Biological Trace Element Research - American Chemical Society

Chapter 14

Direct Analysis of Biological Samples Simultaneous Multielement Analysis—Atomic Absorption Spectrometry with Miniature Cup Solid Sampling

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.ch014

Ikuo Atsuya Kitami Institute of Technology, 165 Koen-cho, 090 Kitami, Japan

Comprehensive studies on the d i r e c t simultaneous determination of trace elements i n some b i o l o g i c a l samples using a simultaneous multielement analysis/atomic absorption spectrometer with a miniature cup-solid sampling technique were c a r r i e d out. Optimum instrumental conditions based on a selection of a n a l y t i c a l l i n e s , heating programs and effects of ashing temperature, were established. For the d i r e c t determination of cadmium, effects of matrix modifier were also examined, and the matrix modification technique was subsequently applied for the d i r e c t simultaneous determination of Cd, Pb and Zn i n c e r t i f i e d reference samples of mussel and hair suplied by the National I n s t i t u t e for Environmental Studies, Japan.

The use of s o l i d sampling technique with atomic absorption spectrometry (AAS) offers high sensitivity, facilitates rapid a n a l y s i s , and minimizes contamination and loss of analytes. However, the direct AAS analysis of s o l i d samples (especially powder samples) is still in its infancy, because of the difficulties encountered with background compensation; with the measurement of peak area absorbance; the introduction of powdered samples i n t o an electrothermal atomizer without l o s i n g the element; and the removal of residues from the atomizer after the measurement. The problems of background compensation and of the measurement of peak area could be solved using Zeeman AAS, and AA data processer respectively (1-3). The introduction of powdered samples into the electrothermal atomizer was also facilitated through the use of small sophisticated containers such as the miniature cup by Atsuya(4-5), platform boat by Kurfurst(6), cup-in-tube by Vollkopf(7). These improvements have stimulated considerable interest on the development of direct AAS analysis of powder samples (8-12); and some new s o l i d sampling techniques involving matrix modification

0097-6156/91/0445-0196$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.


14.

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Multielement Analysis-Atomic Absorption Spectrometry197

(e.g. Ni-H^SO^-HNO^) f o r the d i r e c t d e t e r m i n a t i o n of a r s e n i c ( 1 3 ) , and c h e l a t e - c o p r e c i p i t a t i o n f o r t h e d e t e r m i n a t i o n o f p g / l l e v e l elements from n a t u r a l w a t e r s (14-15). On t h e o t h e r hand, i t has become n e c e s s a r y t o make t h e s y n t h e t i c Standard Reference M a t e r i a l s (SRM), which c o r r e s p o n d t o the s t a n d a r d s o l u t i o n s i n the s o l u t i o n a n a l y s i s , f o r the d i r e c t a n a l y s i s of b i o l o g i c a l samples by t h e s o l i d s a m p l i n g t e c h n i q u e w i t h AAS. We have r e p o r t e d t h a t t h e use o f t h e magnesium o x i n a t e c o p r e c i p i t a t e s as t h e s y n t h e t i c SRM i n s o l i d s a m p l i n g w i t h AAS was s u c c e s s f u l f o r the d i r e c t d e t e r m i n a t i o n of s e v e r a l elements i n b i o l o g i c a l samples of NBS-SRM(16). As a f u r t h e r e x t e n s i o n of our work w i t h s o l i d sampling-AAS, we wish t o r e p o r t here our i n v e s t i g a t i o n s on the f e a s i b i l i t y of d i r e c t simultaneous multielement determination i n v a r i o u s b i o l o g i c a l samples.

