Chapter 15
Arsenic, Bismuth, Copper, Lead, Nickel, and Selenium in Some Biological Samples Determination by Graphite Furnace Atomization—Atomic Absorption Spectrometry 1
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Ni Zhe-ming , Shan Xiao-Quan , Jin Long-Zhu , Luan Shen , Zhang Li , and K. S. Subramanian Downloaded by NORTH CAROLINA STATE UNIV on August 2, 2012 | http://pubs.acs.org Publication Date: December 26, 1991 | doi: 10.1021/bk-1991-0445.ch015
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Research Center for Eco-Environmental Sciences, Academia Sinica, P.O. Box 934, Beijing, China Environmental Health Centre, Health and Welfare Canada, Tunney's Pasture, Ottawa, Ontario K1A 0L2, Canada 2
Graphite furnace atomic absorption spectrometric (GFAAS) methods have been developed for determining As, Bi, Cu, Ni, Pb and Se in urine; Al and L i in whole blood and serum; and Ni in some biological reference materials. Cu and Ni were separated from the urine matrix by coprecipitation with ammonium pyrrolidinedithiocarbamate (APDC); Bi and Pb were extracted with potassium iodide-methyl isobutylketone (KI-MIBK) and APDC-MIBK, respectively. The analytical sensitivities of these elements in the organic media were significantly improved when Pd was used as a matrix modifier. The spectral interference, which occurred in the determination of Se in urine, was eliminated by adding Rh. Improved sensitivities were obtained for As and Se in blood when the hydrides were deposited on Pd-coated graphite tubes prior to atomization. Aluminum was determined in blood using potassium dichromate as a matrix modifier. The use of Ta-coated graphite tube significantly minimized the memory effect and improved the sensitivity for Li determination. Subramanian has c o m p r e h e n s i v e l y r e v i e w e d t h e d e t e r m i n a t i o n o f t r a c e elements i n human body f l u i d s by GFAAS ( 1 , 2 ) . GFAAS i s u n d o u b t e d l y one o f t h e most s e n s i t i v e and c o n v e n i e n t a n a l y t i c a techniques. The use o f modern f u r n a c e t e c h n o l o g y , e s p e c i a l l y s t a b i l i z e d temperature p l a t f o r m f u r n a c e a t o m i z a t i o n (STPF), i s recommended f o r o b t a i n i n g r e l i a b l e r e s u l t s (see Subramanian, this issue). However, f i n a n c i a l c o n s i d e r a t i o n s o f t e n p r e v e n t us from u s i n g t h e STPF t e c h n o l o g y as i t r e q u i r e s t h e use o f e x p e n s i v e p y r o c o a t e d g r a p h i t e t u b e s and p l a t f o r m s , and Zeeman background c o r r e c t i o n . T h e r e f o r e , we chose a l t e r n a t e approaches t h a t do n o t i n v o l v e t h e use o f t h e s e e x p e n s i v e components, and s t i l e n s u r e t h e q u a l i t y o f o u r d a t a . In t h i s paper, we r e p o r t o u r GFAAS methods f o r d e t e r m i n i n g As, B i , Cu, N i , Pb and Se i n human u r i n e , and A l and L i i n human whole b l o o d and serum. We d e v e l o p e d o u r methods u s i n g a P e r k i n - E l m e r Model 4000 atomic a b s o r p t i o n s p e c t r o p h o t o m e t e r e q u i p p e d w i t h a HGA 400 g r a p h i t e f u r n a c e , and a Model 056 s t r i p c h a r t r e c o r d e r f o r 0097-6156/91/0445-0206$06.00/0 © 1991 American Chemical Society
In Biological Trace Element Research; Subramanian, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.
15.
ZHE-MING ET AL.
AS, BI, CU, PB, NI, and SE in Biological Samples
m e a s u r i n g a n a l y t e a b s o r b a n c e s under power' c o n d i t i o n s .
