Cu Fe & Ni in Oils & Fats by Graphite Furnace AAS

8/13/2019 Cu Fe & Ni in Oils & Fats by Graphite Furnace AAS

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Pure Appl. Chem. Vol. 60,No. 6, p . 893-900, 1988.Printed in Great B ritain.@ 1988 IUPAC

INTERNATIONAL UNION OF PUREAND APPLIED CHEMISTRYAPPLIED CHEMISTRY DIVISIONCOMMISSION ON OILS, FATS AND DERIVATIVES

DETERMINATION OF COPPER, IRON ANDNICKEL IN OILS AND FATS BY DIRECTGRAPHITE FURNACE ATOMICABSORPTION SPECTROMETRYResults of a collaborative studyand the standardised method

Prepared for publication byP. W . HEND RIKSE , F. J. SLIKKERVEER , J. ZAALB ERG and A. HAUTFENNE

Unilever Research Laboratory Vlaardingen, The NetherlandsUniversitC Catholique de Louvain, UnitC des ProcCdCs (PR CD ), B-1348 Louvain- la-Neuve,Belgium* Me mb ership of th e Comm ission during the period of the collaborative study (1983-87) wasas follows:Chairman: 1983-85 M. Naudet (France); 1985-87 0 Levin (Sweden); Vice-Chairman: A .Hautfenne (Belgium); Secretary: W. D. Pocklington (UK); Titular Members: J. L. Beare-Rogers (Canada; 1985-87); 8 Kurucz (Hungary; 1985-87); 0 Levin (Sweden; 1983-85); J.Po ko rn j (Czechoslovakia; 1983-85); H . Wessels (FR G) ; Associate Members: J . L. Beare-Rogers (C ana da; 1983-85); A . Dieffenbacher (Switzerland); E . Fedeli (Italy); J. Gracian-Tous (Spain; 1983-85); T . Hashimoto (Jap an; 1985-87); G . Holmer (De nm ark; 1985-87);B.Jacobsberg (Belgium); A . Karleskind (Fran ce; 1985-87); F. H. Koelman (Netherlands); 8Kurucz (Hungary; 1983-85); R. G . Manning (US A); A. T. Moller (De nm ark; 1983-85); R.Ohlson (Sweden; 1985-87); M. Teupel (FRG); A. Visapaa (Finland); G. Zwerenz (Austria);National Representatives: A. M. Gad (Arab Republic of Egypt); N. G. Bazan (Argentina;1983-85); R. R. Brenner (Argentina: 1985-87); A. R. Johnson (Australia); R. C. A Lago(Brazil; 1983-85); D . G. Chobano v (Bulgaria); A . P. Tulloch (Ca nad a); J. Pokornf(Czechoslovakia; 1985-87); G. H olm er (Den ma rk; 1983-85); J. V . Holm (D enm ark; 1985-87); G. Ostermann (FR G); R . Linko (Finland); J. P. Wolff (Fran ce); V. M . Kapoulas(Greece; 1983-85); D. Boskou (Greece; 1985-87); M. Jerfinek (Hungary; 1985-87); N. V .Bringi (Ind ia; 1983-85); A . G . Mathew (India; 1985-87); M . McC arthy (Irelan d; 1983-85);A. M. Sharkey (Ireland; 1985-87); A. Dolev (Israel); E. Tiscornia (Italy); T. Hashimoto(Ja pa n; 1983-85); S. Watanabe (Japan; 1985-87); A. S. H . Ong (Malaysia); P. W . Hendrikse(Netherlands); F. B. Shorland (New Zealand; 1983-85); L. Eyres (New Zealand; 1985-87);W. Zwierzykowski (Poland); G. D . C arr (Republic of South Africa); R . Stoica (Rom ania);M. Gassiot Matas (Spain); R. Ohlson (Sweden; 1983-85); H. Briischweiler (Switzerland); R.Perin (Turkey; 1983-85); T. Tuglular (Turkey; 1985-87); V. L. Rou baijlo (USS R); A . E.Waltking (USA ).

eceased 1987Republication of this report is permitted without the need for formal IUPAC permission on condition that anacknowledgement, with full reference together with IUPAC copyright symbol 0988 IUPAC , is printed.Publication of a translation into another language is subject to the additional condition of prior approval from therelevant IU PA C National Adhering Organization.