EXPERIMENTAL METHODS Apparatus. An H i t a c h i s i m u l t a n e o u s m u l t i - e l e m e n t Zeeman atomic absorption spectrophotometer, Model Z-9000, equipped with a cup-type, g r a p h i t e f u r n a c e , and an H i t a c h i AA d a t a p r o c e s s o r t o measure peak a r e a and peak h e i g h t , and a l s o f o r r e c o r d i n g a b s o r p t i o n p r o f i l e s was used. A M e t t l e r m i c r o b a l a n c e , Model M3, a c c u r a t e t o w i t h i n 1 ;ig was used. A Home-made m i n i a t u r e cup (o.d.,4.8mm; i.d.,4mm; depth,2.5mm; w a l l t h i c k n e s s ,0.4mm; and bottam thickness,0.5mm; see F i g . l ) was used i n c o n j u n c t i o n w i t h the cup-type H i t a c h i f u r n a c e t o overcome problems such as w e i g h i n g s m a l l amounts of powdered samples, i n t r o d u c t i o n of the sample i n t o t h e f u r n a c e w i t h o u t any l o s s of m a t e r i a l and removal of t h e r e s i d u e . The i n c i d e n t l i g h t beam was not b l o c k e d by the m i n i - c u p , which a l s o f a c i l i t a t e s t h e a d d i t i o n of r e a g e n t s such as m a t r i x m o d i f i e r s . A g i v e n m i n i - c u p c o u l d be used f o r a t l e a s t 150 a n a l y s i s . F u r t h e r m o r e , i t was p o s s i b l e t o weigh s e v e r a l by u s i n g s e v e r a l m i n i - c u p s a t t h e same t i m e and measure one a f t e r another s u c c e s s i v e l y because t h e r e were no i n d i v i d u a l d i f f e r e n ces among t h e cups. Home-made f o r c e p s w i t h t a n t a l u m t i p s were used f o r t h e i n s e r t i o n and removal of t h e m i n i - c u p from t h e f u r n a c e . The t i p was bent outwards t o f a c i l i t a t e removal of the m i n i - c u p .

PROCEDURE FOR THE SOLID SAMPLING TECHNIQUE Powdered samples c o n t a i n e d i n t h e m i n i - c u p s were a c c u r a t e l y weighed (0.1-1.5mg) by d i f f e r e n c e u s i n g m i c r o b a l a n c e . Each m i n i - c u p was i n s e r t e d i n t o t h e f u r n a c e u s i n g t h e t a n t a l u m - t i p p e d f o r c e p s and t h e a n a l y t i c a l s i g n a l s were measured u s i n g t h e f u r n a c e AAS. N a t i o n a l Beureau of Standards (now N a t i o n a l I n s t i t u t e of Standard and Technology or NIST) b i o l o g i c a l r e f e r e n c e m a t e r i a l s were used f o r calibration.


198

BIOLOGICAL TRACE ELEMENT RESEARCH


RESULTS AND

DISCUSSION

O p t i m i z a t i o n o f I n s t r u m e n t a l Parameters. For s i n g l e - e l e m e n t d e t e r m i n a t i o n s , i t was p o s s i b l e t o extend the dynamic range of c a l i b r a t i o n c u r v e s by changing the f l o w - r a t e of c a r r i e r gas or s e l e c t i ng a s u i t a b l e a n a l y t i c a l l i n e . For m u l t i - e l e m e n t d e t e r m i n a t i o n s , however, i t was d i f f i c a l t t o extend the dynamic range by changing t h e f l o w - r a t e of c a r r i e r gas, because, f o r example, when the f l o w - r a t e of c a r r i e r gas f o r one element was i n c r e a s e d i n o r d e r t o extend the dynamic c a l i b r a t i o n range, i t became i m p o s s i b l e t o measure another t r a c e l e v e l element. T h e r e f o r e , the f l o w - r a t e of c a r r i e r gas had t o be kept c o n s t a n t ; o n l y the s e l e c t i o n of the a n a l y t i c a l l i n e was p o s s i b l e as shown i n T a b l e I f o r Cd, C r , Cu, Fe, Mn, Pb and Zn. Table I I shows the r e l a t i o n s h i p between a n a l y t i c a l l i n e and dynamic c a l i b r a t i o n range f o r each of t h e s e elements.

Table I . Instrumental c o n d i t i o n s f o r H i t a c h i Multielement Z-AAS

Analytical line(nm)

2

Drying Ashig Atomization

b

Cd,Pb,Zn

Cr,Cu,Fe,Mn

Cd 228.8 Pb 283.3 Zn 307.6

Cr 359.4 Cu 324.8 Fe 373.7 Mn 403.1

80-120°C, 60s 400°C, 60s 2600°C, 7s

600°C, 60s 2600°C, 15s

D r y i n g s t e p was n e c e s s a r y , when the m a t r i x m o d i f i e r was

added.

