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

TCVN 6663-14 : 2000

ISO 5667-14 : 1998

cht lng nc ly muphn 14: hng dn m bo cht lng

ly mu v s l mu nc mi trng

Water quality SamplingPart 14: Guidance on quality assurance of environmental water

sampling and handling

H ni - 2000

Li ni u

TCVN 6663-14 : 2000 hon ton tng ng vi

ISO 5667-14 : 1998.

TCVN 6663-14 : 2000 do Ban k thut Tiu chun

TCVN/TC 147 Cht lng nc bin son, Tngcc Tiu chun o lng Cht lng ngh, BKhoa hc Cng ngh v Mi trng ban hnh.

3t i u c h u n v i t n a m TCVN 6663-14 : 2000

Cht lng nc Ly muPhn 14: Hng dn m bo cht lng ly mu v x l mu

nc mi trng

Water quality SamplingPart 14: Guidance on quality assurance of environmental water sampling and handling

Cnh bo: Phi xem xt v gim thiu mi nguy c v tun th cc quy nh v an ton. Xem cc

ch an ton trong ISO 5667-1, bao gm c vic ly mu t thuyn v trn sng.

1 Phm vi p dng

Tiu chun ny a ra hng dn v la chn v s dng cc k thut m bo cht lng khc nhau

lin quan n vic ly mu th cng nc mt, nc ung, nc thi, nc bin v nc ngm.

Ch thch Cc nguyn tc chung nu ra trong tiu chun ny c th p dng cho vic ly mu bn v cnlng trong mt s trng hp.

2 Tiu chun trch dn

ISO 5667-1: 1980, Cht lng nc - Ly mu - Phn 1: Hng dn lp cc chng trnh ly mu

TCVN 5993-1996 (ISO 5667-3: 1985), Cht lng nc - Ly mu - Hng dn bo qun v x l mu.

3 nh ngha

Cc nh ngha sau y c p dng cho tiu chun ny (TCVN 6663-14: 2000 /ISO 5667-14:1998)

3.1 ng

gn nhau v s tng ng gia mt kt qu kim tra v gi tr i chng c chp nhn.

[ISO 3534-1]

TCVN 6663-14 : 2000

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Ch thch Khi nim ng, khi p dng vo mt lot cc kt qu kim tra, bao gm s kt hp ca ccyu t sai s hoc lch ngu nhin v h thng.

3.2 chch

s khc nhau gia k vng ca kt qu kim tra v gi tr i chng c chp nhn.

[ISO 3534-1]

Ch thch lch l sai s ton b mang tnh h thng, ngc li vi sai s ngu nhin. C th c mt hocnhiu thnh phn sai s mang tnh h thng gp phn to ra lch. lch cng ln phn nh s sai khc

h thng cng ln so vi gi tr i chng c chp nhn .

3.3 chnh xc

gn nhau v s tng ng gia cc kt qu c lp thu c trong nhng iu kin quy nh.

[ISO 3534-1]

Ch thch 1 S bin ng i km theo cc kt qu kim tra do cc thao tc ly mu lp s bao gm binng t qu trnh phn tch cng nh cc nguyn nhn t qu trnh ly mu. C th so snh sai s ngu nhin

ca vic ly mu lp vi sai s ngu nhin t phn tch lp trn cng mu suy ra sai s do ly mu so vi

sai s ngu nhin tng.

Ch thch 2 chun xc ch ph thuc vo s phn b cc sai s ngu nhin v khng lin quan n gi trthc hay gi tr l thuyt (ISO 3534-1). Php o chun xc c th hin theo lch chun. chun xc

c ci thin l c th hin khi lch chun c gi tr nh.

Ch thch 3 "Tnh c lp" ca cc kt qu kim tra phn nh gii hn m ti cc kt qu thu c theocch khng b nh hng bi kt qu phn tch mu trc (ISO 3534-1). Cc php o nh lng chun

xc rt ph thuc vo cc iu kin quy nh. Nhng thut ng thng c bit n nh l " lp li" v "

ti lp" lin quan n cc loi iu kin quy nh nht nh. " lp li" tng ng vi cc php o c tin

hnh trong nhng iu kin c kim sot (bi cng mt bin php, c tun th cht ch trong cng mt

phng th nghim); cn " ti lp" cp ti cng mt bin php song c dng trong nhiu phng th nghim

khc nhau.

3.4 tnh i din

l mc trong iu kin ca tt c cc mu nc c ly t thu vc phn nh iu kin ca nc

cn nghin cu

3.5 tng hp

mc tho thun v mt kim sot cc sai s ngu nhin v sai s h thng

TCVN 6663-14 : 2000

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3.6 vt liu i chng c chng nhn (CRM)

vt liu n nh v ng nht, c thnh phn gn khp vi thnh phn ca mu cn phn tch, nng

cc thnh phn cn phn tch trong vt liu c bit vi mt bt nh xc nh.

Ch thch Trong hu ht cc phn tch ha hc, c th c c kh nng truy nguyn ca php o bng mtlot hiu chnh cho thy khng c s mt mt cc thng s cn xc nh hoc s nhim bn trong qu trnh x

l mu. Kh nng truy nguyn ny c th da vo phn tch CRM.

