A New Fluorescence Procedure for the Determination of Methyl

7 A N e w Fluorescence Procedure for the Determination of Methyl Isocyanate in the Occupational Environment W. J. VINCENT and N. H . K E T C H A M

Downloaded by UNIV OF ARIZONA on January 13, 2013 | http://pubs.acs.org Publication Date: April 22, 1980 | doi: 10.1021/bk-1980-0120.ch007

Union Carbide Corporation, Chemicals and Plastics, Research and Development Department, P.O. Box 8361, South Charleston, WV 25303

M e t h y l i s o c y a n a t e and a l l i s o c y a n i c a c i d e s t e r s a r e an i n t e r e s t i n g and h i g h l y r e a c t i v e c l a s s o f o r g a n i c compounds, s i n c e t h e i s o c y a n a t e g r o u p (-NC0) r e a c t s r e a d i l y w i t h a w i d e v a r i e t y o f compounds a s w e l l as w i t h i t s e l f t o f o r m d i m e r s , t r i m e r s , u r e a s , and c a r b o d i - i m i d e s . M e t h y l i s o c y a n a t e (MIC) i s an i n t e r m e d i a t e i n t h e p r e p a r a t i o n o f c a r b a m a t e p e s t i c i d e s a n d c o n c e i v a b l y c o u l d be a p p l i e d t o t h e p r o d u c t i o n o f s p e c i a l h e t e r o c y c l i c p o l y m e r s and d e r i v a t i v e s . M e t h y l i s o c y a n a t e i s a h a z a r d o u s c h e m i c a l b y a l l means o f c o n t a c t . I n h a l a t i o n o f t h e m a t e r i a l can r e s u l t i n s e v e r e b r o n c h o s p a s m s and a s t h m a t i c b r e a t h i n g . B e c a u s e o f i t s h i g h vapor p r e s s u r e , the p o s s i b i l i t i e s o f i n h a l a t i o n are g r e a t l y e n h a n c e d . T h e t h r e s h o l d l i m i t v a l u e (TLV) i s a 0.02 p a r t s p e r m i l l i o n time weighted average ( 1 ) . A s e a r c h o f t h e l i t e r a t u r e i n d i c a t e d t h a t s e v e r a l methods f o r d e t e r m i n i n g MIC i n a i r have been d e v e l o p e d . T h e s e methods i n v o l v e t h e use o f ( a ) s i l i c a gçl i m p r e g n a t e d w i t h p - a m i n o a z o b e n z e n e (b) two m i d g e t i m p i n g e r s i n s e r i e s c o n t a i n i n g a d i m e t h y l s u l f o x i d e - h y d r o c h l o r i c a c i d absorber s o l u t i o n and r e a c t i o n w i t h 1 - f l u o r o - 2 , 4 - d i n i t r o b e n z e n e ( c ) and c o l l e c t i o n on an a d s o r b e n t , t h e r m a l d e s o r p t i o n , and s u b s e q u e n t r e a c t i o n 1 - f l u o r o - 2 , 4 - d i n i t r o b e n z e n e ( 2 ) . These a i r s a m p l i n g and a n a l y t i c a l p r o c e d u r e s have a v a r i e t y o f s h o r t c o m i n g s . They a r e i n c o n v e n i e n t and cumbersome, a n d l a c k t h e n e c e s s a r y s e n s i t i v i t y and s p e c i f i c i t y t o d e t e r m i n e m e t h y l i s o c y a n a t e a c c u r a t e l y f o r an e i g h t hour t i m e w e i g h t e d a v e r a g e as r e q u i r e d u n d e r t h e O c c u p a t i o n a l S a f e t y A c t o f 1970. T h e a n a l y t i c a l p h a s e o f t h e s e p r o c e d u r e s a r e t i m e c o n s u m i n g and a r e v e r y d i f f i c u l t t o use i n d e t e r m i n i n g p e r s o n n e l e x p o s u r e t o MIC i n t h e i n d u s t r i a l environment. Scope o f t h e D e v e l o p m e n t Work The s c o p e o f t h e work i n c l u d e s t h e s t e p s t a k e n t o w a r d s t h e d e v e l o p m e n t o f a sound a i r s a m p l i n g and a n a l y t i c a l method f o r 0-8412-0539-6/80/47-120-121$06.75/0 © 1980 American Chemical Society In Analytical Techniques in Occupational Health Chemistry; Dollberg, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

