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Suitability of Various Filtering Media for the Collection and Determination of Organoarsenicals in Air GREG RICCI, GEORGE COLOVOS, NORMAN HESTER, and L. STANLEY SHEPARD Rockwell International Environmental Monitoring and Services Center, Newbury Park, CA 91320 JANET C. HAARTZ National Institute for Occupational Safety and Health, Cincinnati, OH 45226
The use of arsenic and its organic derivatives as herbicides, pesticides, and wood preservatives has been increasing steadily each year. Large quantities of arsenical compounds are manufactured by the chemical industry and eventually find their way into the environment (1). About seventy percent of these chemicals are inorganic in form and the rest are organoarsenicals (2). Of the organoarsenicals, the most important species from the point of view of use and health effects are monomethylarsonic acid (MMA), dimethylarsenic acid (DMA), and p-aminophenylarsonic acid (p-APA). Accurate estimates of worker exposure to organoarsenicals have not been possible because: 1) extensive studies of collection media for sampling organoarsenicals in air have not been performed; and 2) ruggedized analytical techniques capable of distinguishing between the different inorganic and organic species present in a sample have not been available. A number of analytical techniques have recently been reported for analyzing mixtures of various arsenicals (2-9). Although the sensitivity of these techniques is excellent, most are unsuitable to use for routine application either because of poor precision and incomplete recoveries, or because they are too tedious and time consuming. We h a v e d e v e l o p e d a h i g h l y s e n s i t i v e , a u t o m a t e d t e c h n i q u e f o r s e p a r a t i n g a n d a n a l y z i n g a r s e n i c ( i l l ) , a r s e n i c ( V ) , MMA, DMA, a n d p-APA i n s o l u t i o n . T h e t e c h n i q u e s e p a r a t e s t h e components u s i n g i o n exchange chromatography f o l l o w e d b y c o n t i n u o u s g e n e r a t i o n o f t h e a r s i n e d e r i v a t i v e s a n d a t o m i c a b s o r p t i o n d e t e c t i o n (10.). The d e v e l o p e d s y s t e m p r o v i d e s a n e x c e l l e n t means o f a n a l y s i s o f e n v i r o n m e n t a l s a m p l e s and h a s b e e n a p p l i e d d i r e c t l y t o t h e d e t e r m i n a tion of organoarsenicals i n a i r . I n t h e p r e s e n t s t u d y , s a m p l i n g o f b o t h p a r t i c u l a t e and v a p o r f o r m s o f MMA, DMA, a n d p - A P A was i n v e s t i g a t e d a n d i t was f o u n d t h a t t h e s e compounds e x i s t i n a i r m o s t l y i n t h e p a r t i c u l a t e f o r m .
0097-6156/81/0149-03 8 3$05.00/ 0 © 1981 American Chemical Society
In Chemical Hazards in the Workplace; Choudhary, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
384
CHEMICAL HAZARDS IN THE WORKPLACE
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C o l l e c t i o n o f a i r b o r n e p a r t i c u l a t e s i n workplace atmospheres can be achieved e f f e c t i v e l y by a v a r i e t y o f f i l t e r i n g media which are amenable t o use w i t h p e r s o n a l s a m p l i n g d e v i c e s . E x t r a c t i o n o f the p a r t i c u l a t e s from the f i l t e r s w i t h s u i t a b l e s o l v e n t s r e s u l t s i n s o l u t i o n s w h i c h may t h e n b e a n a l y z e d b y t h e d e v e l o p e d a n a l y t i c a l technique. T h r e e c o m m e r c i a l l y a v a i l a b l e f i l t e r i n g media were e v a l u a t e d for the c o l l e c t i o n o f airborne p a r t i c u l a t e s of the organoarsenical compounds. These were: c e l l u l o s e e s t e r , F l u o