th, g;

m1- khi lng mu th lt qua sng kch thc l 2,5 mm v cn li trn sng kch thc l 1,0 mm2.6.5 Kt qu cui cng ca php th l gi tr trung bnh cng ca hai ln xc nh song song c lch

khng qu 1 % gi tr tuyt i