OCCUPATIONAL H E A L T H CHEMISTRY

122


d e t e r m i n i n g MIC i n a i r . T h e s e s t e p s i n c l u d e d t h e d e v e l o p m e n t and e v a l u a t i o n o f two f l u o r o g e n i c a s s a y p r o c e d u r e s . The e a r l y work u s e d s i l i c a g e l as t h e s o l i d a d s o r b e n t f o r s a m p l i n g . L a t e r i t was f o u n d t h a t A m b e r l i t e XAD-2 i o n e x c h a n g e r e s i n made i t p o s s i b l e t o s i g n i f i c a n t l y improve the s e n s i t i v i t y of the method. The d e v e l o p m e n t work d e s c r i b e d i n t h i s r e p o r t i s g i v e n i n t h e c h r o n o l o g i c a l o r d e r i n w h i c h i t was p e r f o r m e d i n o r d e r t o show t h e s e q u e n c e o f t h e e x p e r i m e n t a l work. The XAD-2 p r o c e d u r e w i l l be t h e p r e f e r r e d method f o r most i n d u s t r i a l h y g i e n e u s e s . I n f o r m a t i o n a b o u t c o l l e c t i o n on s i l i c a g e l i s i n c l u d e d as t h i s m i g h t be t h e p r e f e r r e d a d s o r b e n t i n some c a s e s . Search f o r a S u i t a b l e A n a l y t i c a l

Procedure

I n i t i a l l y , a n a l y t i c a l f e a s i b i l i t y s t u d i e s were c o n d u c t e d t o d e t e r m i n e i f m e t h y l i s o c y a n a t e c o u l d be r e c o v e r e d q u a n t i t a t i v e l y f r o m a d s o r b e n t s and a n a l y z e d by any means o f a n a l y s i s . Gas c h r o m a t o g r a p h i c , s p e c t r o p h o t o m e t r y , g r a v i m e t r i c , and c o l o r m e t r i c a n a l y t i c a l methods were i n v e s t i g a t e d b u t a l l p o s s e s s e d i n a d e q u a c i e s t h a t l e d t o t h e i r d i s q u a l i f i c a t i o n as a method o f a n a l y s i s f o r MIC. D u r i n g t h e s e t e s t s , i t was d i s c o v e r e d t h a t s i l i c a g e l , A m b e r l i t e XAD-2 i o n e x c h a n g e r e s i n , and C o l u m b i a JXC c a r b o n r e t a i n e d the i s o c y a n a t e e f f i c i e n t l y , but d i d not r e l e a s e the compound a t a l l o r were n o t r e l e a s i n g t h e compound i n a f o r m t h a t c o u l d be a n a l y z e d . S i n c e i s o c y a n a t e s r e a c t w i t h w a t e r o f o r d i n a r y t e m p e r a t u r e s t o g i v e d i s u b s t i t u t e d u r e a s and c a r b o n d i o x i d e , a n a l y t i c a l methods f o r u r e a s were i n v e s t i g a t e d as a means o f a n a l y s i s . I t was d i s c o v e r e d t h a t t h e r e a c t i o n p r o d u c t o f u r e a and d i a c e t y l m o n o x i m e when h e a t e d i n t h e p r e s e n c e o f s u l f u r i c a c i d f l u o r o s c e n c e s a t a w a v e l e n g t h o f 415 mu a t an a c t i v a t i o n w a v e l e n g t h o f 380 mu ( 3 ) . S i n c e f l u o r e s c e n c e methods a r e u s u a l l y q u i t e s e n s i t i v e , t h i s a p p r o a c h was i n v e s t i g a t e d as means o f d e t e r m i n i n g MIC i n a i r a t t h e TLV. The d i a c e t y l m o n o x i m e method was e v a l u a t e d by p l a c i n g known c o n c e n t r a t i o n s o f MIC on t h e c a n d i d a t e a b s o r b e n t s , a s p i r a t i n g l a b o r a t o r y a i r t h r o u g h t h e a d s o r b e n t s t o f a c i l i t a t e any r e a c t i o n t h a t m i g h t o c c u r , d e s o r b i n g and r e a c t i n g w i t h d i a c e t y l m o n o x i m e t o p r o d u c e f l u o r o p h o r s , and d e t e r m i n i n g t h e f l u o r e s c e n c e on a s p e c t r o f l u o r o m e t e r . T a b l e I shows t h e amount of f l u o r e s c e n c e o b t a i n e d f r o m s e v e r a l a d s o r b e n t s u s i n g t h e d i a c e t y l m o n o x i m e method. T h e s e r e s u l t s i n d i c a t e d t h a t s i l i c a g e l and A m b e r l i t e i o n e x c h a n g e r e s i n were t h e b e s t a d s o r p t i o n / d e s o r p t i o n mediums u n d e r t h e s e c o n d i t i o n s . S i n c e s i l i c a g e l had t h e h i g h e s t f l u o r o e s c e n c e , i t was s e l e c t e d as t h e p r i m a r y s o l i d a d s o r b e n t f o r MIC.