3.7 gi tr mu trng

gi tr quan st thu c khi tin hnh php o trn mt mu ging ht mu cn nghin cu, song khng

cha cht cn xc nh.

Ch thch Cc mu trng ti hin trng l nhng mu trng trong phng th nghim c mang ra hintrng, c x l nh mu tht v c phn tch kim tra quy trnh ly mu.

[ISO/TR 13530]

3.8 gi tr mu thm

lng bit v thnh phn cn xc nh c b sung vo mu, thng l tnh sai s h thng ca

mt h thng phn tch bng phng php pht hin.

[ISO/TR 13530]

3.9 tm thy

l mt lng ti thiu no bit ca mt cht cn phn tch c thm vo mu m c th o c

bng mt h thng phn tch.

Ch thch gi tr pht hin c tnh t s khc nhau gia cc kt qu phn tch ca phn mu c thm vphn mu khng thm v thng c tnh bng phn trm (%).

[ISO/TR 13530]

3.10 biu kim sot

l biu c cc gii hn trn v gii hn di, trong cc gi tr ca mt s php o thng k ca

mt lot mu tht, mu thm v mu trng, c lp thnh biu v thng tng ng vi ngy thng

hoc th t s mu.

Ch thch 1 Biu thng c mt ng trung tm d nhn ra xu th ca cc gi tr c xc nh trnbiu v mt trong hai gii hn kim sot.

[ISO 3534-2]

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Ch thch 2 Trong mt s biu kim sot, cc gii hn kim sot c da trn cc s liu ca ring l lp trn biu ; trong khi vi mt s biu khc th cc gii hn kim sot ny li da vo cc tiu chun

c chp nhn hoc cc gi tr quy nh p dng cho c trng thng k c dng.

Ch thch 3 Biu tng tch ly l mt dng biu kim sot. Dng biu ny dng pht hin nhngthay i nh thng xuyn theo xu th m c th nu dng biu kim sot Shewhart th cha chc pht

hin ra. Nguyn tc c bn ca dng biu tng tch ly ph bin nht l da trn gi tr c lp ln biu

l tng tch ly ca cc lch ca cc thng k mu lin tip so vi mt gi tr ch. Khi c mt thay i no

v qu trnh, tng s tr v khng. To ca mi im c v s l tng i s ca to im trc v

lch hin ti so vi gi tr ch.

Cc biu tng tch ly thng c phn tch qua cc im hng ln trn bng phng php chng,

s xut hin mt du hiu nu ng tng tch lu giao nhau hay chm ng bin ca th (ISO

3534-2).

3.11 biu kim sot Shewhart

l biu kim sot cho thy qu trnh c c kim sot v mt thng k hay khng

[ISO 3534-2 v ISO 8258]

Ch thch c th l mt biu dng cc c trng nh tnh (v d, phn khng ph hp) nh gi mtqu trnh, hoc c th l mt biu dng cc c trng nh lng (v d, s trung bnh v dy) nh gi

mt qu trnh. Mt s v d l:

Biu gi tr trung bnh - cc gi tr trung bnh c v thnh th kim sot gi tr trung bnh ca mtbin s;

Biu gi tr cc dy mu c v thnh th kim sot thay i ca mt bin s; Biu lch chun - cc lch chun ca mu c v thnh th kim sot thay i ca mt

bin s;

Biu bin thin - bin thin ca mu c v thnh th kim sot thay i ca mt bin s; Biu C - s lng cc sai li (theo mi l, tng ngy, tng my, v.v...) c v trn biu .

3.12 gii hn can thip trn [di]

gi tr thng k ang xt no nm gii hn trn [di], hay nm ngoi khi nht thit phi thc hin mt

hnh ng can thip

[ISO 3534-2]

Ch thch Cc gii hn ny da trn gi thit l ch 0,3% cc kt qu phn b bnh thng s nm ngoinhng gii hn ny. iu c ngha chc chn rng nhng nguyn nhn ph hay cha chc chn gy ra thay

i cng vn c th tn ti v c th phi tin hnh xc nh v gim thiu cc nguyn nhn .

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3.13 gii hn cnh bo kim sot trn [di]

gi tr thng k ang xt no vi xc sut cao nm gii hn di [trn] ( gii hn trn hoc di),

hay nm gia khi qu trnh ang c kim sot .

[ISO 3534-2]

Ch thch 1 Khi gi tr thng k c tnh ton t mt mu nm ngoi cc gii hn cnh bo nhng nm tronggii hn can thip, nhn chung cn tng cng gim st qu trnh v c th p dng cc quy tc can thip

trong mt s qu trnh nht nh.

Ch thch 2 Ti cc gii hn cnh bo, cn ch n kh nng c cc iu kin ngoi kim sot, tuy nhinkhng cn c tin hnh thm bin php.

Ch thch 3 Cc gii hn cnh bo lun lun nm trong gii hn can thip .Ch thch 4 Cc gii hn cnh bo thng c xc nh sao cho thng thng ch 5% kt qu nm bnngoi cc gii hn . Trong mt s trng hp nht nh, cc kt qu lin tip nm ngoi gii hn cnh bo

biu th rng cc nguyn nhn gy ra s thay i l hin hu v cn c bin php can thip nhn bit

v gim bt cc sai s.