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DETERMINATION OF GFAAS
N i AND
Cu
*gas s t o p ' and
IN URINE BY
^maximum
APDC COPRECIPITATION-
The IUPAC Subcommittee on E n v i r o n m e n t a l and O c c u p a t i o n a l T o x i c o l o g y o f N i c k e l has p r o p o s e d a r e f e r e n c e method f o r d e t e r m i n i n g N i i n serum and u r i n e (3.) . The r e f e r e n c e method i n v o l v e d d e c o m p o s i t i o n o f t h e sample by a c i d - d i g e s t i o n ; d i l u t i o n o f t h e d i g e s t a t e f o l l o w e d by pH adjustment t o 7 w i t h ammonium h y d r o x i d e ; a d d i t i o n o f APDC; e x t r a c t i o n o f t h e Ni-PDC c h e l a t e w i t h MIBK; and measurement o f t h e N i c o n c e n t r a t i o n i n MIBK by GFAAS. However, t h e c h e l a t e i n t h e o r g a n i c l a y e r was not s t a b l e and t e n d e d t o decompose g r a d u a l l y upon s t o r a g e . T h e r e f o r e , i n our method, N i i n t h e d i g e s t a t e was p r e c o n c e n t r a t e d and s e p a r a t e d from t h e u r i n e m a t r i x by p r e c i p i t a t i o n w i t h APDC (±) . Q u a n t i t a t i v e r e c o v e r y ( 9 8 - 1 0 3 % ) was a c h i e v e d i n a s i n g l e p r e c i p i t a t i o n o v e r a wide a c i d i t y range
(0.08-2.0
Μ HN0 , 3
or
0.05-0.9
M
HCL0 ) ; f i v e different 4
u r i n e samples (endogenous N i l e v e l = 0 . 5 t o 2 . 2 ng/ml) were t e s t e d and each sample was s p i k e d w i t h 4 ng N i / m l . The Ni-PDC p r e c i p i t a t e was d i s s o l v e d i n a minimum amount o f MIBK and N i was measured a t t h e r e s o n a n c e l i n e o f 2 3 2 . 0 nm. The Ni-PDC i n MIBK was f o u n d t o be s t a b l e f o r a t l e a s t a week a t ambient temperature. T h i s f e a t u r e i s a t t r a c t i v e f o r c l i n i c a l and e n v i r o n m e n t a l l a b o r a t o r i e s w i t h a l a r g e sample t h r o u g h p u t . The above method was a l s o a p p l i e d f o r d e t e r m i n i n g N i i n t h r e e NIST s t a n d a r d r e f e r e n c e m a t e r i a l s : o r c h a r d l e a v e s (SRM 1 5 7 1 ) , wheat f l o u r (SRM 1 5 6 7 ) and r i c e f l o u r (SRM 1 5 6 8 ) . Our values of 1 . 2 , 0.18, and 0 . 1 6 mg/Kg a g r e e d w e l l w i t h t h e c e r t i f i e d values of 1 . 3 , 0.18, and 0 . 1 6 mg/Kg, r e s p e c t i v e l y (,4) . The sample w e i g h t s t a k e n f o r a n a l y s i s were 2 0 , 5 0 , and 5 0 mg, r e s p e c t i v e l y . The method f o r N i d e s c r i b e d above was a l s o a d a p t e d f o r d e t e r m i n i n g Cu i n u r i n e (4_) . The Cu-PDC was q u a n t i t a t i v e l y p r e c i p i t a t e d from 0 . 2 - 2 . 0 M p e r c h l o r i c a c i d . The r e c o v e r y o f Cu from f i v e d i f f e r e n t samples s p i k e d w i t h 10 ng Cu/ml was 93105%. The endogenous Cu l e v e l s i n t h e s e samples were 6 . 7 - 1 6 . 3 ng/ml. We a l s o d e t e r m i n e d Cu i n t h e u r i n e o f a n e p h r i t i c p a t i e n t ; t h e v a l u e was f o u n d t o be 1 2 9 ng/ml. To d e t e c t such h i g h l e v e l s , a 0 . 2 - m l u r i n e a l i q u o t was s u f f i c i e n t . DETERMINATION OF
B i IN URINE BY
IODIDE-MIBK-GFAAS