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Determ inat ion of copper , i ron and n ickel in o i ls andfats by d i rec t graph i te furnace atom ic absorpt ionspect rometry : resul ts of a col laborat ive s tudy andth e s tandard ised m ethodAbs t r ac t - A descri pt i on i s gi ven of t he devel opment by col l aborat i ve st udy of ast andardi zed method f or t he determ nat i on of copper, i r on and ni ckel i n edi bl e oi l sand f ats by di r ect gr aphi t e f ur nace atom c absor pt i on spect ometr y. The pr ocedur e i sbot h r api d and sensi t i ve al l owi ng det er m nat i on at l evel s of 0 . 0 0 5 - 0 . 2 0 mg/ kg f orcopper and 0.01-1.00mg/ kg f or i r on and ni ckel .I N T R O D U C T I O N

The pro- oxi dant ef f ect of smal l amount s of metal s i n edi bl e oi l s and f ats has been knownf or many year s 1). I n par t i cul ar copper, i r on and ni ckel have a cat al yt i c ef f ect on t hemechani sm of aut oxi dati on 2 - 8 ) . The met al s present i n oi l s and f ats may be of natur al ori gi nor due t o pr ocessi ng acti ons such as bl eachi ng ( Fe), hardeni ng ( Ni , Cu) and cor r osi on ofpr ocessi ng equi pment ( Fe, N ). I n t he oi l s and f at i ndust r y a r api d, accur ate andst andardi zed method f or t he deter m nati on of t hese metal s i s ver y i mport ant f or qual i t ycont r ol .At om c absor pt i on spect omet r y ( AAS) has been general l y accept ed f or t he deter m nati on ofCu, Fe and Ni i n oi l s and f at s, and a vari ety of pr ocedur es based on AAS ar e cur r ent l y used.COLLABORATI VE STUDY

The met hod subj ect ed t o col l abor at i ve st udy was based on a t hor oughl y t est ed procedure.I n order to check the val i di t y of t he method as an i nt ernat i onal st andard method f or bothI UPAC and I SO, t he method has been subj ected to an ext ensi ve i nt ernat i onal col l aborat i vest udy by t he I UPAC Comm ss i on VI3, member s of I SO/ TC34/ SC11 and ot her l abor at or i es wor l dwi de.The met hod st udi ed t ook i nt o account t hat vari ous t ypes of equi pment f or gr aphi t e f ur naceat om c absorpti on spect omet r y can be used. To t hi s end the possi bi l i t y of di l ut i on of t he oi lor f at pr i or to i nj ect i on i nt o the gr aphi t e cel l was gi ven as an al t er nat i ve pr ocedur e.Mat er i al s pr ovi ded f or t he st udy wer e oi l s ( soya bean and gr oundnut ) and f at s ( cocoabut t er s) cont ai ni ng copper, i r on and ni ckel at t hr ee concent r ati on l evel s ( hi gh, medi um andl ow). Ni ckel was not r equi r ed t o be deter m ned i n t he cocoa but t ers si nce t hi s metal i s notnormal l y f ound i n cocoa but t er .Each concent r at i on l evel was r epr esent ed by t wo bat ches. I n t he case of oi l s by soya beanand gr oundnut oi l , and i n the case of f at s by t wo cocoabutt er s. Each sampl e was provi ded i ndupl i cat e ( bl i nd coded) so t hat par t i c i pant s recei ved i n al l 2 4 sampl es. Par t i ci pant s wereasked t o anal yse each sampl e i n dupl i cate and to r eport both val ues obt ai ned. A st ati st i caleval uat i on of t he dat a was made f or each l evel and f or each t ype of sampl e separ at el y.

R E S U L T SDat a scr eeni ng. Fr om 32 l abor at or i es dat a have been r ecei ved f or eval uat i on. Of t hesel aborator i es t hr ee di d not r epor t r esul t s f or Ni and two di d not r eport dupl i cat e r esul t s. Ata f i r st sur vey f our l aborator i es have been excl uded f r om t he t est because of devi at i ons fr omt he met hod. Mor eover , t he Cu dat a f r omone l aborator y wer e j udged unsui t abl e f or i ncl usi on i n

t he t est . The dat a f r omt he remai ni ng l abor at or i es 2 7 f or Cu, 28 f or F e, 27 f or Ni ) havebeen subj ect ed t o t est s f or out l i ers accor di ng to Cochr an and Di xon.Cochr an t est s. As t he 2 4 sampl es anal ysed wer e i n f act 1 2 pai r s of cor r espondi ng sampl es,t he di f f erences bet ween t hese bl i nd ( hi dden) dupl i cates have been t est ed f or st r aggl ers andout l i er s accor di ng to Cochr an s pr ocedur e.Di xon t es t s . Af t er el i m nat i on of t he s i gni f i cant out l i er s ( i . e. s i gni f i cant at t he 1%l evel ) accor di ng t o Cochr an s t est , t he t wel ve batch aver ages per l aborat ory have been t est edf or st r aggl er s and out l i er s accor di ng t o Di xon s pr ocedur e.