In Analytical Techniques in Occupational Health Chemistry; Dollberg, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

7. VINCENT AND K E T C H A M

Determination

of Methyl

Isocyanate


TABLE I R e l a t i v e F l u o r e s c e n c e O b t a i n e d From V a r i o u s A d s o r b e n t s U s i n g The D i a c e t y l m o n o x i m e P r o c e d u r e

Adsorption Medium

S i l i c a G e l , GC G r a d e 20/40 mesh

Amount o f MIC P l a c e d o n A d o s r b e n t , ug

Percent Transmittance

925

51

1850

40

P o r a p a k N, 50/80 mesh

925

0

P o r a p a k T, 50/80 mesh

925

0

A m b e r l i t e XAD-2

925

30

1* H P 0 Gel

4

Silica


123


124


B e c a u s e MIC i s t h o u g h t t o r e a c t w i t h w a t e r t o f o r m d i m e t h y l u r e a (DMU), s t a n d a r d s o l u t i o n s o f DMU were p r e p a r e d and a n a l y z e d u s i n g t h e d i a c e t y l m o n o x i m e method. The p u r p o s e was t o d e t e r m i n e w h e t h e r o r n o t DMU c o u l d be u s e d t o make s t a n d a r d s w h i c h were r e p r e s e n t a t i v e o f t h e b e h a v i o r o f MIC o n t h e a d s o r b e n t and i n a i r . The r e s u l t s i n d i c a t e d t h a t t h e u r e a may n o t be p r o d u c e d o n s i l i c a g e l o r t h a t t h e r e a c t i o n s were n o t s t o i c h i o m e t r i c , b e c a u s e more f l u o r e s c e n c e was o b t a i n e d f r o m MIC s t a n d a r d s t h a n u r e a . Good r e c o v e r i e s were o b t a i n e d when t h e r e s u l t s were compared w i t h MIC s t a n d a r d s . B e c a u s e o f t h e l i m i t e d range of the s p e c t r o f l u o r o m e t e r f o r q u a n t i t a t i v e a n a l y s i s , h i g h p e r f o r m a n c e l i q u i d c h r o m a t o g r a p h y (HPLC) w i t h f l u o r e s c e n c e d e t e c t i o n was i n v e s t i g a t e d as a method o f a n a l y s i s f o r MIC and d i a c e t y l m o n o x i m e . S e v e r a l u n s u c c e s s f u l a t t e m p t s were made t o a n a l y z e t h e f l u o r o p h o r p r o d u c e d by t h e r e a c t i o n o f MIC w i t h d i a c e t y l monoxime u s i n g HPLC and a m u l t i w a v e l e n g t h f l u o r o e s c e n c e d e t e c t o r . Because o f a s e r i e s of a n a l y t i c a l problems, a search was i n i t i a t e d f o r a method t h a t w o u l d l e n d i t s e l f t o l i q u i d c h r o m a t o g r a p h i c a n a l y s i s more r e a d i l y . S i n c e m e t h y l i s o c y a n a t e probably r e a c t s with water according t o the f o l l o w i n g equation: -C0 CH3NCO + H 0 — > 2