The c o n c e n t r a t i o n o f B i i n u r i n e c o l l e c t e d from l o c a l v o l u n t e e r s was f o u n d t o be 0 . 0 2 - 0 . 0 7 ng/ml. The d e t e r m i n a t i o n o f such low l e v e l s r e q u i r e s some form o f p r e c o n c e n t r a t i o n . We u s e d a s o l v e n t e x t r a c t i o n p r o c e d u r e (,5) . B i was e x t r a c t e d w i t h MIBK from u r i n e samples c o n t a i n i n g i o d i d e and h y d r o c h l o r i c a c i d , and d e t e r m i n e d by GFAAS. As shown i n F i g . l , t h e peak h e i g h t absorbance s i g n a l o f B i i n MIBK was v e r y low even a t a c h a r r i n g t e m p e r a t u r e o f 200°C p r o b a b l y due t o v o l a t i l i z a t i o n o f Bi. However, i n t h e p r e s e n c e o f Pd, t h e s e n s i t i v i t y was g r e a t l y enhanced; a l s o t h e c h a r r i n g t e m p e r a t u r e c o u l d be r a i s e d up t o 1000°C w i t h o u t any l o s s o f B i p r o b a b l y due t o t h e f o r m a t i o n o f t h e r m a l l y s t a b l e i n t e r m e t a l l i c compounds. The method was s u c c e s s f u l l y a p p l i e d f o r d e t e r m i n i n g sub-ng/ml l e v e l s o f B i i n s i x u r i n e samples; t h e v a l u e s r a n g e d from 0.020 . 0 7 ng/ml. At s u p p l e m e n t a l l e v e l s o f 0 . 0 5 - 0 . 2 0 ng/ml, t h e r e c o v e r y o f B i was q u a n t i t a t i v e ( 9 0 - 9 8 % ) from t h e s e samples.
In Biological Trace Element Research; Subramanian, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.
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BIOLOGICAL TRACE ELEMENT RESEARCH
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D E T E R M I N A T I O N OF P b I N U R I N E BY A P D C - M I B K - G F A A S U n l i k e i n t h e c a s e o f N i a n d C u , t h e P b - P D C c h e l a t e was s t a b l e i n MIBK u p o n s t o r a g e . T h e r e f o r e , t h e l e s s cumbersome s o l v e n t e x t r a c t i o n p r o c e d u r e was a d o p t e d (6,) . F i g . 2 shows t h e p e a k h e i g h t a b s o r b a n c e o f P b i n MIBK a s a f u n c t i o n o f c h a r r i n g temperature. The absorbance i n i t i a l l y i n c r e a s e d w i t h i n c r e a s i n g c h a r r i n g t e m p e r a t u r e a n d r e a c h e d a maximum a t 800°C; b e y o n d 800°C, h o w e v e r , t h e r e was a r a p i d d e c r e a s e i n absorbance. T h i s phenomenon s u g g e s t e d t h a t a t l o w e r c h a r r i n g t e m p e r a t u r e s t h e P b c h e l a t e was p a r t i a l l y d e c o m p o s e d t o a t h e r m a l l y s t a b l e compound. At the charring temperature of 800°C t h e d e c o m p o s i t i o n was n e a r l y c o m p l e t e , a n d t h e r e f o r e a maximum o c c u r r e d . With f u r t h e r i n c r e a s e i n temperature, t h e Pb atoms were l o s t f r o m t h e g r a p h i t e f u r n a c e a n d t h e peak h e i g h t absorbance decreased. H o w e v e r , when P d was u s e d a s a m o d i f i e r , a c h a r r i n g t e m p e r a t u r e o f 1200°C c o u l d b e t o l e r a t e d ; a l s o t h e s e n s i t i v i t y was h i g h e r . T h e r e f o r e P d was e m p l o y e d a s a m a t r i x m o d i f i e r f o r s u c c e s s f u l ! / d e t e r m i n i n g Pb i n u r i n e . The a d v a n t a g e o f t h e h i g h c h a r r i n g t e m p e r a t u r e was t h a t t h e u r i n e m a t r i x c o u l d be burned o f f t h e r e b y m i n i m i z i n g i n t e r f e r e n c e . The Pb v a l u e s d e t e r m i n e d i n n i n e u r i n e samples were f o u n d t o be 2, 4, 6, 8, 12, 19, 26, 40 a n d 60 n g / m l , respectively. D E T E R M I N A T I O N OF S e I N U R I N E BY G F A A S MODIFICATION
U S I N G RHODIUM M A T R I X