many devi at i ons t hat i t has been deci ded to om t t he data f or t hese l aborator i es f r omf ur t hereval uati on. Al l other data have been mai nt ai ned i n t he eval uati on af t er di scardi ng t heout l i ers . Hence, f or t he f i nal cal cul at i ons of r epeat abi l i t y and repr oduc i bi l i t y , t herer emai ns a t otal of 2 5 , 2 8 and 27 l abor at or i es f or copper, i r on and ni ckel dat a respect i vel y.

Most of t he devi at i ons concer ned t he copper data i n whi ch t wo l abor at or i es di spl ayed so

PrecisionI n Tabl e 1 t he batch averages f or Cu, Fe and Ni at each concent r ati on l evel i n l i qui doi l or i n sol i d f at have been l i st ed. The resul t s of t wo batches at one concent r ati on l evelare cl ose enough to each ot her t o be consi der ed r epr esent at i ve of t he same concent r at i on,except f or i r on at t he l ow concent r ati on l evel i n sol i d f at : batch CB1 i s cl oser to themedi um t han t o t he l ow l evel . Ther ef or e, aver ages per concent r ati on l evel have beencal cul at ed i n al l cases except f or t he l ow i r on l evel i n sol i d f a t ; i n t he l at t er case, thecal cul at i on of t he pr eci si on parameter s, t oo, has been carr i ed out per bat ch i nst ead of perconcent rat i on l evel .

894


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Determination of Cu Fe and Ni in oils and fats b y GF S 895

Tabl e 1 Concent r at i on l evel s and average recover i es ( mg/ kg) of Cu, Fe and Ni i n oi l s and fatsConcen- Copper (k 25) Iron (k = 28) Nickel (k 27)trationSubstrate level Batch

Batch Level Batch Level Batch Levelaverages averages averages averages averages averages

High SB 0.1515 0.6764 0.60370.7664GN 0.1344 0.6202 0.7483 0.7291.1429

Oil Medium SB 0.0896 0.4312 0.5067

Fat0,9665

Medium CB1 0.1003 0.59420.1526CB2 0,1554

0.5574 0.5756.1023CB2 0.1042Low CB1 0.0363 0.4137

b b

0.1334.0404CB2 0.0446 a. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Key: SB soya beanotes: a Batch averages are so far apart that they cannot reasonably beregarded as batches from the same concentration level.

Nickel usually does not occur in cocoa butters; measuring wastherefore considered irrelevant.GN groundnutCB = cocoa butter

Tabl e 2 Pr eci si on parameter s (mg/ kg) of t he col l abor at i ve AAS st udy 1984Par eters

r R CV,?A ' CVra SRetal Substrate Concentration mHigh 0.143 0.0055 0.0107 0.030 7.5 0.0214 0.061 15.0

cu O i l Medium 0.065 0,0041 0.0078 0.022 9.2 0.0135 0.036 15.8(k 25) Low 0.036 0.0026 0.0054 0.015 15.1 0.0076 0.021 21.4

High 0.153 0.0073 0.0097 0.027 6.4 0.0270 0.076 17.7Fat Medium 0.102 0.0039 0 . 0 0 5 3 0.016 5.4 0.0192 0.054 16.8

Low 0.040 0.0030 0.0045 0.013 11.2 0.0079 0.022 19.5High 0.746 0.0276 0.0465 0.132 6.2 0.1471 0.416 19.7

Fe Oil Medium 0.469 0.0253 0.0435 0.123 9.3 0.0887 0.251 18.9(k - 28) Low 0.146 0.0174 0.0307 0.087 20 8 0.0397 0.112 26.9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

0.0669 0.169 7.40.0507 0.143 8.60,0395 0.112 9.50.0179 0.051 13.40.0493 0.139 6.40.0475 0.134 9.70.0256 0.073 16.8

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

0.18340.11840.09350.03630.12990.08630.0337

0.519 20.40.355 20.60.264 22.60.103 27.20.367 16.90.244 17.60.095 22.0

.- -- -- - -- - - --

Notes: a. expressed in 2 Key: m -m e an value of the relevant characteristics at the specifiedstandard deviation from known duplicates (analytical error).concentration level.b' as the m-values of both batches

were too far apart, precisionparameters have been given foreach batch separately.

s Asr repeatability standard deviation.r repeatability.CV, repeatability coefficient of variation.sr = reproducibility standard deviation.R reproducibility.CVR reproducibility coefficient of variation.