' C a r r i e r gas f l o w - r a t e , 30ml/min

For the s i m u l t a n e o u s m u l t i e l e m e n t d e t e r m i n a t i o n , the c o n c e n t r a t i o n ranges f o r a n a l y t e s i n samples, which depend on each a n a l y t i c a l l i n e , must b a l a n c e d . Thus, the d i r e c t s i m u l t a n e o u s d e t e r m i n a t i o n of Cd, Pb and Zn i n NBS p i n e n e e d l e s , NIES mussel, and h a i r was p o s s i b l e , s i n c e t h e dynamic ranges f e l l w i t h i n the c e r t i f i e d or p r o v i s i o n a l v a l u e s . I n the d i r e c t s i m u l t a n e o u s a n a l y s i s of b i o l o g i c a l samples by a s o l i d sampling t e c h n i q u e w i t h AAS, the a s h i n g c o n d i t i o n was most i m p o r t a n t . T h e r e f o r e , t h e e f f e c t s of t h e a s h i n g were i n v e s t i g a t e d i n d e t a i l f o r each sample. F i g . l shows t y p i c a l a s h i n g c u r v e s f o r the s i m u l t a n e o u s d e t e r m i n a t i o n of the v o l a t i l e elements, Cd, Pb and Zn i n the NIES mussel r e f e r e n c e sample. Note t h a t the Cd, Pb and Zn absorbances remained c o n s t a n t between 300 and 500°C, 300 and 500°C, and 400 and 700°C, r e s p e c t v e l y ( a l s o see T a b l e I I I ).


14.

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Multielement Analysis-Atomic Absorption Spectrometry

T a b l e I I . R e l a t i o n Between t h e A n a l y t i c a l L i n e and t h e Dynamic Range o f A n a l y t e s Element


Pb

Line (nm)

Relative Sensitivity

283.3 261.4 368.3 213.8 307.6 228.8 326.1 248.3 373.7 359.4 279.5 403.1 324.8 327.4

Zn Cd Fe Cr Mn Cu

1 0.003 0.002 1 0.001 1 0.008 1 0.08 1 1 0.15 1 0.34

Dynamic Range (>g/g)

0.5 200 250 0.03 30 0.02 3.0 4 50 0.5 0.2 3 2 6

-

-

-

50 2000 2500 2.5 350 0.80 100 60 500 10 10 100 80 120

T a b l e I I I . S u i t a b l e A s h i n g Temperature f o r Cd,Pb and Zn Sample NBS SRM Bovine L i v e r and P i n e Needles NIES CRM H a i r and Mussel

Constant r e g i o n of Element a s h i n g temp. (°C)

Recommended a s h i n g temp.(°C)

Cd Pb Zn

300-500 300-500 400-700

300 300 500

Cd Pb Zn

300-500 300-600 300-700

400 500 500

NBS SRM : N a t i o n a l Bureau o f Standards (now N a t i o n a l I n s t i t u t e of Standards and Technology) Standard R e f e r e n c e M a t e r i a l NIES CRM : N a t i o n a l I n s t i t u t e f o r E n v i r o n m e n t a l S t u d i e s C e r t i f i e d Reference M a t e r i a l


199


200


F i g . 2 shows t y p i c a l a s h i n g c u r v e s f o r t h e n o t - s o - v o l a t i l e elements, namely, Cu, C r , Fe and Mn i n t h e NIES h a i r r e f e r e n c e specimen, when n o n - v o l a t i l e elements were measured, t h e c o n d i t i o n o f t h e a s h i n g temperature was n o t s i g n i f i c a n t l y a f f e c t e d by d i f f e r e n c e s i n t h e sample m a t r i x , because o f t h e c o n v e r s i o n o f t h e s e elements t o o x i d e s d u r i n g t h e a s h - c y c l e . The a s h i n g temperature f o r these elements remained c o n s t a n t between 400 and 800°C. Each o f t h e p o i n t s i n F i g . l and F i g . 2 r e p r e s e n t t h e a v e r a ge o f f i v e absorbance measurements based on f i v e d i f f e r e n t sample w e i g h t s . The absorbance v a l u e s p l o t t e d i n t h e s e F i g u r e s were n o r m a l i z e d t o correspond t o lmg of sample. F i g u r e s 1 and 2 a l s o suggest t h a t i t i s p o s s i b l e t o s i m u l t a n e o u s l y determine v o l a t i l e and n o n - v o l a t i l e elements. However, we d i d n o t i n v e s t i g a t e t h i s idea further. T a b l e s IV and V p r e s e n t t h e a n a l y t i c a l r e s u l t s f o r Cd, Pb and Zn i n NIES mussel and h a i r , r e s p e c t i v e l y . The samples were a n a l y z e d w i t h , and w i t h o u t m a t r i x m o d i f i e r s . The m o d i f i e r s used were 4NH2S0^ and 10MHNO~. The s e l e c t i o n o f a s u i t a b l e m a t r i x m o d i f i e r was n o t easy. "For example, o n l y 4NH^S0^ (5ml) proved s u i t a b l e f o r Cd i n NIES mussel and h a i r ; even n e r e , t h e r e s u l t s agreed w i t h t h e c e r t i f i e d v a l u e s o n l y when NBS p i n e n e e d l e s were used f o r c a l i b r a t i o n . The r e s u l t s were poor w i t h NBS bovine l i v e r as a c a l i b r a t i o n s t a n d a r d ( T a b l e s IV and V ) .