T h e G F A A S d e t e r m i n a t i o n o f S e i n human u r i n e i s c o m p l i c a t e d because of i t s high v o l a t i l i t y , interaction with the graphite surface, and s p e c t r a l and chemical interference (2). Se i s p a r t i a l l y l o s t a t t e m p e r a t u r e s a b o v e 300°C. N i c k e l (2) or p a l l a d i u m (_8) h a s b e e n u s e d a s a m o d i f i e r t o s t a b i l i z e S e u p t o a c h a r r i n g t e m p e r a t u r e o f 1200°C. However, t h e s e m o d i f i e r s c o u l d n o t overcome t h e s p e c t r a l i n t e r f e r e n c e o r i g i n a t i n g from t h e d e c o m p o s i t i o n p r o d u c t s o f i r o n a n d p h o s p h o r u s s a l t s (9,
10 ) . The c a l c i u m p h o s p h a t e p r e s e n t i n u r i n e c a u s e d a n e g a t i v e i n t e r f e r e n c e a t t h e 196.0 nm S e r e s o n a n c e l i n e a n d t h i s could not be compensated f o r u s i n g t h e deuterium background c o r r e c t o r (9, 1 0 ) . The i n t e r f e r e n c e presumably o r i g i n a t e d from m o l e c u l e s s u c h a s P O , P O , a n d P w i t h i n t h e n a r r o w v i c i n i t y o f t h e Se l i n e (10). T h e a d d i t i o n o f P t was f o u n d t o r e m o v e t h i s i n t e r f e r e n c e b y f a c i l i t a t i n g t h e f o r m a t i o n o f Ρ atoms a n d thereby decreasing the spectral interference. However, o u r e x p e r i m e n t a l r e s u l t s i n d i c a t e d t h a t t h e amount o f P t o r P d a d d e d t o t h e s a m p l e s h o u l d b e >100 μ g . Such h i g h amounts s i g n i f i c a n t l y s u p p r e s s e d t h e Se s i g n a l a s shown i n F i g . 3 ( b , b' ; c, c ' ) . We f o u n d t h a t t h e a d d i t i o n o f R h i n s t e a d o f P t o r P d n o t o n l y s t a b i l i z e d S e u p t o 1200°C ( F i g . 4 ) , b u t a l s o h e l p e d overcome t h e s p e c t r a l i n t e r f e r e n c e (Fig. 3a, a ' ) . Note from F i g . 3 (a, a') that, u n l i k e i n the case of Pt and Pd, t h e r e was n o l o s s o f s e n s i t i v i t y e v e n a t 100 μ g R h . Therefore, we w e r e a b l e t o d e v e l o p a r a p i d a n d r e l i a b l e m e t h o d f o r d e t e r m i n i n g S e i n human u r i n e u s i n g d e u t e r i u m b a c k g r o u n d c o r r e c t i o n i n the presence of Rh. T a b l e I s u m m a r i z e s t h e a n a l y t i c a l r e s u l t s f o r Se i n NIST r e f e r e n c e u r i n e s a m p l e s (SRM 2 670) a n d a l s o i n f i v e human u r i n e s a m p l e s u s i n g Rh m a t r i x m o d i f i c a t i o n . G o o d a g r e e m e n t was o b t a i n e d w i t h t h e NIST c e r t i f i e d v a l u e s a t t e s t i n g t o t h e accuracy of our method. The Se v a l u e s i n t h e f i v e u r i n e s a m p l e s r a n g e d f r o m 49 t o 77 n g / m l . +
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In Biological Trace Element Research; Subramanian, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.
15.
AS, BI, CU, PB, NI, and SE in Biological Samples
ZHE-MINGETAL.
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0.12
0
200 400 600
800 1000 1200 1400
CHARRING TEMPERATURE,°C Fig.
1.
E f f e c t o f P a l l a d i u m on t h e C h a r r i n g Temperature o f Bismuth. (0) 0.4 ng B i i n MIBK; (A) 0.5 ng B i i n aqueous s o l u t i o n ; (·) 0.4 ng B i i n MIBK + 1 μ g Pd; (A) 0.5 ng B i i n aqueous s o l u t i o n + 0.8 μg Pd. (Reproduced w i t h p e r m i s s i o n f r o m R e f . 5. C o p y r i g h t 1981 P o l y s c i e n c e P u b l i c a t i o n , Inc.)
0.20
tu Ο Ζ
ο
0.15
-ο
ο- ο- - ο
< g
ο / m