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896 COMMISSION ON OILS, FATS A ND DERIVATIVES

20

1 5 -

10

5 ;

When t he val ues f or g ( r epeat abi l i t y) and ( reproduci bi l i t y) , as gi ven i n Tabl e 2 , areexpr essed as f unct i ons of t hei r corr espondi ng mean concent r ati on val ues (m, t he f ol l owi ngequati ons ar e obt ai ned:Cu i n oi l r - 0. 0102 + 0. 140 m R 0. 0085 + 0. 358 m [ Eq. l a]i n f at r 0. 0076 0.109 m R 0. 0028 0. 492 m [ Eq. l b]Fe i n oi l r 0. 077 0. 081m R - 0. 040 0. 480 m [ Eq. 2a]i n f at r 0. 026 0. 196 m R - 0. 031 0. 543 m [ Eq. 2b]Ni i n oi l r - 0. 056 0. 127 m R - 0. 027 0. 442 m [ Eq. 31

30 0 - i r on,A ni c kel ,copper;n oi l ,- - - i n f at .

(A) : r epeat abi l i t y;B): reproduc i bi l i t y .

-

1 5 - .\.L , , L , C 8 3 1 I < I l l U l

D I S C U S S I O NDuplicates

Two t ypes of dupl i cates have t o be di st i ngui shed:- dupl i cate deter m nati ons i n t he same sampl e, so t he oper at or knows t he concent r at i ons to- dupl i cate sampl es of whi ch t he i dent i t y has been hi dden by r andom zati on and codi ng.be f ound shoul d be equal ;

Two t ypes of st andar d devi at i ons have t heref ore been der i ved:- SA, t he st andar d devi at i on f r om t he known dupl i cat es, al so i ndi cat ed as anal yt i cal err or;- s r , t he r epeatabi l i t y st andar d devi at i on, whi ch i s one of t he parameters asked f or i ncol l abor at i ve st udi es .

From Tabl e 2 i t i s cl ear t hat sr der i ved f r ombl i nd dupl i cat es i s gener al l y consi derabl yl ar ger t han SA; t hi s means t hat t he repeat abi l i t y, est i mat ed f r om uni f or ml evelcol l abor at i ve st udi es as i ndi cat ed by I S0 (9) wi l l of t en be an underest i mate of t he tr uer epeat abi l i t y . The i ncor por at i on of bl i nd dupl i cat es ( doubl e spl i t l evel ) i s t her ef or epref er r ed.Relat ive precisio n

Fr om t he equati ons descr i bi ng t he pr eci si on as l i near f unct i ons of t he met alconcent r at i on ( Eqs. 1- 3) i t can be concl uded t hat t he st r ai ght l i nes corr espondi ng to t heseequat i ons do not pass t hr ough the or i gi n, but i nt er sect t he or di nat e i nvar i abl y at posi t i veval ues . Thi s i mpl i es t hat t he rel at i ve pr ec i s i on ( t he coef f i c i ent s of var i at i on) wi l l tend t obe i nver sel y pr oport i onal t o t he metal concent r ati on measured ( Tabl e 2). When t hesecoef f i c i ent s of var i at i on ar e pl ot t ed agai nst t he met al concent r at i ons on a l og- scal edabsc i ssa ( F i g. l ) , i t can be s een t hat bot h f or r epeat abi l i t y and repr oduci bi l i t y t hecoeff i ci ent s of vari at i on i ncrease appr oxi matel y l i near l y wi t h decr easi ng l ogar i t hms of met alconcent r at i on. Thi s f i ndi ng i s i n agr eement wi t h t hat publ i shed r ecent l y by Hor wi t z 10).Accor di ng to t he l at t er paper, f or an anal yti cal method t o be accept abl e, t he rel ati ver epr oduci bi l i t y shoul d be about 16% at t he 1 mg/ kg l evel , 23% at t he 0. 1mg/ kg l evel , and 3 2at t he 0. 01mg/ kg l evel . For ni ckel t hi s cr i t er i on i s compl i ed wi t h, f or copper t he pr eci s i oni s even ( much) bet t er, whereas f or i r on i t i s not f ul l y met , t he pr eci si on bei ng about 20 att he 1 mg/ kg l evel and bet ween 35 and 40% at t he 0. 1mg/ kg l evel .