T a b l e IV. D i r e c t i n NIES Mussel

Simultaneous D e t e r m i n a t i o n o f Cd,Pb and Zn Standard f o r

Proposed

method (ug.g-1>)

Method

calibration

Cd

Pb

Zn

without matrix modifier

NBS Oyster Tissue P i n e Needles Bovine L i v e r

a 0.6610.10 0.7510.11

0.8510.06 0.8710.06 0.7610.05

97.61 3.7 90.61 6.9 91.01 5.7

w i t h 4N-H S0, ζ 4

P i n e Needles Bovine L i v e r

0.8510.09 0.6410.06

0.7110.09 1.0010.12

257 108

w i t h 10N-HN0,

Tomato Leaves P i n e Needles Bovine L i v e r

a 0.7110.07 0.5910.06

0.8410.07 0.9910.08 0.8310.07

81 78 84

0.8210.03

0.9110.04

106

o

C e r t i f i e d values: CL

not

determined


126 ill 1 1 1 1 6


14.

ATSUYA

2.0

Multielement Analysis-Atomic Absorption Spectrometry201

r-

Fe -oCu

Nn Cr

—o 1_ 400

l_ 600 Temperature (°C)

-O_J

-J 0

800

F i g u r e 2. E f f e c t o f a s h i n g t e m p e r a t u r e on C r , Cu, Fe and Mn i n NIES H a i r Cr 359.4nm, Cu 324.8nm, Fe 373.7nm, Mn 403.lnm


202



For Zn, good agreement was o b t a i n e d w i t h c e r t i f i e d v a l u e s when H^SO^ was used as the m o d i f i e r and NBS bovine l i v e r as the c a l i b r a t i o n s t a n d a r d ( T a b l e s IV and V ) . Use of HNO^ ( 5 u l ) was a l s o s a t i s f a c t o r y f o r d e t e r m i n i n g Cd i n NIES h a i r , but was u n s u i t a b l e f o r Pb and Zn i n NIES h a i r ( T a b l e V) and Zn i n NIES mussel (Table IV) due t o the severe d i s t o r t i o n of the a b s o r p t i o n p r o f i l e ; t y p i c a l examples a r e shown i n F i g . 3 w i t h NIES h a i r and NBS tomato l e a v e s as m a t r i c e s . I t i s c l e a r t h a t t h e s e m o d i f i e r s a r e not s u i t a b l e f o r the d i r e c t s i m u l t a n e o u s d e t e r m i n a t i o n of Cd, Pb and Zn i n NBS tomato l e a v e s and NIES h a i r .

T a b l e V. D i r e c t Simultaneous i n NIES H a i r Standard

for

D e t e r m i n a t i o n of Cd,Pb and Proposed

method (jig.g

Zn ^)

Method

calibration

Cd

Pb

without matrix modifier

NBS Oyster Tissue P i n e Needles Bovine L i v e r

a 0. 2310.02 0. 1710.02

5.0±0.3 7.410.4 5.610.3

157110 134113 1511 8

w i t h 4N-H S0, 2 4

Pine needles Bovine L i v e r

0. 2110.03 0. 1610.02

6.710.7 9.510.9

372125 156111

w i t h 10N-HN0,

P i n e Needles Bovine L i v e r

0. 1910.03 0. 1610.02

b b

b b

o

C e r t i f i e d v a l u e s : 0.2010.03 not

(6.0)