CH3NHCOOH

2

>

CH3NH2

CH3NCO >

CH3NHCONHCH3,

t o p r o d u c e monomethylamine as an i n t e r m e d i a t e p r o d u c t , a h i g h l y s e n s i t i v e f l u o r e s c e n t p r o c e d u r e was i n v e s t i g a t e d as a means o f d e t e r m i n i n g MIC i n a i r . Reaction of Fluorescamine

w i t h MIC

A s e a r c h o f t h e l i t e r a t u r e r e v e a l e d t h a t t h e r e were s e v e r a l s e n s i t i v e a s s a y p r o c e d u r e s f o r p r i m a r y a m i n e s , b u t none o f these procedures possessed t h e c a p a b i l i t i e s of determining c o n c e n t r a t i o n i n t h e p i c o m o l e r a n g e . The l i t e r a t u r e s e a r c h d i d r e v e a l t h a t f l u o r e s c a m i n e (Fluram) r e a c t s w i t h a l i p h a t i c amines t o p r o d u c e i n t e n s e f l u o r o p h o r s t h a t c a n be d e t e c t e d i n t h e p i c o m o l e r a n g e . Known q u a n t i t i e s o f t h e o r g a n o i s o c y a n a t e were p l a c e d o n s i l i c a g e l t u b e s . Lab a i r was a s p i r a t i n g t h r o u g h t h e t u b e s , and r e a c t i n g w i t h F l u r a m . I t was d i s c o v e r e d t h a t f l u o r e s c a m i n e r e a c t e d w i t h MIC o n s i l i c a g e l t o p r o d u c e h i g h l y f l u o r e s c e n t p r o d u c t s a t m i c r o g r a m c o n c e n t r a t i o n s ( > TOO). These f l u o r o s c e n t products e m i t t e d a g r e a t e r f l u o r e s c e n c e than t h e d i a c e t y l m o n o x i m e f l u o r o p h o r s and were f o u n d t o be e a s y t o a n a l y z e and q u i t e s t a b l e compounds. F l u r a m i n t e t r a h y d r o f u r a n i s n o n f l u o r o e s c e n t and t h e r e a c t i o n w i t h p r i m a r y amines i s s t a t e d t o be p r o p o r t i o n a l t o t h e a c t u a l amine c o n t e n t . This p r o c e d u r e was f u r t h e r e v a l u a t e d by p l a c i n g known q u a n t i t i e s o f



Determination

of Methyl

Isocyanate

125

MIC i n f l e x i b l e b a g s , e v a c u a t i n g t h e c o n t e n t o f t h e bag t h r o u g h s i l i c a g e l , d e s o r b i n g w i t h F l u r a m s o l u t i o n , and a n a l y z i n g by HPLC u s i n g a m u l t i w a v e l e n g t h f l u o r e s c e n t d e t e c t o r . T a b l e I I i l l u s t r a t e s t h e r e c o v e r i e s o f MIC t h a t were o b t a i n e d a t s e v e r a l c o n c e n t r a t i o n s . S t a t i s t i c a l a n a l y s i s o f the r e s u l t s revealed t h a t t h e a c c u r a c y and t h e p r e c i s i o n o f t h e method w i t h i n t h e r a n g e o f 41 t o 2 ppm was 4.9% and 4.4% r e s p e c t i v e l y . S t a n d a r d s were p r e p a r e d b y a p p l y i n g i d e n t i c a l c o n c e n t r a t i o n s o n s i l i c a gel and a n a l y z i n g i n t h e same way a s t h e s a m p l e t u b e s .


Chemistry of the Fluram-MIC R e a c t i o n Fluorescamine i s 4-phenylspiro[furan-2(3H),1-phthalanJ 3 , 3 ' d i o n e . MIC s h o u l d r e a c t w i t h f l u r a m a c c o r d i n g t o t h e following equation:

T h i s r e a c t i o n t a k e s p l a c e i n a m a t t e r o f s e c o n d s and p r o d u c e s s i g n i f i c a n t l y more f l u o r e s c e n c e t h a n t h e diacetylmonoxime f l u o r o p h o r s . Excess reagent i s q u i c k l y hydrolyzed to form nonfluorescent water s o l u b l e products. Secondary, t e r t i a r y , and a r o m a t i c amines d i d n o t r e a c t w i t h f l u r a m t o p r o d u c e any m e a s u r e a b l e f l u o r e s c e n c e . T h e r e a c t i o n d i d n o t o c c u r when ammonia and ammonium s a l t s were t e s t e d f o r f l u o r e s c e n c e . Mass s p e c t r o m e t r y o f an a c t u a l f i e l d s a m p l e c o n f i r m e d t h a t t h e s u b s t i t u t i o n p r o d u c t i s t h e f l u o r e s c e n t s p e c i e s t h a t i s shown above. F u r t h e r mass s p e c t r a s t u d i e s i n d i c a t e d t h a t d i m e t h y l u r e a i s n o t p r o d u c e d d u r i n g t h i s r e a c t i o n . T h i s was l a t e r c o n f i r m e d by i n t r o d u c i n g known q u a n t i t i e s o f t h e u r e a and l i t t l e o r no f l u o r e s c e n c e was n o t e d . T h e s e t e s t s i n d i c a t e t h a t F l u r a m does r e a c t w i t h t h e p r i m a r y amine i n t e r m e d i a t e on t h e a d s o r b e n t a c c o r d i n g t o t h e above e q u a t i o n , and t h a t m o n o m e t h y l a m i n e and o t h e r p r i m a r y a l i p h a t i c amines w o u l d interfere.



126

TABLE I I


R e c o v e r y Of MIC From F l e x i b l e Bags On S i l i c a G e l

Expected C o n c e n t r a t i o n , ppm

Recovered C o n c e n t r a t i o n , ppm

40.8 40.8 40.8 40.8 40.8 20.4 20.4 20.4 20.4 20.4 4.1 4.1 4.1 4.1 4.1 2.04 2.04 2.04 2.04 2.04

43.2 34.6 33.7 41.2 52.4 16.5 16.8 21.3 18.1 20.0 4.4 3.8 3.8 3.5 4.0 1.98 1.76 1.84 2.21 1.98 Total X Recovery S A Ρ

% Recovery

106 85 83 101 128 81 83 104 89 98 107 93 93 85 98 97 86 90 108 97

=95.6 = 3.9 = 4.4% = 4.0



Determination

of Methyl

Isocyanate

E v a l u a t i o n o f t h e L i q u i d C h r o m a t o g r a p h i c Columns Several high performance l i q u i d chromatographic columns were e v a l u a t e d a c c o r d i n g t o t h e i r c a p a b i l i t i e s t o s e p a r a t e and r e l e a s e the MIC-Fluram f l u o r o p h o r . Reverse phase, normal p a r t i t i o n , and amine bonded c o l u m n s w e r e t e s t e d . T h e r e v e r s e p h a s e c o l u m n s p e r f o r m e d t h e s e p a r a t i o n and a n a l y s i s more p r o f i c i e n t l y t h a n t h e o t h e r c o l u m n s . A V a r i a n CH-10 c o l u m n was t h e b e s t c o l u m n f r o m among t h e s e v e r a l o n e s t h a t were t e s t e d .