C O N C L U S I O NDi r ect gr aphi t e f ur nace atom c absorpt i on spect r ometr y i s a r api d and sensi t i ve methodwhi ch al l ows r el i abl e det er m nat i on of t he tot al concent r at i on of copper, i r on and ni ckel i nedi bl e oi l s and f at s .

and many ot her s f ound t he met hod accept abl e as an anal yt i cal met hod f or t he det er m nat i on oft race concent r ati ons of t hese met al s i n edi bl e oi l s and f at s.t he st andardi sed pr ocedur e i s gi ven on t he f ol l owi ng pages.

Af t er an ext ensi ve col l abor at i ve st udy, par t i ci pant s f r omt he Comm ssi on, I SO/ TC34/ SCl 1On t he basi s of t he r esul t s t he Comm si on has deci ded t o adopt t he met hod. The t ext of


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Determination o f Cu, Fe and Ni in oils and fats y GF S 897

2 631 DETERMINATION OF COPPER IRON AND NICKEL BYDIRECT GRAPHITE FURNACE A TOM IC A BSO RPTIONSPECTROMETRY1 S C O P E A N D F IE L D OF A P P L I C A T I O N

Thi s St andar d descr i bes a met hod f or t he det er m nat i on of t r ace amount s ( pg/ kg) of copper ,i r on and ni ckel i n a l l t ypes of crude or r ef i ned oi l s and f at s, i nc l udi ng cont am nant s f rombl eachi ng ear t h and/ or cat al ysts.

2 . P R I N C I P L EVapor i sat i on of t he oi l / f at i n a sui t abl e gr aphi t e f ur nace connected t o an atom c absorpti onspect r ometer , pr evi ousl y cal i br ated usi ng st andard sol ut i ons of organocompounds of copper ,i r on and ni ckel . Measurement of t he metal cont ent f r om t he obser ved absorpt i ons at sel ect edwavel engt hs. The el ement s ar e anal ysed sequenti al l y.

3 . A P P A R A T U S3 . 1 Pol yet hyl ene or pol ypr opyl ene- cappedbot t l es , 20 and 50 m , met al - f r ee ( Note 1).3 . 2 M cropi pet to r s - 20 and 50 p l3 . 3 Pi pet t or t i ps .3.4 At om c absorpt i on spect r ometer . - Equi pped wi t h ei t her peak hei ght mode and pr i nt er ,or cont i nuous mode and pen r ecorder ( f ul l scal e response i n 0.2 s ) t ogether wi t happropri at e hol l ow cat hode t ubes and deut eri umbackgr ound cor r ect or. The spect r ometershoul d be l ocat ed i n a dust - f r ee atmosphere.3 . 5 Gr aphi t e f ur nace at om ser ( equi pped wi t h f aci l i t i es) .3.6 Gr aphi t e tubes f or use i n a f ur nace atom ser 3.5).3.7 Chr omat ogr aphi c col umns ( di amet er/ hei ght r at i o 1/10) ( Not e 2).3.8 El ectr i c oven - Regul at ed at 60 f 2 C and sui t abl e f or heat i ng at 1 5 0 C .3 . 9 Water bat h.

4 R E A G E N T S4. 1n- Hept ane, anal yt i cal gr ade.4.2 L i ght pet r ol eum b . p. 4O- 6O0C, anal yt i cal gr ade.4.3 Sunf l ower o i l , r ef i ned, or a s i m l ar , s t abl e l i qui d oi l wi t h a l ow met al cont ent (Note4.4 Al um ni um oxi de, chr omatogr aphi c gr ade ( Note 3 ) .4.5 Ni t r i c ac i d, 2M, f ree f r om t races of i r on, ni ckel and copper .4.6 Ni obi um ni t rate N b N O 3 ) 5 ) , aqueous sol ut i on 1000 mg/ l ( Not e 4).4.7 St andard st ock sol ut i ons - St ock sol ut i ons of Fe 10 mg/ kg, Ni 10 mg/ kg and Cu 2 mg/ kg,

2 ) .

pr epar ed by appr opr i ate di l ut i on of or ganomet al l i c s t andar ds wi t h sunf l ower oi l 4.3)( Not e 5 ) .t he stock sol ut i ons 4.7)wi t h l ow met al cont ent 4.3):4.8 St andard worki ng sol ut i ons. - Pr epar e dai l y t he f ol l owi ng worki ng sol ut i ons by di l ut i ng

Copper 0. 05, 0. 1, 0. 2 mg/ kgI r on 0.25, 0. 5, 1. 0mg/ kgNi ckel 0.25, 0.5, 1. 0mg/ kg4.9 Ar gon, pur i t y 99.99 m ni mum ( Not e 6).