Zn

169H0

determined

h i g h l y di storted absorption p r o f i l e s

For t h i s r e a s o n , NBS tomato l e a v e s were not used as c a l i b r a t i o n s t a n d a r d s i n the p r e s e n t work. I t was n e c e s s a r y t o use m a t r i x m o d i f i e r s f o r Cd because of i t s p o t e n t i a l f o r l o s s d u r i n g the a s h - c y c l e . A l s o the 307.6nm l i n e had t o be used f o r Zn because i t was i m p o s s i b l e t o i n c r e a s e the c a r r i e r gas f l o w - r a t e when doing simultaneous multielement analyses. A l t h o u g h the n o t - s o - v o l a t i l e elements ( C r , Cu, Fe, Mn) posses s v a r i o u s a n a l y t i c a l l i n e s , the d i f f i c u l t i e s w i t h t h e c o n c e n t r a t i o n ranges of the a n a l y t e s and a l s o i n o b t a i n i n g s u i t a b l e s t a n d a r d m a t e r i a l s f o r c a l i b r a t i o n remained. These a n a l y t e s were, however, s t a b l e d u r i n g the a s h - c y c l e and t h e r e f o r e , i t was f e l t t h a t d i r e c t s i m u l t a n e o u s d e t e r m i n a t i o n w i t h s o l i d sampling-AAS might be f e a s i b l e . The r e s u l t s a r e shown i n Table VI f o r t h e s e elements i n NIES mussel and h a i r . No m a t r i x m o d i f i e r s were r e q u i r e d .



14.

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Multielement Analysis—Atomic Absorption Spectrometry 203

NIES

NBS Tomato Leaves (A)

(A)

(B)

0.5

Hair (B)

0.1 Η

. λ

. L

0

J l

0.2 0.2 J

0.05 H

- j

0.05 " Zn

ο-JL· IJL

Λ1 -L

0 Time, sec.

5 0 5 Time, sec.

F i g u r e 3. A b s o r p t i o n p r o f i l e s f o r Cd, Pb and Zn i n NBS Tomato Leaves and NIES H a i r w i t h (A) 10N-HNC> (B) 4N-H S0 3

NBS Tomato Leaves A (0.393mg) NIES H a i r A (0.484mg)

2

4

Β (0.412mg) Β (0.502mg)


204


Table V I . D i r e c t Simultaneous Mn i n NIES Mussel and H a i r

D e t e r m i n a t i o n o f Cr,Cu,Fe and

NIES

Standard f o r

Proposed method (/ig g - )

Sample

calibration


a

not

Cr

Cu

Fe

Mn

NBS O y s t e r T i s s u e 0.59±0.16 Orchard Leaves 0.74±0.20 C i t r u s Leaves 0.80±0.22

5.1±0.3 6.2±0.3 6.5±0.4

158±12 160±12 157±12

16.4±1.6 16.3±1.6 15.9±1.6

C e r t i f i e d v a l u e s : 0.63±0.07

4.9±0.3

158± 8

16.3±1.2

±0.3 ±0.3 ±0.4 ±0.4

16.2±0.7 19.6±0.8 20.8±0.9 17.8±1.2

242±14 245±14 241±14 250± 9

5.1±0.8 5.0±0.7 4.9±0.7 a

C e r t i f i e d v a l u e s : 1.4 ±0.2

16.3±1.2

225± 9

5.2±0.3

Mussel

Hair

1

NBS Oyster Tissue Orchard Leaves C i t r u s Leaves P i n e Needles

1.1 1.4 1.5 1.5

determined

Good agreement w i t h c e r t i f i e d v a l u e s was o b t a i n e d f o r a l l t h e f o u r elements i n NIES mussel when NBS o y s t e r t i s s u e was used as t h e c a l i b r a t i o n s t a n d a r d . Indeed, f o r Fe and Mn, NBS o r c h a r d l e a v e s and c i t r u s l e a v e s were e q u a l l y good c a l i b r a t i o n m a t r i c e s . In t h e case o f t h e NIES h a i r sample, e x c e l l e n t agreement w i t h c e r t i f i e d v a l u e s was o b t a i n e d f o r a l l t h e f o u r elements i r r e s p e c t i v e o f t h e NBS c a l i b r a t i o n s t a n d a r d used.