Ch thch 5 Cc gii hn c tnh t lch chun ca gi tr thng k c xem xt ca t nht l 20 mu.Cc gii hn cnh bo v can thip c p dng cho cc kt qu ly mu ring l.

3.14 ng trung tm

l ng thng trong biu kim sot th hin gi tr trung bnh theo mt thi gian lu di hoc mt gi

tr c xc nh trc ca php o thng k c lp thnh th.

[ISO 3534-2]

4 Ngun sai s ly mu

Cc ngun gy sai s bao gm nhng ngun sau y:

a) Nhim bn

Nhim bn c th do cc vt liu ca thit b ly mu gy ra (bnh ly mu v bnh ng mu), do s

nhim bn ln nhau gia cc mu v do cch bo qun, lu kho khng thch hp v do cc b tr

vn chuyn mu.

b) Tnh khng n nh ca mu

Loi bnh ly mu v bnh ng mu s dng c th nh hng n bn vng ca cht cn xc

nh trong khong thi gian t lc ly mu n lc phn tch do tnh khng bn vng c hu ca

bn thn mu v do cc iu kin trong mu c lu gi v vn chuyn.

c) Bo qun mu khng ph hp

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Vic la chn cc bnh ly mu v bnh ng mu nh hng n s thng nht gia cht cn xc

nh vi cc gii php bo qun c th c, nh c trnh by c th trong TCVN 5993: 1995 (ISO

5667-3).

d) Ly mu khng ng

Ly mu sai khc vi quy trnh ly mu, hoc bn thn quy trnh ly mu sai c th l mt ngun gy

sai s.

e) Ly mu t nhng thu vc khng ng nht.

f) Vn chuyn mu (xem iu 6)

5 Cc k thut kim sot cht lng qu trnh ly mu

5.1 Khi qut

TCVN 5992: 1995 (ISO 5667-2) nh ngha ly mu l qu trnh ly mt phn c coi l i din ca

mt vng nc (hoc bn hoc cn lng), nhm kim tra cc c tnh khc nhau c qui nh ca

nc.

Hng dn v quy trnh kim sot cht lng di y c th c dng nhn dng v nh lng cc

sai s lin quan n vic ly mu.

Ti liu ny khng nhm xem xt ton b vic m bo cht lng p dng cho ly mu. Tuy nhin,

phi nhn mnh rng cc bin php kim sot cht lng cp di y s phi c p dng nghim

tc nht trong bi cnh kim sot cht lng c t chc tt. iu ny bao gm c vic xem xt ton

b phng php ly mu xem c thch hp vi mc ch d nh khng. Trong , cn cn nhc vic la

chn cc k thut ly mu, v tr ly mu, s lng v loi mu phi ly, o to nhn vin ly mu, vn

chuyn mu, bo qun v lu gi mu. Phng php la chn phi c vit thnh ti liu y v

phi lp mt h thng lu gi v ghi chp ti liu. Mt chng trnh kim sot cht lng thch hp c th

gm mt hoc tt c cc k thut lit k di y. Vic kim sot cht lng ly mu ph thuc vo mc

tiu ca chng trnh, song t nht 2 % cng sc phn tch nn dnh cho vic qun l cht lng ly

mu.

Nh cp trc y, cc bin php kim sot cht lng ly mu c ba mc tiu chnh sau y:

a) Cung cp c phng thc gim st v pht hin cc sai s ly mu v do l mt bin php

loi cc d liu khng hp l hoc sai lc;

b) Chng minh c rng cc sai s ly mu c kim sot mt cch thch hp; v

c) Ch ra c s bin ng ca vic ly mu v t truy nguyn c kha cnh rt quan trng

ca sai s.

Cc k thut kim sot cht lng c miu t di y l:

ly cc mu lp kim tra chnh xc ca qu trnh ly mu;

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s dng cc mu trng ti hin trng gim st cc ngun gy nhim bn mu; s dng cc mu thm khi kim sot cht lng nh gi n nh ca mu trong qu trnhvn chuyn v lu mu.

5.2 Cc mu lp kim sot cht lng

Mc ny c th dng cho hng lot phng php kim sot cht lng nhm nh gi sai s ngu nhin

lin quan vi cc mc khc nhau n qu trnh ly mu :

a) bin ng do phn tch: lp li cc php phn tch i vi cng mt mu trong phng th nghim

nh gi sai s phn tch nht thi

b) bin ng do phn tch + ly mu con/vn chuyn mu: phn tch cc mu lp ly ti hin trng

(B1 v B2) t mu chung (B) (mu ly c bng cch p dng mt ln quy trnh ly mu). S khc

nhau gia cc s liu nh vy s cho c c lng v s bin ng do phn tch cng vi s bin

ng do ly mu (gm c vic lu mu nhng khng tnh n cc nh hng t bnh ly mu).

c) thay i do phn tch + do ly mu tng : phn tch cc mu t mu chung thu c bng cch p

dng ring r quy trnh ly mu. Cch ny ch ra s thay i ca ton b qu trnh ly mu v phn

tch (A1 v A2).