5 . P R O C E D U R E5. 1 Treatment of sampl es and sol ut i ons

Pl ace al l sampl es and worki ng sol ut i ons i n t he oven 3 . 8 ) dur i ng t he peri od ofdet erm nat i on.Shake sampl es vi gorousl y bef ore anal ysi s.I f t he met al cont ent of a crude oi l i s known t o be out si de the range speci f i ed f or t hest andards i n 4.8), i l ut e t he sampl e wi t h l ow- met al cont ent oi l 4.3) o br i ng t he met alcont ent wi t hi n t hat r ange.5. 2 Pr epar at i on of appar at us

Swi t ch on t he atom c absorpt i on spect r ometer 3.4) and t he D 2 cor r ect or. I n accor dancewi t h t he i nst r uct i ons of t he manuf actur er, adj ust : l amp cur r ent , s l i t , wavel engt h andampl i f i cati on. The r equi r ed wavel engt hs are (nm:Copper 324.7I r o n 302.1Ni ckel 232.0


6/8

898 COMMISSION ON OILS, FATS AN D DERIVATIVES

Opt i m ze the posi t i on of t he gr aphi t e f ur nace atom ser 3 . 5 ) i n t he at om c absorpti onspect r omet er 3 . 4 ) and set t he requi r ed pr ogr amme f or t he f urnace as f ol l ows:Step Temp, Rampt i me Hol dt i me I nt . gas f l ow( C) S) ( s ) ( m / m n )

For Cu 1 900 5 0 3 0 3 0 02 2 7 0 0 1 5 5 0

For Fe , Ni 1 1 2 0 0 5 0 30 3 0 02 2 7 0 0 1 5 5 0I f i t i s not possi bl e t o pr ogr amme t he gr aphi t e f ur nace exactl y as above, use acompar at i ve progr amme s ui t abl e f or t he equi pment ( Not e 7).Use a nor mal graphi t e t ube ( Not e 8).Pr et r eat t he pi pet t or t i p 3 . 3 ) by pi pet t i ng (usi ng a m cropi pet t or , 3 . 2 ) and thendi scar di ng 20 p hept ane. The f i l m of hept ane remai ni ng on t he wal l of t he t i pf aci l i t at es a r epr oduci bl e t r ansf er of t he oi l sampl e. The t i p has t o be pr et r eat edbef or e each i nj ect i on of an oi l sampl e.

5 . 3 Determ nati on5. 3. 1 Gr aphi t e t ube bl ank.Record t he absor pt i on, i f any, of t he gr aphi t e tube 3 . 6 ) as such and autozero t hi sabsor pt i on,5. 3. 2L i qui d oi l bl ank .By means of a m cr opi pet t or ( 3 . 2 ) , i nj ec t 20 p l ow- met al oi l 4 . 3 ) i nt o the gr aphi t ef ur nace 3 . 5 ) , i ni t i at e t he t emper at ure pr ogr amme and r ecor d t he absor pti on.

By means of a m cr opi pet t or 3 . 3 ) , i nj ect 20 p of t he t hr ee st andard worki ng sol ut i onsof t he met al under i nvest i gati on 4 . 8 ) i nt o t he gr aphi t e f ur nace 3 . 5 ) and recor d t heabsor pt i on.5 . 3 . 3 St andardi sati on of appar at us.

5 . 3 . 4 Sampl e f or anal ysi s.5 . 3 . 4 . 1 Oi l ( l i qui d) sampl es .

By means of a m cr opi pet t or 3 . 2 ) , i nj ect 2 0 p of t he oi l sampl e i nt o the gr aphi t ef ur nace 3 . 5 ) , i ni t i at e t he t emper at ur e programme and recor d t he absor pt i on.5 . 3 . 4 . 2 Fat sampl es ( m p. 4 0 C and hi gher ) .By means of a m cr opi pet t or 3 . 2 ) , i nt r oduce an ext r a t emper at ure pr ogr amm ng st ep:hol dt i me 20 s - t emperat ur e 60C - i nt er nal gas f l ow 0 m / m n. I ni t i at e t het emper at ure progr amme. W t hi n t he f i r st progr amme st ep i nt r oduce by means of am cropi pet t or 3 . 2 ) , 2 0 p 1 of t he mel t ed f at i nt o t he gr aphi t e f ur nace (3. 5) , al l owt he t i p to r emai n i n t he i nj ect i on openi ng to l i quefy t he f at and t hen i nj ect . Recor dt he absor pt i on (Note 9).