L i m i t o f D e t e c t i o n and

Sensitivity

The l i m i t o f d e t e c t i o n o f t h e s i l i c a g e l a d s o r p t i o n / d e s o r p t i o n p r o c e d u r e was d e t e r m i n e d b y p l a c i n g known c o n c e n t r a t i o n s on the adsorbent, p u l l i n g l a b a i r through the a d s o r b e n t a t 500 c c p e r m i n u t e f o r 15 m i n u t e s , and a n a l y z i n g u s i n g t h e f l u o r o g e n i c a s s a y method. F i g u r e 1 i l l u s t r a t e s a t y p i c a l c a l i b r a t i o n c u r v e t h a t can be o b t a i n e d u s i n g t h e procedure. The l i m i t o f d e t e c t i o n w i t h l i n e a r i t y was d e t e r m i n e d t o be 4.76 m i c r o g r a m s p e r m i l l i l i t e r w h i c h i s t o 0.02 ppm i n a 180 l i t e r a i r s a m p l e ( 6 h r ) . H u m i d i t y E f f e c t s Upon Sample R e t e n t i o n The e f f e c t s o f m o i s t u r e upon s a m p l e r e t e n t i o n were e v a l u a t e d by a s p i r a t i n g m o i s t a i r at 90% r e l a t i v e h u m i d i t y t h r o u g h a d s o r p t i o n t u b e s c o n t a i n i n g known c o n c e n t r a t i o n s o f MIC. T h e s a m p l e s were a n a l y z e d i n t h e u s u a l manner. No s i g n i f i c a n t e f f e c t s o f m o i s t u r e upon s a m p l e r e t e n t i o n were noted. Table I I I c o n t a i n s the p e r t i n e n t s t a t i s t i c a l data which was o b t a i n e d d u r i n g t h e h u m i d i t y e f f e c t s e v a l u a t i o n . Elimination o f Interferences S i n c e e a r l i e r s t u d i e s r e v e a l e d t h a t monomethylamine w o u l d i n t e r f e r e , f u r t h e r s t u d i e s were conducted t o determine i f the r e m o v a l o f t h i s i n t e r f e r e n c e c o u l d be a c c o m p l i s h e d . A brief l i t e r a t u r e s u r v e y r e v e a l e d t h a t an aqueous s o l u t i o n o f c u p r i c c h l o r i d e c o u l d c o n c e i v a b l y remove a l l amine i n t e r f e r e n c e s . S i n c e t h e s o l u b i l i t y o f m e t h y l i s o c y a n a t e i s o n l y 6.7% by w e i g h t i n w a t e r , i t was t h o u g h t t h a t t h e o r g a n i c i s o c y a n a t e w o u l d p o s s i b l y p a s s t h r o u g h aqueous m e d i a u n m o d i f i e d ; and t h u s a l l o w t h e q u a n t i t a t i v e d e t e r m i n a t i o n o f MIC i n t h e p r e s e n c e o f i n t e r f e r e n c e s w h i c h w o u l d be removed i n aqueous s o l u t i o n s . T h e e f f e c t i v e n e s s o f t h e r e m o v a l o f t h e i n t e r f e r e n c e o f monom e t h y l a m i n e was d e t e r m i n e d b y g e n e r a t i n g known c o n c e n t r a t i o n s o f MIC and monomethylamine i n a i r and s a m p l i n g t h r o u g h an i m p i n g e r c o n t a i n i n g 0.5% c u p r i c c h l o r i d e w h i c h was f o l l o w e d b y


128


140

130

120 110 100 90 H

i g

8

0

70

60


50

40

30

20

10

10

20

30

40

50

60

70

80

90

100

ΪΤθ

120

MICROGRAMS

Figure 1.

Typical calibration curve obtained from silica gel

TABLE I I I E f f e c t s o f H u m i d i t y Upon Sample R e t e n t i o n On S i l i c a G e l

