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S P E C T R O C H I M I C AA C T APART B

E L S E V I E R Spectrochimica Acta Pa rt B 51 (1 996 ) 211-220

A n e w s o l i d - l i q u i d e x t r a c t i o n s a m p l i n g t e c h n i q u e f o r d i r e c tde termi nat i on o f t race e l ements i n b i o l og i ca l mater i a l s by graphi te

furnace a tomi c absorpt i on spec trometryH i r o t s u g u M i n a m i * , T o m o m i H o n j y o , I k u o A t s u y a

Department of Material Science, Kitami Institute of Technology, 165 Koen-cho, Kitami, Hokkaido 090, JapanReceived 12 January 1995; accepted 11 Apr il 1995

A b s t r a c tA ne w s o l i d - l i qu i d e x t r a c t i on s a mpl i ng t e c hn i que w i t h g r a ph i t e f u r na c e a t omi c a bs o r p t i on s pe c t r ome t r y i s ba s e d onthe quant i t a t ive ex t rac t ion of the e l emen t of in te res t f rom the b io logica l pow dered sam ples in to a l iquid phase of

1 mo l 1 t n i t r ic ac id so lu t ion . E xam ina t ions of the condi t ions for s amp le prepara t ion us ing s ol id- l iqu id ex t rac t ion ( i .e .the e f fec t of conc ent ra t ion o f n i t r ic ac id , s ample m ass and u l t rasonica t ion t ime o n the ext rac t ion) have be en ca r r i edou t i n o r de r to ob t a in 100% e x t r a c ti on o f c a dm i um, c oppe r , l e a d a nd m a nga ne s e f r om pow de r e d b i o l og i c a l s a mp l e sto the l iquid phase . 100% o f ext rac t ion of these m eta l s i s success fu l ly ca r r i ed ou t us ing 1 mo l 1 j n i t ri c ac id , ands e pa r at ion o f s o l i d pha s e a nd l i qu i d pha s e i s done by u s i ng a c e n t r i f uge ( 20 mi n , 4000 r e v mi n -~ ). T he p r opo s e d m e t hodi s appl i ed to the d e te rmina t ion of ca dm ium and l ead a t 0 .1 p~g g-1 leve l s and of co ppe r and ma ngan ese a t 10 tLg g-~l e ve ls i n pow de r e d b i o l og i c a l s a mp l e s . T he s e a na l y ti c a l re s u lt s a r e a s c e r ta i ne d by m i c r ow a ve i nduc e d n i t r oge n p l a s m a -ma s s s pe c t r ome t r y .Detec t ion l imi t s for cadm ium , copper , l ead and ma ngan ese a re , respec t ive ly , 0 .012 ~g g ~, 0 .829 t~g g ~, 0 .082 t~g gand 0 .12 5 p~g g-J in so l id sam ples , w hen 50 mg of pow dered b io logica l s amp les i s ext rac ted in 5 ml o f 1 tool 1 ~ n i tr i cac id and then 10 ILl of ext rac ted so lu t ion i s measured . P rec i s ions of the de te rmina t ion ( re l a tive s t andard devia t ion a tf i ve de t e r mi na ti ons ) o f c a dm i um, c oppe r , l e a d a nd m a nga ne s e a r e 3 . 4% , 3 . 1% , 3 . 9% a nd 3 . 1% , r e s pe c ti ve l y .Keywords: G r a ph i t e f u r na c e a t omi c a bs o r p t i on s pe c t r ome t r y ; M i c r ow a ve i nduc e d n i t r oge n p l a s ma ma s s s pe c t r ome t r y ;S o l i d - l i qu i d e x t r a c t i on s a mpl i ng t e c hn i que ; T r a c e e l e me n t

1 . I n t r o d u c t i o nT h e a d v a n t a g e s o f t h e d i re c t a n a l y s is o f s o l i d

s a m p l e s b y g r a p h i c f u r n a c e a t o m i c a b s o r p t i o n

* Corresponding author.This paper was p resented at the S oli d Sampling Meeting,Amsterdam, November 1994.