Car r y out t wo det erm nat i ons i n r api d successi on.5. 3. 5 Number of det er m nat i ons.

6 EXPRE SSI ON OF RESULTS6. 1 Cal cul at i on

Measur e t he peak hei ght on t he recor der chart or r ead f r om t he di spl ay or pr i nt er.Dr aw a cal i br ati on cur ve by pl ott i ng t he absor pt i on of t he thr ee st andards 5 . 3 . 3 ) ,cor r ect ed f or t he bl ank 5 . 3 . 2 ) , agai nst t hei r r espect i ve metal cont ent s ( Note 10).Read the metal cont ent of t he sampl e f r omt he r el evant cal i br ati on cur ve.Repor t as t he f i nal r esul t t he mean of t he resul t s of t he two det er m nati ons, pr ovi dedt he requi r ement s f or r epeat abi l i t y 6 . 2 ) ar e met . I f t he r equi r ement s f or r epeat abi l i t yar e not met , di scar d t he resul t s and carr y out a f ur t her t wo det er m nati ons on the t estsampl e.

6 . 2 Repeat abi l i t y val ueThe di f f er ences bet ween t he val ues obt ai ned f r om t wo si ngl e det erm nat i ons, car r i ed outi n r api d successi on by t he same oper at or , usi ng t he same apparat us f or t he anal ysi s oft he same t est sampl e, shoul d not be great er t han t he r epeat abi l i t y val ue ( r ) ascal cul ated f r omt he f ormul ae i n Tabl e 1, whi ch expr ess the pr eci si on i n r el at i on to t hedet er m ned mean val ue.


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Determination of Cu Fe and Ni in oi ls and fats b y GFAAS 899

Tabl e 1 Repeat abi l i t y (r) and r epr oduci bi l i t y val ues (R)Metal Subst r ate r R

Oi l 0. 0102 + 0.140m 0. 0085 0. 358 mcu Fat 0. 0076 + 0. 109 m 0. 0028 0. 492 mOi l 0. 077 + 0.081m 0 . 0 4 0 0. 480 mFat 0. 026 0. 196 m 0. 031 0. 543 me

Ni Oi l 0 . 0 5 6 0. 127 m 0. 027 0. 442 mKey: m - cor r espondi ng mean concent r ati on val ue.

6. 3 Repr oduci bi l i t y val ueThe di f f er ence bet ween t he val ues f or t he f i nal r esul t , obt ai ned by t wo ( or mor e)l aborator i es usi ng t hi s s t andar d method f or t he anal ysi s of t he same l aborat ory sampl e,shoul d not be gr eat er t han t he r epr oduci bi l i t y val ue (R) as cal cul at ed f r om t he f or mul aei n Tabl e 1 whi ch expr ess t he pr eci si on i n rel ati on to t he det er m ned mean val ue.

7 N O T E S1. The pol yet hyl ene or pol ypr opyl ene- capped bot t l es are made met al - f r ee i n the f ol l owi ngway :Cl ean the bot t l es t hor oughl y wi t h war m ni t r i c aci d ( 4. 5), r i nse wi t h di st i l l ed wat er and