Mi lin h gia cc bin ng ly mu khc nhau trong v d b) v c) c minh ho di dng gin

trong hnh 1.

Hnh 1 - Mi lin h gia cc bin ng khc nhau do ly mu

Btng mu n

B1 B2

Chia lm 2 mu con

A1 A2

2 mu n

a1 a2 b11 b12 b21 b22

im ly mu

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S khc nhau gia A1 v A2 cho php c lng cc bin ng trong qu trnh ly mu (ly mu, bnh

cha, lu mu v phn tch).

S khc nhau gia B1 v B2 (c th hin di dng gi tr trung bnh ca b11 & b12, v b21 & b22) cho

php c lng cc bin ng do phn tch v bin ng trong qu trnh ly mu (gm vic lu mu

nhng khng tnh n thay i do bnh ng mu).

S khc nhau gia cc phn tch lp b11 & b12, v b21 & b22 cho php c lng tp trung ca kt qu

phn tch.

Vic phn tch cc mu lp cho php c lng c s gp phn ca sai s phn tch i vi tt c

cc v d trong hnh 2 n hnh 7.

So snh gia cc c lng khc nhau v bin ng m t trn c th dng phn nh nhng

ngun quan trng nht to ra bt nh ca php o. iu ny c minh ha trong bng 1 v bng 2

di y.

Bng 1 - bin ng phn tch

Mu s 1 2 3 4 5 6 7

Kt qu lp - 1

- 2

1,61

1,55

1,72

1,98

2,21

1,99

1,38

1,55

2,25

2,44

2,8

2,55

1,74

1,55

c lng ca

bin ng (1 bc t

do)

0,001 8 0,033 8 0,024 2 0,014 45 0,018 05 0,031 25 0,018 05

Ch thch c lng ca bin ng (gi tr trung bnh ca cc lch nu trn) vi 7 bc t do =0,020 23.

Cc kt qu lp sau y c c t mt lot mu nc thi, mi mu c chia lm hai phn mu

phn tch. Cc mu ny c phn tch v cho nhng kt qu di y.

Bng 2 - bin ng phn tch + ly mu con/vn chuyn mu

Mu s 1 2 3 4 5 6

Kt qu lp - 1

- 2

2,66

1,85

1,66

2,22

2,31

1,44

1,99

1,55

1,85

2,54

1,81

2,65

c lng bin

ng (1 bc t do)

0,328 1 0,156 8 0,378 5 0,096 8 0,238 1 0,352 8

Ch thch 1: c lng bin ng phn tch v bin ng x l mu - vi 6 bc t do = 0,258.

Ch thch 2: Nng mu c chn phi tng t nh nng c chn trong bng 1.

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Hai gi tr c lng v bin ng do phn tch v bin ng do phn tch + ly mu con/vn chuyn

mu c th c so snh nh p dng mt cch thch hp php kim tra F (F-test) : gi tr F thu c =

12,75.

Gi tr F t cc bng ny (vi 7 v 6 bc t do v mc xc sut l 95%) = 4,2.

Gi tr F quan st c ln hn cc gi tr bng 1 v bng 2 - do c l do tin rng c nhng

ngun gy bin ng quan trng giai on ly mu/x l mu. Trong trng hp cc mu c ly, v

d xc nh amoniac, c th xem xt kh nng phi lu n vic bo qun mu hoc kh nng

nng b thay i trong giai on ly mu.

5.3 Cc mu trng ti hin trng

K thut ny c th dng phn nh cc sai s lin quan n vic nhim bn bnh cha mu v qu

trnh ly mu (xem hnh 2).

Trong phng th nghim, chia mu nc loi ion ra lm hai phn, Phn A v Phn B. Gi phn A li

trong phng th nghim. Mang Phn B ra hin trng v chia lm hai phn mu nh b1 v b2.

Phn mu b1 phi c x l dng bnh ly mu v k thut cng ging nh mu tht cng tt.

Phn mu b2 phi c gi li v a tr li phng th nghim m khng tin hnh bt c x l no ti

hin trng.

Phn mu b1 c x l nh mt mu tht, cng vi phn mu b2 khng c s dng, c a v

phng th nghim phn tch.

(X l nh mu tht) (Khng s dng)

Hnh 2 - Cc mu trng ti hin trng dng nc loi ion

So snh kt qu ca Phn A v phn mu b1 xc nh ra sai s do ly mu, x l v vn chuyn mu.

Nc loi ion

Phn A(Gi li trong phng th nghim)

Chuyn ra hin trng

Phn B(Chia nh)

Phn mu b1 Phn mu b2

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So snh kt qu ca phn A v phn mu b2 xc nh ra sai s do vic vn chuyn mu.

So snh kt qu ca phn mu b1 v phn mu b2 xc nh ra sai s do nhim bn bnh ly mu hoc

qu trnh ly mu.

5.4 Ra thit b (cc bnh ly mu)

K thut ny c th dng phn nh cc sai s lin quan n vic nhim bn cc thit b ly mu v

qu trnh ly mu do khng xc ra sch cc bnh ly mu (xem hnh 3).