s p e c t ro m e t r y ( G F A A S ) h a v e b e e n p o i n t ed o u t b ym a n y a u th o r s [ 1 - 1 0 ] , a n d t h e y c a n b e s u m m a r i z e da s f o l l o w s : ( i ) l o w d e t e c t i o n l i m i t s b a s e d o n t h es o l id , ( i i) s a v i n g o f th e t i m e r e q u i r e d f o r d i s s o l -u t i o n , ( ii i) l o w e r r i s k o f c o n t a m i n a t i o n a n d a n a l y t el o ss e s. H o w e v e r p r o b l e m s a n d d r a w b a c k s o f t h ed i r e c t s o l i d s a m p l i n g t e c h n i q u e s u c h a s t h e d i f f i -c u l t ie s o f t h e s e l e c t i o n o f r e f e r e n c e m a t e r i a l s f o r

0584-854 7/96/$15.00 199 6 Elsevier Science B.V . All rights reservedSSDI 0584- 8547( 95 ) 01348- 2

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212 H. Minami et al./Spectrochimica Acta Part B 51 (1996) 211-220the calibration graph, the use of matrix modifiers,the concentration and dilution of solid samples,automated sample introduction, etc. have pre-viously been pointed out. Many of these problemshave been partially solved by the development ofinstruments and the improvement of analyticalmethodology during the last decade [11-18].The slurry sampling technique has beendeveloped because the introduction of a slurry intothe atomizer is as easy as it is for a liquid sample.Stephen et al. [19] pointed out that the use of slur-ries combines the advantage of solid and liquidsampling. However, it is necessary to use stabiliz-ing agents such as glycerol in order to maintain astable slurry during the time required for sampleintroduction [20-23]. Problems have been reportedwith respect to the use of viscous media in slurrypreparation [6], i.e. the sample aliquot is inef-ficiently pipetted into the atomizer and the samplecan remain around the tube orifice, which canlower the precision.A new solid-liquid extraction sampling tech-nique with GFAAS is based on the quantitativeextraction of the element of interest from powderedbiological samples into the liquid phase. Bendichoand de Loos-Vollebregt [6] have reported that anadvantage of ultrasonication is that the analyte ofinterest is partly extracted into the liquid phase,owing to the ultrasonic action, when the slurriesare prepared in an acidic medium. In this study itwas found that analytes of interest such as cad-mium, copper, lead, manganese, etc., were not justpartly extracted into the liquid phase but werecompletely extracted. In contrast, chromium, iron,etc., were not extracted quantitatively under theseexperimental conditions. The advantage of the pro-posed sampling technique is the separation of thematrix, and it is different from the slurry samplingtechnique because the powdered biological sampleof the solid phase in 1 mol 1 ~ nitric acid solutionis separated from the liquid phase by using a cen-trifuge, and then only the supernatant of the samplesolution is measured. Therefore problems in slurrysample introduction could be solved, because theuse of stabilizing agent becomes unnecessary andthe effect of organic material on the absorbancecould be avoided in this technique.This paper describes a new, simple and rapid

sample preparation method using a solid-liquidextraction sampling technique for the direct deter-mination of cadmium, copper, lead and manganesein powdered biological samples by Zeeman-effectbackground-correction graphite furnace atomicabsorption spectrometry (GFAAS).In addition, this paper describes the determi-nation of the same elements using microwaveinduced plasma-mass spectrometry (MIP-MS),following solid-liquid extraction and dilution withpure water.

2 . E xper i m ent a l2.1. Apparatus

A Hitachi Model Z-8000 Zeeman atomicabsorption spectrometer (Hitachi Ltd., Tokyo,Japan) equipped with a Hitachi AA data processorwas used for the determination of cadmium, lead,copper and manganese. A tube-type graphite fur-nace (o.d. 6.0 mm, i.d. 4.0 mm, length 30 mm) wasused for measurements of cadmium, copper andmanganese. A platform tube and/or laboratory-made type miniature cup [24] was used for themeasurement of lead in NIST Tomato Leaves, etc.A Hitachi Model P-7000, microwave inducedplasma-mass spectrometer (MIP-MS) was alsoused for determinations of these elements.

A Kokusan Model H-103N centrifuge (KokusanCentrifuge Ltd., Tokyo, Japan; max. 4000 revmin-~ for four cups of 100 ml) was used for thecentrifugal separation.