dr y t he bot t l es i n a dr yi ng oven ( 3. 8) at about 80C.2. A sampl e of a l ow- met al cont ent oi l i s obt ai ned by t he f ol l owi ng pr ocedur e:Di ssol ve 1 par t of oi l (4. 3) (m i n 3 part s (V) of l i ght pet r ol eum (4. 2). Prepar e anal um ni umoxi de col umn ( 3. 7) usi ng tw ce t he mass of al um ni um oxi de 4. 4) , ct i vat ed byheat i ng i n a oven ( 3. 8) at 150C f or 14 h, as t he mass of t he oi l t o be puri f i ed. Add t heoi l sol ut i on t o t he col umn and el ut e wi t h 5 par t s (V) of l i ght pet r ol eum Evapor at e thel i ght petr ol eum of t he el uat e on a heat ed wat er bat h ( 3. 9) usi ng a gent l e st r eamofni t r ogen ( 2- 5 l / mn) (4. 9). Remove f i nal t races of l i ght pet r ol eumunder vacuum3. Merck pr oduct no 1077 i s sui t abl e4 Sol ut i on ( code 88083) i s avai l abl e f r omAl f a Di vi si on, 152 Andover St r eet , Danver s, MA01923, USA.5 . Sui t abl e st andards ar e avai l abl e f r ome. g. Cont i nent al Oi l Company, Ponca Ci t y, Okl ahoma,USA ( Conost an, 5000 mg/ kg) or Mer ck, D - 6100 Dar mst adt , Federal Republ i c of Germany( met al i n standard oi l , 1000 mg/kg) .6. I f ar gon i s not avai l abl e, ni t r ogen may be used as pur ge gas. At t emperat ures above2300C ni t r ogen f or ms t oxi c cyanogen gas; t her ef or e cont i nuous vent i l at i on i n the f ur nacearea shoul d be pr ovi ded.7. I f i n thi s case the backgr ound cor r ect i on f ai l s, di l ut e bl ank, st andar ds and sampl es w t han organi c f at sol vent , e. g. hept ane ( 4. 1) t o a maxi mum of 1: 2 (mm and wor k at ambi entt emperat ure.8. The gr aphi t e t ube f or t he determ nat i on of i r on has t o be coat ed wi t h ni obi um to ensur e

t hat t he tot al amount of i r on i s determ ned. W t h an uncoated t ube the r esul t wi l l var yaccordi ng to t he t ype of i r on compound present i n t he oi l . A sui t abl e coat i ng pr ocedur ei s :By means of a m cr opi pet t or ( 3. 2) , i nj ect 100 p 1 ni obi umni t r at e sol ut i on (4. 6) i nto thef ur nace. Star t t he temperat ure pr ogr amme to dry at l OOC f or 60 s and t hen at om se at2700C f or 5 s . Repeat t hi s pr ocedure unti l 300 p1 of ni obi umni t r at e sol ut i on has beeni nj ec ted. At om se at 2700C t i l l const ant absorbance ( t o remove any i r oncont am nat i on) .


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900 COMMISSION ON OILS, FATS AND DERIVATIVES9. The normal , m ni mum l i m t of detecti on can be i mpr oved by ei t her a gr eat er scal eexpansi on or by r epeat ed i nj ecti ons of t he sampl e at t he end of t he ashi ng operat i ont hen al l owi ng t he progr amme t o pr oceed t o compl et i on. I f t he metal cont ent i s t oo hi gh( i . e. exceeds t he cal i br at i on curve) measur e t he absor pt i on af t er a f ur t her di l ut i on oft he sampl e wi t h sunf l ower oi l .10. W t h t he use of sophi st i cat ed equi pment aut o- cal i br at i on can be appl i ed.

AcknowledgementThe comm ssi on i s t hankful to t he col l abor at ors i n Aust r al i a, Aust r i a, Bel gi um Bul gar i a,Denmar k, Fi nl and, Fr ance, Feder al Republ i c of Ger many, Hungar y, The Net her l ands, Republ i c ofSout h Af r i ca, Sweden, Turkey, Uni t ed Ki ngdomand t he Uni t ed St ates of Amer i ca f or t hei rpar t i c i pat i on and val uabl e cooper at i on.

12.3 .4 .5 .6 .7 .8 .9 .

10.

REFERENCESA. E. Ki ng, H. L. Roschen and W M. I r wi n, Oi l Soap ( Chi cago) , 1933 10, 204.R. Marcuse and P. O. Fredr i kson, J Am. Oi l Chem SOC. , 1971 8 448.0 Not evar p and M. H. Chani ne, J . Am Oi l Chem SOC. , 1972 9 247.W G. Mer t ens, C. F. Swi ndel l s and B. F. Teasdal e, J . Am Oi l Chem SOC. , 1971 8 544.G. R. L i st , C. D. Evans and W F. Kwol ek, J . Am. Oi l Chem SOC. , 1971 8 438G. R. L i st , C. D. Evans, L . T. Bl ack and T. L. Mount s, J Am Oi l , 1978 Chem SOC. 55 275.G. R. L i s t , T. L . Mounts and A. J . Heak i n, J . Am Oi l . Chem S O C . 1978 55 280.G. R. L i st , C. D. Evans and H. A. Moser , J Am Oi l Chem S O C . 1977 9 287.I nt ernat i onal St andar i zat i on Or gani sat i on, IS0 5725-1981.W Horwi t z , Anal . Chem , 1982 5 67A.

Cu Fe & Ni in Oils & Fats by Graphite Furnace AAS

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