Cc quy trnh lin quan n cc mu trng ti hin trng c th c s dng ti ch ngay sau giai

on ly mu.

Trong phng th nghim, chia mt mu nc loi ion thnh hai phn, Phn A v Phn B. Gi Phn A

li trong phng th nghim. Mang Phn B ra hin trng v chia lm hai phn mu nh b1 v b2.

Phn mu b1 s phi c x l cho vic ra bnh ly mu vi k thut cng ging vi cc mu tht cng

tt.

Phn mu b2 c gi li v a tr li phng th nghim m khng c mt x l no ti hin trng.

Phn mu b1, cng vi phn mu b2 khng c s dng, c a v phng th nghim phn tch.

So snh kt qu ca Phn A v phn mu b1 xc nh ra sai s do vic cha lm sch k cc bnh ly

mu.

So snh kt qu ca phn A v phn mu b2 xc nh ra sai s do vic vn chuyn mu.

So snh kt qu ca phn mu b1 v phn mu b2, xc nh ra sai s do nhim bn bnh ly mu hoc

qu trnh ly mu v cha lm sch k cc bnh ly mu.

Hnh 3 - Ra thit b bng mu trng (nc loi ion)

5.5 Hiu sut lc

Nc loi ion

Chuyn ra hin trng

Phn A(Gi li trong phng th nghim)

Phn B(Chia nh)

Phn b1(Ra thit b v x l nh mu tht)

Phn b2(Khng s dng)

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5.5.1 Khi qut

K thut ny dng xc nh sai s lin quan n vic nhim bn bnh ly mu v qu trnh ly mu c

lin quan n vic lc.

Khi c yu cu lc mu ti hin trng, th cc mu trng hin trng v/hoc cc mu dng m

bo cht lng theo tiu chun u phi c x l bng vic s dng cc quy trnh lc ging nh dng

cho mu tht.

5.5.2 Lc mu trng (nc loi ion)

K thut ny dng phn nh bt k sai s no lin quan n bnh ly mu, thit b lc, qu trnh ly

mu v vic nhim bn mu (xem hnh 4).

Trong phng th nghim, chia mt mu nc loi ion ra lm hai phn, Phn A v Phn B. Gi phn A

li trong phng th nghim. Mang Phn B ra hin trng v chia lm hai phn mu nh b1 v b2.

X l phn mu b1 dng bnh ly mu v thit b lc v cng mt k thut cng ging vi vi cc mu

tht cng tt.

Phn mu b2 c gi li v a tr li phng th nghim, khng c mt x l no ti hin trng.

Phn mu b1 c x l nh mu tht, cng vi phn mu b2 khng c s dng, c a v phng

th nghim phn tch.

Hnh 4 - Lc mu trng (nc loi ion)

So snh kt qu ca Phn A v phn mu b1 xc nh ra sai s do lc khi ly mu, do x l mu khi ly

mu v vn chuyn mu.

So snh kt qu ca phn A v phn mu b2 xc nh ra sai s do vic vn chuyn mu.

So snh kt qu ca phn mu b1 v phn mu b2 xc nh ra sai s do nhim bn bnh ly mu hoc

cc qu trnh ly mu trong khi lc

Nc loi ion

Chuyn ra hin trng

Phn A(Gi li trong phng th nghim)

Phn B(Chia nh)

Phn b1(Lc v x l nh mu tht)

Phn b2(Khng s dng)

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5.5.3 Lc mu m bo cht lng bng phng php thm

Phng php ny c th dng xc nh ra cc sai s lin quan n bnh ly mu, thit b lc, cc qu

trnh ly mu, v tnh khng n nh ca mu v nhim bn mu (xem hnh 5).

Trong phng th nghim, chun b mt mu mi trng c phn tch trc bng cch thm vo

mu mt lng bit ca cht cn xc nh. Lng cht cn xc nh thm vo phi c chn sao

cho cc php o c tin hnh i vi nng c th thu c chnh xc tt nht.

Chia mu ra lm hai phn, Phn A v Phn B. Phn A c gi li trong phng th nghim. Phn B c

mang ra hin trng v chia ra thnh hai phn b1 v b2.

Phn mu b1 s c x l vi vic dng bnh ly mu v thit b lc cng nh k thut cng ging vi

mu tht cng tt.

Phn mu b2 c gi li v a tr li phng th nghim, khng c bt c x l no ti hin trng.

Phn mu b1 c x l nh mu tht, cng vi phn mu b2 khng c s dng, c a v phng

th nghim phn tch.

Hnh 5 - Lc mu thm m bo cht lng

So snh kt qu ca Phn A v phn mu b1 xc nh ra sai s do ly mu, bao gm cc qu trnh ly

mu, thit b lc, khng n nh mu v vn chuyn mu

So snh kt qu ca phn A v phn mu b2 xc nh ra sai s do vic vn chuyn mu.

So snh kt qu ca phn mu b1 v phn mu b2 xc nh ra sai s do nhim bn cc bnh ly mu,

thit b lc v cc qu trnh ly mu, v cc sai s do mu khng bn vng v mu b nhim bn.

