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t I u c h u n v I t n a m

TCVN 6637 : 2000

ISO 10530 : 1992

cht lng nc - xc nh sunfua ho tan -

Phng php o quang dng metylen xanh

Water quality - Determination of dissolved sulfide -

Photometric method using methylen blue

H ni - 2000

tcvn

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Li ni u

TCVN 6637 : 2000 hon ton tng ng vi ISO 10530 : 1992

TCVN 6637 : 2000 do Ban k thut tiu chun TCVN/TC147

Cht lng nc bin son, Tng cc Tiu chun o lng

Cht lng ngh, B Khoa hc, Cng ngh v Mi trng

ban hnh.

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Cht lng nc Xc nh sunfua ha tan

Phng php o quang dng metylen xanh

Water quality Determination of dissolved sulfide

Photometric method using methylen blue

1 Phm vi p dng

1.1 Khong nng p dng

Tiu chun ny qui nh phng php o quang xc nh sunfua ha tan trong nc. Phng

php ny p dng xc nh sunfua ha tan nng 0,04 mg/l n 1,5 mg/l.

Nhng nng cao hn c th c xc nh bng cch gim lng mu v pha long mu nc.

Phng php ny c p dng cho nc thi, nc t nhin khng yu cu lc.

1.2 Cn tr

Nhng ion sau y khng cn tr vic xc nh nu nng ca chng cha t hoc vt

Xianua 2 mg/l

Iodua 20 mg/l

Thiosunfat 900 mg/l

Thioxianat 900 mg/l

Sunfit 700 mg/l

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Xc nh phn sunfua trong polysunfua bng phng php ny l khng hon ton.

Cacbon disunfua khi nng < 10 mg/l v / hoc etyl mecaptan < 1 mg/l khng nh hng n phng php.

Nc khng lc c theo iu 6 khng th phn tch bng phng php ny. Trong trng hp ny,

sunfua d gii phng pH 4 c th c xc nh (mt tiu chun quc t v vn ny ang c

son tho).

2 Tiu chun trch dn

TCVN 5993:1995 (ISO 5667-3:1985) Cht lng nc - Ly mu - Hng dn bo qun v x l mu.

3 Nguyn tc

Lc mu tch cht rn l lng v sunfua kh tan. Gi sunfua trong nc lc bng cch thm dung

dch ascobic. Gii phng sunfua t nc lc bng nit v chuyn vo bnh hng cha dung dch n c

km axtat.

Thm axit dimetyl-p-phenylendiamin vo bnh hng to leucometylen xanh, ri oxy ha thnh

metylen xanh bng cch thm ion st (III). o hp th ca phc bc sng 665 nm.

4 Thuc th

Ch dng thuc th tinh khit phn tch v nc ct hoc nc c tinh khit tng ng. Nc cn

ui oxy bng bin php thch hp nhun si hoc sc kh nit.

4.1 Axit sunfuric, (H2SO4) = 1,84 g/ml

4.2 Natri hydroxyt (NaOH), dung dch 32 % (m/m), c(NaOH) 10 mol/l.

4.3 Dung dch km axetat

Ha tan 20 g km axetat Zn(CH3COO)22H2O trong nc v pha thnh 1 lt.

Dung dch c th b c nhng iu khng nh hng n vic xc nh.

4.4 Dung dch m phtalat , pH 4,0 + 0,1

Ha tan 80 g kali hydrophtalat (C8H5KO4) trong 920 ml nc. Kim tra pH dung dch v nu cn iu

chnh pH n 4,0 bng dung dch natri hidroxit pha long [c(NaOH) = 1 mol/l] hoc dung dch axit

clohidric [c(HCl) = 1 mol/l].

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4.5 Dung dch atcobic, pH 10 + 0,1

Ha tan 10 g axit atcobic (C6H8O6) trong 90 ml nc v iu chnh n pH 10 bng dung dch NaOH

(4.2). y ngay bnh.

Chun b dung dch ny ngay trc khi dng.

4.6 Dung dch thuc th to mu

Ho 2 g N,N-dimetyl-1,4-phenyl diamoni clorua (C8H14Cl2N2) vo 200 ml nc trong bnh nh mc

1000ml.

Thm cn thn 200 ml axit sunfuric H2SO4 (4.1), lm ngui v thm nc n vch.

4.7 Dung dch amoni st (III) sunfat

Cho 50 g amoni st (III) sunfat (NH4Fe(SO4)212H2O) vo bnh nh mc 500 ml. Thm 10 ml H 2SO

(4.1) v thm nc n vch.

4.8 Dung dch gc natri sunfua

Cho mt lng natri sunfua Na2SxH2O (x = 7 9) tng ng vi 0,5 g sunfua vi hm lng thiosunfa

< 5 % trong bnh nh mc 1000 ml. Thm nc (iu 4) n vch.

Dung dch ny bn 2 n 3 ngy.