CONCLUSION Two c o n d i t i o n s f o r t h e d i r e c t s i m u l t a n e o u s determination of m u l t i - e l e m e n t s by AAS w i t h a s o l i d sampling t e c h n i q u e had t o be s a t i s f i e d : The f i r s t was i n f i n d i n g a s u i t a b l e a s h i n g tempera t u r e . I n o r d e r t o f i n d t h e most s u i t a b l e a s h i n g temperature, i t was necessary t o examine t h e e f f e c t s o f t h e a s h i n g temperature i n d e t a i l f o r each sample. S i n c e t h e v o l a t i l i t y o f a n a l y t e s depended on t h e sample, t h e a s h i n g c o n d i t i o n had t o be v a r i e d a c c o r ding t o the d i f f e r e n c e of the chemical s p e c i e s even i f t h e a n a l y t e was t h e same. The second c o n d i t i o n was t h e r e s t r i c t i o n of t h e c o n c e n t r a t i o n range f o r t h e measurement o f a n a l y t e s , and because o f t h i s , i t was i m p o r t a n t t o aim a t one sample and t o f i n d a s u i t a b l e c o m b i n a t i o n o f elements i n b i o l o g i c a l samples f o r t h e d i r e c t s i m u l t a n e o u s a n a l y s i s . A l s o , when t h e m a t r i x modifi c a t i o n t e c h n i q u e was a p p l i e d f o r t h e d e t e r m i n a t i o n o f an element such a s cadmium, t h e e f f e c t o f t h e m a t r i x m o d i f i e r on o t h e r elemen t s such a s l e a d , z i n c , e t c , had t o be examined. We c o n s i d e r t h a t s i n g l e - e l e m e n t d e t e r m i n a t i o n i s p r e f e r a b l e t o m u l t i e l e m e n t d e t e r m i n a t i o n f o r Cd because o f t h e need t o use m a t r i x m o d i f i e r s .


14. ATSUYA

Multielement Analysis—Atomic Absorption Spectrometry

ACKNOWLEDGMENTS The author w i s h s t o thank Mr. K.Abe, machinery e n g i n e e r o f K i t a m i I n s t i t u t e o f Technology, f o r h i s g r e a t e f f o r t s t o make our m i n i a t u r e cups. The a u t h o r i s g r a t e f u l t o t h e M i n i s t r y o f E d u c a t i o n , Japan, f o r a r e s e a r c h g r a n t (No.C-01540465).

LITERATURE CITED 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.ch014

(1) Koizumi,H.; Yasuda,K. Anal.Chem. 1975, 47, 1679-82. (2) Koizumi,H.; Yasuda,K.; Katayama,M. Anal.Chem. 1977, 49, 1106-12. (3) Koizumi,H. Anal.Chem. 1987, 50, 1101-05. (4) Atsuya,I.; Itoh,K. Spectrochim.Acta 1983, 38B, 1259-64. (5) Atsuya,I.; Itoh,K. Bunseki Kagaku 1982, 31, 708-12. (6) Kurfurst,U. Fresenius'Z.Anal. 1983, 316, 1-5. (7) Vollkopf,U.; Grobenski,Z.; Tamm.; Welz,Β. Analyst(London), 1985, 110, 573-77. (8) Atsuya,I.; I t o h , K . ; Akatsuka,K. Fresenius'Ζ.Anal.Chem. 1987, 328, 338-841 (9) Grobecker,Κ.Η.; Klussendorf,B. Fresenius'Ζ.Anal.Chem. 1985, 322, 673-77. (10) I t o h , K . ; Akatsuka,K.; Atsuya,I. Bunseki Kagaku 1984, 33, 301-05. (11) I t o h , K . ; Akatsuka,K.; Atsuya,I. Bunseki Kagaku 1986, 35, 122-27. (12) Rosopulo,A.; Grobecker,Κ.Η.; Kurfurst,U. Fresenius'Ζ.Anal.Chem. 1984, 319, 540-44. (13) Atsuya,I.; Itoh,K.; Akatsuka,K.; Jin,K. Fresenius'Z.Anal.Chem. 1987, 326, 53-56. (14) Akatsuka,K.; Atsuya,I. Fresenius'Ζ.Anal.Chem. 1987, 329, 453-57. (15) Atsuya,I.; Itoh,K. Fresenius'Ζ.Anal.Chem. 1988, 329, 750-55. (16) Akatsuka,K.; Atsuya,I. Anal.Chem. 1989, 61, 216-20. (17) E d i g e r , R . D . ; Peterson.G.E.; Kerber,J.D. At.Absorp.Newslet t, 1974, 13, 61-65. RECEIVED July 16, 1990


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