5.6 Cc mu thm

5.6.1 Khi qut

mu thm

Chuyn ra hin trng

Phn A(Gi li trong phng th nghim)

Phn B(Chia nh tip)

Phn b1(Lc v x l nh mu tht)

Phn b2(Khng s dng)

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K thut ny dng nh gi sai s h thng ca qu trnh ly mu, bao gm vic xc nh cc sai s

lin quan n bnh ly mu b nhim bn v qu trnh ly mu. K thut ny c bit c gi tr trong vic

xc nh cc sai s do mu khng n nh, bao gm vic hao ht cc cht cn xc nh do bay hi, hp

th hoc cc yu t sinh hc; v d, cc cht cn xc nh nh cc hp cht hu c d bay hi, kim loi

vt (khi lc mu) v cc cht dinh dng. C hai k thut chnh, l thm mu vo nc loi ion

(xem hnh 6) v thm vo mu mi trng (xem hnh 7).

5.6.2 Cc mu thm vo nc loi ion

Trong phng th nghim, chia mt mu thm t nc loi ion thnh hai phn, Phn A v Phn B.

Phn A c gi li trong phng th nghim. Phn B c mang ra hin trng v chia nh thnh ba

phn b1 b2,, v b3.

Phn mu b1 c x l, dng bnh ly mu cng ging nh i vi cc mu tht cng nhiu cng tt.

Phn mu b2 c gi li v a tr li phng th nghim, khng c bt c mt x l thm no ti hin

trng.

Phn mu b3 s phi c thm vi nng bit ca cht cn xc nh v sau c chia nh lm

hai phn b3 (i) v b3(ii).

Phn mu b3 (i) s c x l dng cng bnh ly mu v cng mt k thut cng ging cc mu tht

cng tt

Phn mu b3(ii) c gi li v mang tr li phng th nghim, khng c thm bt c x l no ti hin

trng.

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Hnh 6 - Mu nc loi ion c thm

Hnh 7 - Mu mi trng c thm

Mu mi trng c thm

Phn A(Gi li trong phng th nghim)

Chuyn ra hin trng

Nc loi ion

Phn B(Chia nh)

Chuyn ra hin trng

Phn b1(X l nh mu tht)

Phn A(Gi li trong phng th nghim)

Phn b2(Khng s dng)

Phn B(Chia nh)

Phn b1(X l nh mu tht)

Phn b3(c thm vo)

Phn b2(Khng s dng)

Phn b3(i)Bnh cha mu (nh mu tht)

Phn b3(ii)(khng s dng)

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Chuyn cc phn mu b1, b2, b3(i) v b3(ii) tr li phng th nghim phn tch.

So snh kt qu ca Phn A v phn mu b1 xc nh sai s do qu trnh x l khi ly mu v vn

chuyn.

So snh kt qu ca Phn A v phn mu b2 xc nh ra sai s do vic vn chuyn mu.

So snh kt qu ca Phn A v phn mu thm vo b3(ii) xc nh ra cc sai s do bt k mt s

khng n nh no ca mu, b nhim bn v vn chuyn mu.

So snh kt qu ca Phn A v phn mu thm vo b3(i) xc nh ra sai s do x l mu v vn chuyn,

v cc sai s do bt k mt s khng n nh, b nhim bn no ca mu.

So snh kt qu ca phn mu b1 v phn mu b2 xc nh ra sai s do nhim bn bnh ly mu v

x l khi ly mu (loi tr cc sai s do vn chuyn).

So snh kt qu ca phn mu b2 v b3(ii) xc nh ra sai s do mu khng n nh v b nhim bn.

So snh kt qu ca phn mu b3(i) v b3(ii) xc nh ra sai s do s nhim bn cc bnh ly mu

hoc do cc qu trnh ly mu.

5.6.3 Mu mi trng c thm

L tng nht l mu nn c thm hin trng ti thi im ly mu. Vic ny c th cn chuyn gia

c chuyn mn v c th khng thng dng i vi phn tch thng nht.

C th chun b ti phng th nghim mt mu mi trng c phn tch t trc bng cch thm

cht cn xc nh vo mu. Lng cht cn xc nh b sung ny phi c chn sao cho php phn

tch c tin hnh nng m ti thu c chnh xc cao nht.

Chia mu ny thnh hai phn, Phn A v Phn B. Gi phn A li trong phng th nghim. Mang Phn B

ra hin trng v li c chia lm hai phn mu nh b1 v b2.

Phi x l phn mu b1 dng bnh ly mu v k thut cng ging vi cc mu tht cng tt

Phn b2 c gi li v a tr li phng th nghim, khng c thm bt k mt x l no ti hin trng.

Phn mu b1 c x l nh mu tht, cng vi phn mu b2 khng s dng, c a v phng th

nghim phn tch.

So snh kt qu ca Phn A v phn mu b1 xc nh ra sai s do x l mu v vn chuyn.

So snh kt qu ca phn A v phn mu b2 xc nh ra sai s do vic vn chuyn mu.

So snh kt qu ca phn mu b1 v phn mu b2 xc nh ra sai s do nhim bn bnh ly mu v qu

trnh ly mu v cc sai s do mu khng n nh v b nhim bn.