Trc khi dng, xc nh nng chnh xc bng phng php iod (xem ph lc A).

4.9 Dung dch chun natri sunfua

Dng pipet ht 10 ml dung dch gc natri sunfua (4.8) cho vo bnh nh mc 1000 ml. Thm nc n vch.

1 ml dung dch tiu chun ny cha khong 5 g sunfua. Nng chnh xc c xc nh bng

phng php iod (xem ph lc A).

Chun b dung dch trc khi dng.

5 Thit b, dng c

5.1 Thit b lc, th d bm tim 3 vng dung tch 50 ml, c mng lc mt chiu (c l 0,45 m) (xem

hnh 1).

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Vi nc kh lc th c th dng thit b lc di p sut bng mng lc (c l 0,45 m) (xem hnh 2).

5.2 Thit b phn gii tch sunfua, th d ch hnh 3, gm bnh phn ng dung tch 250 ml

c c bn ni vi phu nh git dung tch 100 ml, c ng dn kh n tn y bnh phn ng. C

ng sinh hn ng hoc ng ng v bnh hp th.

Kch thc nu hnh 3.

5.3 ng ong, dung tch 25 ml.

5.4 Bnh nh mc, dung tch50 ml, 100 ml, 500 ml v 1000 ml.

5.5 Pipet,dung tch 1 ml v 10 ml.

5.6 Pipet mt vch, dung tch 1 ml, 2 ml, 5 ml, 10 ml, 20 ml, 50 ml v 100 ml.

5.7 My pha ch.

5.8 Bm tim microlit .

5.9 Cp kh nit,tinh khit [99,996 % (m/m)].

5.10 Thit b o tc kh, thch hp o tc 40 l/h.

5.11 pH mt, c in cc thch hp.

5.12 My ph k hoc my quang k dng knh lc, thch hp o hp th bc sng

665 nm.

5.13 Cuvet, 1 cm.

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Knh lc

Hnh 1 Bm tim ba vng.

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Hnh 2 Thit b lc mng

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6 Ly mu v x l trc ti ni ly mu

Nu khng bit trc khong nng ca mu, th cc phn ca mu th c lc v lu gi theo 6.1

v 6.2 cho php xc nh vi lng mu nh hn.

Phn mu lc theo 6.1 v 6.2 cn c phn tch trong vng 24 h.

6.1 Ly mu loi nc d lc

Ht bng pipet 5 ml dung dch ascobic (4.5) vo bnh nh mc 50 ml.

Ht mu nc vo bm tim 3 vng dung tch 50 ml.

Lp ci lc (xem 5.1) v lc nc vo bnh nh mc cho ti khi t vch mc.

6.2 Ly mu loi nc kh lc hn

Ht bng pipet 5 ml dung dch ascobic (4.5) vo bnh nh mc 50 ml.

Thi bnh nh mc v my lc p sut bng nit khong 10 min.

Lc nc cn xc nh vi p sut ni t 2 bar v hng vo bnh nh mc ni trn cho ti vch mc.

Vic ni gia my lc p sut v bnh nh mc cn thit k sao cho tip cn khng kh t nht.

Thi gian lc khng qu 5 min (xem 1.2).

7 Cch tin hnh

7.1 Xc nh

Rt 25 ml dung dch m phlatat (4.4) vo bnh phn ng (xem hnh 3).

Rt 20 ml dung dch km axtat (4.3) vo bnh hp th.

Ni my v cho mt dng nit 40 l/h qua dung dch trong 2 min.

Chuyn mu thu c t iu 6 vo bnh phn ng qua phu nh git.

Trng phu nh git bng lng nh nc (iu 4) v cho mt dng nit 40 l/h qua dung dch trong

30 min.

Tho bnh hp th ra v cho vo 10 ml dung dch thuc th to mu (4.6) v tip theo l 1 ml dung

dch amoni st (III) sunfat (4.7).

Lm y bnh hp th bng nc (iu 4), y kn, lc v i 10 min.

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Chuyn dung dch vo bnh nh mc 100 ml, trng cn thn bnh hp th bng lng nh nc v gp

vo bnh nh mc.

nh mc bng nc (iu 4) v o hp th bc sng 665 nm so vi nc.

Nu nng vt qu 1,5 mg/l sunfua th vic xc nh cn lp li vi lng mu lc nh hn.

7.2 Th trng

Th mu trng nhmu tht ch khc thay mu tht bng nc (iu 4).

hp th ca mu trng khng c lch qu nhiu so vi gi tr tnh ton ASO(xem iu 8).

8 Thit lp ng chun

ng chun thu c khi dng cuvt 1 cm l khng hon ton thng trn ton thang o nng . nh gi ch dng phn thng ca ng chun.

Pha long dung dch tiu chun sunfua (4.9) c cc dung dch hiu chun ph kn thang nng

cn phn tch.

Nng khi lng cc dung dch hiu chun cn tri u trn khong o.