r o p o r e , and M i t e x membrane f i l t e r s . T h e e v a l u a t i o n was b a s e d o n t h e f o l l o w i n g r e quirements: l ) t h e c o l l e c t i o n medium must q u a n t i t a t i v e l y c o l l e c t t h e p a r t i c u l a t e s ; 2) t h e c o l l e c t i o n medium must b e c a p a b l e o f r e t a i n i n g t h e compounds w i t h o u t l o s s o r c h e m i c a l c h a n g e b e f o r e a n a l y s i s ; 3) t h e c o l l e c t e d s p e c i e s must b e e x t r a c t e d q u a n t i t a t i v e l y f r o m t h e c o l l e c t i o n medium f o r a n a l y s i s ; a n d h) t h e m e t h o d must b e e f f i c i e n t a t t e m p e r a t u r e s u p t o 50°C a n d a r e l a t i v e h u m i d i t y o f 95%* I n t h e c o u r s e o f t h e s t u d i e s , t h e c e l l u l o s e e s t e r f i l t e r s were found t o r e a c t w i t h c e r t a i n s p e c i e s and t h e M i t e x f i l t e r s were found not to c o l l e c t the p a r t i c u l a t e s e f f e c t i v e l y . Fluoropore membrane f i l t e r s were f o u n d t o b e t h e most e f f e c t i v e medium f o r c o l l e c t i o n of particulate organoarsenicals. The c o m p l e t e s a m p l i n g and a n a l y s i s p r o c e d u r e was t e s t e d f o r p r e c i s i o n a n d a c c u r a c y u s i n g f i l t e r samples l o a d e d i n a dynamic a e r o s o l g e n e r a t i o n and s a m p l i n g system t o s i m u l a t e workplace atmospheres ( l l ) . The r e s u l t s have shown t h e d e v e l o p e d m e t h o d t o b e v e r y p r e c i s e a n d a c c u r a t e f o r c o n c e n t r a t i o n s r a n g i n g f r o m 5-20 ug As/m3. i t h i s paper, the s t u d i e s conducted f o r the s e l e c t i o n o f an a p p r o p r i a t e f i l t e r i n g medium a n d t h e e v a l u a t i o n o f t h e c o m b i n e d s a m p l i n g a n d a n a l y s i s method a r e p r e s e n t e d . n
Experimental The h i g h l y s e n s i t i v e automated a n a l y t i c a l method u t i l i z e d f o r t h e d e t e r m i n a t i o n o f MMA, DMA, p - A P A , A s ( l I I ) , a n d A s ( V ) h a s b e e n d i s c u s s e d i n d e t a i l elsewhere ( l O j . The o p t i m i z e d p r o c e d u r e f o r the determination o f organoarsenicals i n a i r i s described below. Sampling Procedure. Atmospheric p a r t i c u l a t e matter i s c o l l e c t e d q u a n t i t a t i v e l y o n 37mm membrane f i l t e r s . T h i s i s done by sampling a i r at t h e r a t e o f about 1.5 l i t e r s per minute t h r o u g h a t h r e e - p i e c e polystyrene f i l t e r h o l d e r c o n t a i n i n g the appropriate f i l t e r and a c e l l u l o s e support p a d . This device i s compatible with p e r s o n a l s a m p l i n g pumps a n d c a n b e a t t a c h e d t o a w o r k e r ' s c o l l a r o r l a p e l f o r t h e c o l l e c t i o n o f a b r e a t h i n g zone s a m p l e . A t t h e end o f t h e s a m p l i n g p e r i o d , t h e a i r f l o w r a t e and c o l l e c t i o n t i m e a r e r e c o r d e d t o c a l c u l a t e t h e t o t a l volume o f a i r sampled. T h i s samp l i n g p r o c e d u r e was u t i l i z e d i n t h e p r e s e n t s t u d y f o r t h e c o l l e c t i o n o f o r g a n o a r s e n i c a l p a r t i c u l a t e s g e n e r a t e d i n a dynamic a e r o s o l g e n e r a t i o n and s a m p l i n g s y s t e m . A n a l y t i c a l Procedure. The o p t i m i z e d a n a l y t i c a l p r o c e d u r e f o r d e t e r m i n a t i o n o f o r g a n o a r s e n i c a l s on t h e c o l l e c t e d f i l t e r samples i s as f o l l o w s .
In Chemical Hazards in the Workplace; Choudhary, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
24.
R i c c i ET AL.