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6 Vn chuyn, n nh v lu mu

Cn tham kho TCVN 5993: 1995 (ISO 5667-3) xem hng dn v cch x l v bo qun mu. iu

c bn l phi cn thn m bo tt c cc cht bo qun c chun b v pha ch chnh xc.

o v ghi li ngay ti ch nhit mu . Cc thng s vt l (v d nh pH, kh ha tan, cht rn l

lng) phi c xc nh ti ch hoc ngay sau khi ly mu cng sm cng tt.

Cn m bo cc bnh ng mu phi c a ti phng th nghim ging nh cc mu thng nht.

Nn y kn bnh ng mu v trnh b nh hng ca nh sng v nhit cao qu, v cc tnh cht ca

mu c th nhanh chng b bin i do trao i kh, cc phn ng ha hc v s trao i cht ca cc

sinh vt c th c mt trong mu. Cn m bo nhng mu khng th phn tch ngay th c n nh

ngay. C th lm lnh mu xung 4 oC; v bo qun trong thi gian di hn, lm lnh xung n

- 20 oC nh hng dn trong TCVN 5993: 1995 (ISO 5667-3). Trong trng hp ny, phi m bo mu

tan hon ton trc khi s dng, v qu trnh ng lnh c th gy ra s tp trung ca mt s thnh phn

phn trong ca mu, l phn ng bng sau cng. Cc mu c th c bo qun bng cch thm

ha cht vo vi nhng lng thch hp. Cn chn bin php bo qun khng lm nh hng n vic

phn tch tip theo hoc nh hng n cc kt qu. Ghi li tt c cc bc bo qun trong bo co th

nghim.

Ch thch Cc mu m bo cht lng trong vn chuyn, n nh v lu gi phi c x l bng ccqu trnh y ht nh i vi mu th nghim.

7 Phn tch v gii trnh cc s liu kim sot cht lng

Mc ch ca h thng kim sot cht lng l m bo rng tin cy ca cc s liu ly mu l

nht qun vi cc tiu ch tin hnh yu cu.

7.1 Biu kim sot Shewhart

Biu Shewhart l loi biu c s dng rng ri nht (xem ISO 8258). y l dng biu m

trn bin s cn quan tm c v lin tip nhau. Cc gi tr o c s c so snh vi gi tr kim

sot. Ch cn kim tra trc tip trn biu l c th thu c nhiu thng tin (xem hnh A.1 v A.2)

7.2 Lp biu kim sot khi ch c hai kt qu th lp

Biu ny c dng mt th, trn sai lch gia hai php xc nh lp, d, c lp thnh biu .

d = R1- R2

trong :

R1 l kt qu phn tch ca mu u tin

R2 l kt qu phn tch ca mu th hai

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iu c bn l phi lun lun ly kt qu ca ln phn tch th nht tr i kt qu ln th hai v v ra

trn biu vi lu n du ca n. Gi tr mong i i vi biu ny phi l 0. lch chun ca

mu tng ng, sd, c tnh theo cng thc:

( )s

dmi

m

di D= =

2

1 1

trong

D l sai lch trung bnh gia cc mu lp trn m l mu, v

di l cc sai lch ring l

Ph lc A a ra th d v mt biu kim sot i vi s liu lp v tm thy.

8 Nhn bit mu v ghi chp

Miu t tng im ly mu. Trong trng hp c chng trnh di hn, khng cn nhc li cc iu kin

c tho thun v khng thay i. Trong trng hp ny, ch cn trnh by cc php o ti ch (in

situ) v cc bin s v d nh iu kin thi tit v cn ghi li nhng quan st khng bnh thng.

Khi ly mu, v nhng l do c bit, cn cung cp cc thng tin chi tit, k c l do ly mu v cc bc

bo qun tin hnh.

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Ph lc A

(tham kho)

Biu kim sot

A.1 Th d v biu kim sot vi s liu lp (hnh A.1)

Hnh A.1 - Biu Shewhart i vi mu kim sot lp

Cc cht rn l lng c xc nh trong mt lot nc thi cng nghip gim st tun th vi tiu

chun thi gii hn l 30mg/l.

Cc v d nu trong hnh A.1, l mt lot cc mu lp c ly ca nc thi c nng cht rn l lng

trong khong c quan tm: 20mg/l n 40mg/l. Gi thit l lch chun ca ly mu v phn tch l

khng i trong ton b gii hp ny. iu ny cho php c lng c tp trung ca qu trnh ly

mu v kim tra c n trn c s phn tch thng nht.

Vi mi trng hp, mt mu nc thi tng c ly v ng nht cn thn. Sau mu tng ny c

chia thnh cc mu con, p dng quy trnh ly mu to ra cc mu th nghim lp. Mi mu th

nghim ny c phn tch mt ln.

Bng A.1 trnh by cc s liu phn tch ca 20 mu lp.

Km theo l biu kim sot tng ng. Gi tr trung tm ca biu c c nh ti gi tr trung bnh

vi sai gia cc s liu lp. Gii hn kim sot can thip v gii hn cnh bo c v tun t lch

chun 3 v 2.