Th d, cho khong nng 0,2 mg/l n 0,7 mg/l (tng ng vi 0,01 n 0,03 mg sunfua) th lm

nhsau:

Ly 20 ml dung dch km axetat (4.3) vo 7 bnh nh mc 100 ml.Dng pipet ht 4 ml, 6 ml, 8 ml, 10 ml, 12 ml v 14 ml dung dch tiu chun sunfua (4.9) cho vo 6

bnh. Bnh th 7 dng cho mu trng.

Thm 10 ml dung dch thuc th to mu (4.6) v 1 ml dung dch amoni st (III) sunfat (4.7) vo m

bnh, thm nc n khong 40 ml.

y cc b nh, lc v nh mc bng nc (iu 4).

Sau 10 n 20 min, o hp th 665 nm, so vi nc trong cuvt i chng.

Nng sunfua trong cc dung dch hiu chun l:

0 (trng); 0,2 mg/l; 0,3 mg/l; 0,4 mg/l; 0,5 mg/l; 0,6 mg/l; 0,7 mg/l.

Xc nh nng chnh xc ca cc dung dch hiu chun bng phng php iod (xem ph lc A).

Trn trc honh t nng khi lng sunfua cc dung dch chun. Trn trc tung t gi tr hp

th tng ng.

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Tnh ng hi qui tuyn tnh.

Bit nng v hp th ca cc dung dch hiu chun c th da vo thng k tnh ton hm chun.

dc b ca ng chun l nhy, tnh bng l/mg. im ng chun ct trc tung l hp th

ASOca mu trng. im ct trc tung v dc cn c kim tra thng xuyn, nht l khi dng l

thuc th mi.Mi my o ph, mi cuvt u c ng chun ring, hm chun ring.

9 Tnh ton

Nng ca sunfua ha tan trong mu nc, tnh bng mg/l, c tnh bng cng thc

trong

Al l hp th ca mu nc (xem 7.1);

Al,0 l hp th ca mu trng (xem 7.2);

l l k hiu ch di quang ca cuvet;

f l h s chuyn, f= 100 ml;

b l nhy thu c theo iu 8, tnh bng lit trn miligam;

V l th tch mu lc dng phn tch, V= 45 ml.

Khi tnh kt qu, mi bc pha long cn tnh n.

10 Biu th kt qu

Nng sunfua ha tan trong mu nc c lm trn n 0,01 mg nhng khng qu 2 s c ngha.

Th d

sunfua ha tan: 0,55 mg/l.

11 c tnh ca phng php

V lc cc mu khng n nh l mt phn ca tiu chun ny, v s vn chuyn mu l kh khn do

tnh khng bn ca sunfua ha tan nn mt nghin cu so snh c tin hnh thay cho php th

bV

A fll )A( 0,

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lin phng th nghim. Nghin cu so snh ny c lm bi cc nh phn tch trong 1 phng th

nghim.

Dung dch sunfua cha 1 mg sunfua trn lt c dng xc nh.

Hm chun c xc nh l

y= 0,010 79 x+ 0,022 8

c tnh ca phng php cho bng 1.

Ch thch 1 - i vi cc thnh vin c bo co hn bn gi tr trng bn gi tr u tin c dng

nh gi.

12 Bo co kt qu

Bo co kt qu cn gm nhng thng tin sau:

a) trch dn tiu chun ny;

b) nhn dng mu;

c) biu th kt qu, ph hp vi mc 10;

d) x l mu trc;

e) mi s lch khi phng php ny hoc mi tnh hung c th gy nh hng n kt qu.

Bng 1 c tnh ca phng php

Thng s l n na

%

x

mg/l

r

mg/l

VC r

%

R

mg/l

VCR

%

Mu 7 28 0,0 1,152 0,020 6 1,8 0,020 9 1,8

l l s thnh vin;

n l s gi tr o;

na phn trm loi b;

x l gi tr trung bnh;

r l lch chun lp li;

VC r l h s lch lp li;

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R l lch chun ti lp;

VCR l h s lch ti lp;

Ph lc A(qui nh)

nh chun dung dch gc sunfua

Dng pipet ht 25 ml dung dch iot (c = 0,05 mol/l) vo bnh nn 250 ml v thm nc n khong

100ml.

Thm 10 ml axit axtic v dng pipet ht 50 ml dung dch gc sunfua (4.8) cho vo dung dch iot.

hn hp phn ng khong 3 pht.

Chun lng diot bng dung dch thiosunfat (c= 0,1 mol/l) n mu vng nht. Thm h tinh bt

v chun tip n khng mu.

Tnh nng dung dch gc sunfua, tnh bng mg/l, bng cng thc sau:

( ) ,V V1 2 1 604 100

50

trong

V1 l th tch dung dch iot, tnh bng mililit;

V2 l th tch dung dch thiosunfat tiu tn, tnh bng mililit;

1,604 l h s hp thc ca phn ng.

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