Airborne
Organoarsenicals
385
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The o r g a n o a r s e n i c a l p a r t i c u l a t e s a r e e x t r a c t e d u l t r a s o n i c a l l y f r o m t h e f i l t e r s f o r 3 0 m i n u t e s i n 2 5 mL o f a n a q u e o u s c a r b o n a t e / bicarbonate/borate b u f f e r (Eluent 1, Table I ) . After sonication t h e r e s u l t i n g e x t r a c t s a r e r e a d y f o r a n a l y s i s a n d no f u r t h e r s a m p l e preparation is necessary. A s a m p l e i s i n j e c t e d o n t o a 3 x 5 0 0 mm a n i o n - e x c h a n g e s e p a r a t o r column and t h e o r g a n o a r s e n i c a l s a r e e l u t e d w i t h b u f f e r a t a f l o w r a t e o f 2 . 6 mL/min. The o r g a n o a r s e n i c a l s p e c i e s w h i c h a r e s e p a r a t e d a r e r e d u c e d t o t h e i r c o r r e s p o n d i n g a r s i n e d e r i v a t i v e s as t h e y e x i t the column i n the e l u e n t stream. T h i s i s achieved by m i x i n g t h e e l u e n t s t r e a m w i t h a s o l u t i o n o f 15% HC1 a c i d s a t u r a t e d w i t h p o t a s s i u m p e r s u l f a t e , and t h e n r e d u c i n g t h e a r s e n i c species w i t h 1% s o d i u m b o r o h y d r i d e ( N a B H ^ ) . The r e s p e c t i v e a r s i n e s o f t h e organoarsenicals are c a r r i e d to a heated quartz furnace (800°C) a l i g n e d i n t h e l i g h t p a t h o f t h e AAS where t h e r m a l d e c o m p o s i t i o n o f t h e a r s i n e d e r i v a t i v e s i n t o f r e e a r s e n i c atoms o c c u r s . The AAS i n s t r u m e n t a l p a r a m e t e r s a r e a d j u s t e d t o optimum f o l l o w i n g the m a n u f a c t u r e r ' s recommendations. A d e t a i l e d l i s t of instrumen t a l parameters f o r the t o t a l a n a l y t i c a l system i s g i v e n i n T a b l e I . Two s e p a r a t e a n a l y s e s o f a s a m p l e , u t i l i z i n g two e l u e n t b u f f e r systems o f d i f f e r e n t i o n i c s t r e n g t h , are r e q u i r e d f o r t h e complete c h a r a c t e r i z a t i o n o f a sample because A s ( i l l ) , i f p r e s e n t i n t h e sample, w i l l i n t e r f e r e w i t h t h e r e s o l u t i o n and d e t e r m i n a t i o n o f DMA. The two e l u e n t b u f f e r s w h i c h a r e u s e d a r e : E l u e n t 1 - 0.002^ M N a H C O / 0 . 0 0 1 9 M N a C 0 / 0 . 0 0 1 Μ ^ Β ^ Ο γ ; and E l u e n t 2 - 0 . 0 0 5 M Na2Bi 0j. 3
2
3
|
E l u e n t 1 a l l o w s t h e s e p a r a t i o n a n d d e t e r m i n a t i o n o f MMA, p - A P A , and A s ( V ) . I f A s ( l l l ) i s n o t p r e s e n t i n t h e s a m p l e , DMA i s a l s o e f f e c t i v e l y determined. The o r d e r o f e l u t i o n u s i n g E l u e n t 1 i s : u n r e s o l v e d D M A / A s ( l l l ) , MMA, p - A P A , a n d A s ( V ) . The e n t i r e chroma togram r e q u i r e s VL0 m i n u t e s and t h e a n a l y s i s c a n be p e r f o r m e d a t t h e r a t e o f 5 samples p e r h o u r . E l u e n t 2 i s a lower i o n i c s t r e n g t h b u f f e r and i s used o n l y t o r e s o l v e DMA f r o m i n t e r f e r i n g A s ( i l l ) . W i t h t h i s e l u e n t , MMA, p - A P A , and A s ( V ) have v e r y l o n g r e t e n t i o n t i m e s and w i l l accumulate on t h e column t y p i n g up a c t i v e r e s i n s i t e s . T h e r e f o r e t h e c o l u m n must b e f l u s h e d w i t h E l u e n t 1 a f t e r M . 0 - 1 5 samples have been a n a l y z e d and the column r e e q u i l i b r a t e d f o r 1 hour w i t h E l u e n t 2 b e f o r e f u r t h e r analysis. T h e a n a l y s i s o f DMA a n d A s ( i l l ) c a n b e p e r f o r m e d a t t h e r a t e o f 10 s a m p l e s p e r h o u r , a n d e a c h c h r o m a t o g r a m r e q u i r e s ^ 3 minutes. R e s u l t s and D i s c u s s i o n The c o n t r i b u t i o n o f v a p o r forms o f o r g a n o a r s e n i c a l s t o t h e t o t a l atmospheric c o n c e n t r a t i o n depends on t h e v a p o r p r e s s u r e o f e a c h compound a n d a l s o o n t h e t e m p e r a t u r e c o n d i t i o n s . D a t a on t h e v a p o r p r e s s u r e s o f t h e compounds s t u d i e d were n o t a v a i l a b l e a n d t h e r e f o r e t h e f o l l o w i n g e x p e r i m e n t was d e s i g n e d t o e s t i m a t e t h e c o n c e n t r a t i o n o f vapor forms found i n a w o r k p l a c e atmosphere.