A Branson Model Bransonic 3200 J-4 ultrasoniccleaner (Branson Ultrasonics Corp., Danbury, CT,USA) was used as the ultrasonic agitator for theextraction of the elements of interest.2.2. Solution and materials

All reagents used were analytical grade andMilli-Q water prepared by the Milli-Q water puri-fication system (Millipore Corp., Bedford, USA)was used.Different Reference Materials were obtainedfrom the National Institute of Standards and Tech-

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H . M i n a m i e t a l . / S p e c tr o c h i m i c a A c t a P a r t B 5 1 ( 1 99 6 1 2 1 1 - 2 2 0 2 1 3

n o l o g y ( N I S T , U S A ) , N a t i o n a l R e s e a r c h C o u n c i l( N R C , C a n a d a ) a n d B o w e n ( B o w e n , U K ) .2.3 . Procedure

F o r t h e p r e p a r a t i o n o f s a m p l e s o l u t i o n b y u s i n gt h i s s o l i d li q u i d e x t r a c t i o n t e c h n i q u e , 1 - 1 0 0 m g o fp o w d e r e d b i o l o g i c a l s a m p l e w a s m i x e d i n a c l e a np l as ti c b e a k e r ( 1 0 m l ) w i th 5 . 0 m l o f 1 m o l l ~n i t r i c a c i d b y u s i n g t h e B r a n s o n i c u l t r a s o n i cc l e a n e r f o r 5 m i n a t 4 0 C , a n d t h e n t h e s o l i d p h a s ei n t h e s a m p l e s o l u t i o n w a s s e p a r a t e d f r o m t h el iq u id p h a s e b y c e n t r i f u g in g f o r 1 0 m i n a t4 0 0 0 r e v m i n -~ . T h e s u p e r n a t a n t o f s a m p l e s o l u t io n( 1 0 I~ 1) w a s m e a s u r e d b y G F A A S . A b l a n k s o l -u t i o n w a s a l s o m e a s u r e d u n d e r t h e s a m e c o n -d i t io n s . T h e s u p e r n a t a n t o f s a m p l e s o l u t i o n a n d ab l a n k so l u ti o n w e r e m e a s u r e d b y M I P - M S a f te r 1 0t i m e s o r 1 0 0 t i m e s d i l u t i o n w i t h p u r e w a t e r .

3 . R e s u l t s a n d d i s c u s s i o n

3.1 . Opt im iza t ion o f ins t rumenta l condi t ionsI n o r d e r t o o b t a i n r e p r o d u c i b l e a n d a c c u r a t e a n a -

l y t i c a l r e s u l t s , a s h i n g c o n d i t i o n s w e r e e x a m i n e d i nd e t a il f o r e a c h e l e m e n t b e c a u s e t h e a s h i n g c o n -d i t i o n s a r e m o s t i m p o r t a n t i n G F A A S .

F i g. l ( a ) s h o w s t h e e f f e c t o f a s h in g t e m p e r a t u r eo n c a d m i u m , l e ad , c o p p e r a n d m a n g a n e s ea b s o r b a n c e . I n t h e s o l i d - l i q u i d e x t r a c t i o n t e c h -n i q u e , i t w a s c o n s i d e r e d t h a t n i t r i c a c i d a n de x t r a c t s c o n t a i n i n g m a g n e s i u m , e t c . , a c t a s a m a t r i xm o d i f i e r o n t h e s t a b il i za t i on o f c a d m i u m a n d l e a dd u r i n g t h e a s h i n g s t e p . B e c a u s e p e a k h e i g h t o f c a d -m i u m a n d l e a d a b s o r b a n c e w a s c o n s t a n t b e t w e e n2 0 0 C a n d 5 0 0 C , c o n s t a n t v a l u e s w e r e o b t a i n e db e t w e e n 1 0 0 C a n d 3 5 0 C w h e n s t a n d a r d s o l u t i o n sc o n t a i n i n g 1 m o l 1 j n i tr i c a c i d w e r e m e a s u r e d .T h e r e f o r e m a t r i x m o d i f i e rs w e r e n o t a d d e d f o r t h em e a s u r e m e n t o f c a d m i u m a n d l e a d in th i s c a s e .T h e e f f e c t o f th e a s h i n g t i m e w a s s m a l l a n d c a d -m i u m a n d l e a d a b s o r b a n c e s w e r e c o n s t a n t b e t w e e n1 0 a n d 5 0 s. C o p p e r a n d m a n g a n e s e a b s o r b a n c e so f p e a k a r e a w e r e c o n s t a n t b e t w e e n 2 0 0 C a n d1 0 0 0 C f o r t h e a s h in g t e m p e r a t u r e a s s h o w n i nF i g . l ( a ) , a n d c o p p e r a n d m a n g a n e s e a b s o r b a n c e s

( a )t -

O -

O