Gii hn can thip

Gii hn cnh bo

Gii hn cnh bo

Gii hn can thip

S mu kim sot

Sailchktqu

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Bng A.1 - S liu v cht rn l lng ca cc mu lp kim sot cht lng

Gi tr o c

mg/l

sai lch

mg/l

Ln th nht Ln th hai

33,2 36,0 - 2,8

25,6 26,2 - 0,6

38,2 34,8 3,4

28,8 27,2 1,6

31,4 29,8 1,6

34,6 32,2 2,4

22,4 24,6 - 2,2

27,2 26,8 0,4

22,0 23,2 - 1,2

34,0 32,8 1,2

24,6 22,6 2,0

23,8 23,0 0,8

33,6 35,2 - 1,6

37,4 36,6 0,8

29,2 31,4 - 2,2

30,0 31,2 - 1,2

36,4 35,8 0,6

37,2 39,4 - 2,2

33,6 35 - 1,4

28,0 26,4 1,6

Vi sai trung bnh 1,0

lch chun ca sai lch 0,471 8

Ch thch: lch chun quan st c th hin chnh xc kt qu phn tch cng nh v ly mu

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A.2 Th d v biu kim sot i vi tm thy (hnh A.2)

Cc s liu di y (xem bng A.2) lin quan n vic xc nh nng vt ca thu ngn trong nc

sng. Vi mi l phn tch, mt php th nghim tm thy i vi mu thm c tin hnh bng cch

phn tch mt mu nc sng trc v sau khi thm vo mt lng 90 ng/l. Cc chi tit ca qu trnh

thm nh sau:

C = Nng ca dng dch thm = 100 g/lV = Th tch lng mu ly = 1 998,2 ml

W = Th tch lng thm vo = 1,8 ml

S = Nng o c trong mu c thm (xem phn di)

U = Nng o c trong mu khng c thm (xem phn di)

Phn trm tm thy c tnh nh sau:

% Tm thy = 100. [S. (V + W) - U . V]/C . W

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Bng A.2 - S liu t th nghim tm thy i vi mu thm

L mu, s

Nng khng

c thm , U

ng/l

Nng c

thm, S

ng/l

tm thy

%

1 14 90 84,5

2 15 100 94,5

3 25 115 100

4 8 103 105,6

5 15 104 98,9

6 3 88 94,4

7 8 95 96,7

8 25 108 92,2

9 13 92 87,8

10 19 104 94,5

11 7 94 96,7

12 28 108 88,9

13 9 98 98,9

14 8 87 98,9

15 33 120 96,7

16 2 84 91,1

17 1 84 92,2

18 8 88 88,9

19 14 89 83,3

20 34 120 95,3

21 12 91 87,8

tm thy trung bnh (%) 93,2

lch chun ca tm thy (%) 5,55

Biu kim sot tm thy (xem hnh A.2) c lp bng gi tr trung bnh hoc c lng ban u

ca lch chun.

Ch thch Khng nn p dng mong i tm thy 100% nu nh tm thy quan st c c v b lch.Gii php tt nht l dng biu da trn tm thy trung bnh ca khong 20 kt qu ban u hay c

lng nh vy. Sau khi lm xong vic quan trng l sot xt xem c s thay i no trong tm thy tht da

theo mc tiu phn tch v lp li biu cho ph hp.

Ch thch lch chun c lng = 5,5 (dng lp biu ) lch chun tnh c = 5,55 (t t nht 20 kt qu).

116

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Ch thch lch chun c lng = 5,5 (dng lp biu ) lch chun tnh c = 5,55 t t nht 20 kt qu.

Hnh A.2 - Biu kim sot Shewhart i vi tm thy

Gii hn cnh bo

Gii hn can thip

Trung bnh tm thy

Gii hn cnh bo

Gii hn can thip

Dytmthy

S mu

72

83

94

105

5 10 15 20

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Ph lc B

(tham kho)

Ti liu tham kho

[1] ISO 3534-1:1993, Thng k - Thut ng v K hiu - Phn 1: Xc sut v cc thut ng thng k

chung

Statistics Vocabulary and symbols Part 1: Probability and general statistical terms.[2] ISO 3534-2:1993, Thng k - Thut ng v K hiu - Phn 1: Kim sot cht lng bng thng k.

Statistics Vocabulary and symbols Part 2: Statistical quality control.[3] TCVN 5992:1995(ISO 5667-2:1991), Cht lng nc - Ly mu - Hng dn k thut ly mu

Water quality Sampling Part 2: Guidance on sampling techniques.[4] ISO 8258:1991, Biu kim sot Shewhart

Shewhart control charts.

[5] ISO/TR 13530:1997, Hng dn chung v kim sot cht lng phn tch i vi phn tch nc

General guidance to analytical quality control for water analysis.

[6] Gardner, M. J., Wilson, A. L. v Cheesman, R. J. (1989) Hng dn v kim sot cht lng phn

tch i vi cng nghip nc, NS30, WRc, Medmenham, Anh quc

A manual on analytical Quality Control for Water Industry, NS30, (1999). WRc, Medmenham, UK.

______________________________

Cht lng nc \( Ly muPhn 14: Hng dn m bo cht lng ly