In Chemical Hazards in the Workplace; Choudhary, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
CHEMICAL HAZARDS IN THE WORKPLACE
386
Table I.
Instrumental
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organoarsenicals
Ion Chromatograph
conditions
f o r the analysis
i n a i r particulate
of
samples
Parameters
Column M o b i l e Phase Flow Rate Eluent 1
D i o n e x 3x500 mm A n i o n - E x c h a n g e 2 . 6 mL/min
Eluent 2 Injection
0.005 M Na B^0j Variable
0.0021* M ïïaHCO / 0 . 0 0 1 9 M N a C 0 0.001 M Na^ÇOy 2
2
Loop
Arsine Generation 1 5 $ HC1 w / s a t u r a t e d persulfate 1% N a B H ^ / 0 . 2 ^ Κ0Η A r g o n C a r r i e r Gas
Parameters potassium 0 . 8 mL/min 2 . 0 mL/min 300 ce/min
AAS P a r a m e t e r s A r s e n i c EDL Wavelength S l i t Width Quartz Furnace D Background C o r r e c t i o n Signal Scale Expansion Recorder C h a r t Speed 2
8 watts 1 9 3 . 7 nm 0 . 7 nm 800°C None Absorbance 3x 1 0 mv f u l l 1 cm/min
scale
In Chemical Hazards in the Workplace; Choudhary, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.
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RICCI E T
AL.
Airborne
Organoarsenicals
387
An enclosed sampling t r a i n f o r g e n e r a t i o n and q u a n t i t a t i v e c o l l e c t i o n o f vapors was assembled w i t h the f o l l o w i n g components: ( l ) a g l a s s impinger wrapped w i t h h e a t i n g tape t o serve as a vapor generator and m o d i f i e d so t h a t the a i r i n l e t tube was Ά cm above the bottom; (2) a k'Jmm c e l l u l o s e e s t e r membrane f i l t e r i n - l i n e t o c o l l e c t p a r t i c u l a t e s ; (3) t h r e e bubblers i n s e r i e s t o c o l l e c t any vapors, each c o n t a i n i n g 15.0 mL o f 0.1 Ν NaOH; and (k) a vacuum pump. MMA, DMA, and p-APA were p l a c e d i n t h e heated impinger which was maintained at a temperature o f 50°C (l22°F) t o simulate an extreme sampling temperature s i t u a t i o n . A i r , at t h e r a t e o f 0.2 l i t e r s / m i n , was drawn over the heated s a l t s and through the f i l t e r and the t h r e e b u b b l e r s . Two sampling experiments were performed: i n the f i r s t , a t o t a l volume o f 30 l i t e r s of a i r was sampled i n 2.5 hours; i n the second, a t o t a l volume o f 100 l i t e r s o f a i r was sampled i n 8.0 hours. A f t e r sampling, each bubbler was a c i d i f i e d by adding 10.0 mL o f 10$ HNO^ a c i d s a t u r a t e d w i t h potassium p e r s u l f a t e . The bubbler samples were then analyzed f o r t o t a l a r s e n i c u s i n g the automated h y d r i d e g e n e r a t i o n system of V i j a n and Wood (12). The r e s u l t s f o r both experiments showed t h a t the extent t o which any o r g a n o a r s e n i c a l vapors may have been generated under these c o n d i t i o n s was immeasurable and below the a n a l y t i c a l detec t i o n l i m i t ( i . e .