Expected ppm

Recovered ppm

% Relative Humidity

20.4

20.7

92

101.5

20.4

20.6

92

100.9

20.4

19.2

92

94.1

20.4

20.6

92

100.9

20.4

20.8

92

101.8

X = 20.38 ppm S = 0.66 ppm

Percent Recovery

CV = 3 . 2 % A = 0.09%




Determination

of Methyl

Isocyanate

129

an a d s o r p t i o n t u b e c o n t a i n i n g s i l i c a g e l . The d a t a t h a t i s shown i n T a b l e I V l i s t s t h e amounts o f MIC t h a t were r e c o v e r e d i n t h e p r e s e n c e o f 100 ppm o f m o n o m e t h y l a m i n e . T h e s e r e s u l t s i n d i c a t e t h a t MMA w i l l n o t i n t e r f e r e w i t h t h e d e t e r m i n a t i o n o f MIC even a t c o n c e n t r a t i o n s w h i c h a p p r o a c h 100 ppm. To f u r t h e r evaluate the c a p a b i l i t i e s o f the l i q u i d scrubber/solid a d s o r p t i o n t e c h n i q u e , a known c o n c e n t r a t i o n o f MIC was p u l l e d t h r o u g h t h e s a m p l i n g s y s t e m and a n a l y z e d b y t h e f l u o r o g e n i c assay procedure. The r e s u l t s shown i n T a b l e V i n d i c a t e t h a t 98.6% o f t h e e x p e c t e d MIC c o n c e n t r a t i o n was r e c o v e r e d t h r o u g h t h e C u C l ? s o l u t i o n . These e x p e r i m e n t s i n d i c a t e d t h a t t h e C u C l 2 p r e f i l t e r i s a v e r y e f f e c t i v e means o f r e m o v i n g t h e i n t e r f e r e n c e o f m o n o m e t h y l a m i n e and o t h e r amines w h i l e a l l o w i n g t h e q u a n t i t a t i v e p a s s a g e o f MIC. F i e l d E v a l u a t i o n o f t h e Method The method was e v a l u a t e d i n t h e f i e l d i n o r d e r t o d e t e r m i n e i f ( a ) t h e a d s o r p t i o n medium f u n c t i o n e d p r o p e r l y i n t h e o c c u p a t i o n a l s e t t i n g , ( b ) i f any sample d i s p l a c e m e n t o c c u r r e d , and ( c ) i f t h e r e m i g h t be a n y a d d i t i o n a l i n t e r f e r e n c e s . In o r d e r t o d e t e r m i n e i f t h e method f u n c t i o n e d p r o p e r l y i n t h e o c c u p a t i o n a l e n v i r o n m e n t , s i m u l t a n e o u s s a m p l e s were t a k e n u s i n g i m p i n g e r s c o n t a i n i n g t h e c u p r i c c h l o r i d e p r e f i l t e r and s i l i c a g e l t u b e s w i t h o u t a p r e f i l t e r . T h e s e s a m p l e s were c o l l e c t e d s i d e b y s i d e and u n d e r t h e same c o n d i t i o n s i n i n d u s t r i a l e n v i r o n m e n t s w h e r e MIC was n o t l i k e l y t o be p r e s e n t . I f there were any a m b i e n t i n t e r f e r e n c e s , t h e r e w o u l d be s i g n i f i c a n t d i f f e r e n c e s i n t h e c o n c e n t r a t i o n s t h a t were o b t a i n e d by t h e c o l l e c t i o n p r o c e d u r e s . Table VI i l l u s t r a t e s t h e r e s u l t s t h a t were o b t a i n e d and no s i g n i f i c a n t d i f f e r e n c e s i n t h e c o n c e n t r a t i o n s c o u l d be d e t e r m i n e d . A i r s a m p l e s were a l s o c o l l e c t e d i n i n d u s t r i a l a t m o s p h e r e s that contained the organoisocyanate. Table VII contains the r e s u l t s t h a t were o b t a i n e d and i n d i c a t e t h e p r o c e d u r e i s c a p a b l e o f m e a s u r i n g MIC i n o c c u p a t i o n a l environments. A m b e r l i t e XAD-2 R e s i n

Procedure

S i n c e a 6 h o u r s a m p l i n g t i m e was n e c e s s a r y i n o r d e r t o determine t h e t h r e s h o l d l i m i t value using the s i l i c a g e l p r o c e d u r e , A m b e r l i t e XAD-2 s y n t h e t i c i o n e x c h a n g e r e s i n was a g a i n t e s t e d a s an a d s o r p t i o n medium, t h i s t i m e u s i n g t h e fluorescamine a n a l y t i c a l procedure. Laboratory t e s t s revealed t h a t XAD-2 r e l e a s e d t h e M I C - f l u r a m f l u o r o p h o r more e f f i c i e n t l y a t l o w e r c o n c e n t r a t i o n s t h a n s i l i c a g e l . F i g u r e s 2 and 3 i l l u s t r a t e t h e c h r o m a t o g r a p h i c r e s p o n s e and t h e l i n e a r i t y o f the procedure. U s i n g XAD-2, 238 nanograms o f MIC c o u l d be


130


TABLE IV


R e c o v e r y o f MIC I n The P r e s e n c e Of M o n o e t h y l a m i n e on S i l i c a G e l Expected Amount, ppm

Recovered Amount, ppm

Percent Recovery

20.4

18.2

89.2

20.4

16.7

82.0

20.4

16.7

82.0

20.4

19.3

94.6

20.4

17.1

83.6 A c c u r a c y = 11 -456 P r e c i s i o n = 9 . 2556

X = 88.6 S = 8.2

TABLE V R e c o v e r y Of MIC T h r o u g h 0.556 C u C l 2 S o l u t i o n Expected Amount, ppm

Recovered Amount, ppm

Percent Recovery

20.4

17.4

85.3

20.4

20.0

98.1

20.4

21.1

103.4

20.4

20.2

99.0

20.4

21.9

107.0

X = 98.6 S = 8.256

A c c u r a c y = 1.456 P r e c i s i o n = 8.32



Determination

of Methyl

Isocyanate

131

TABLE V I R e s u l t s O f S i m u l t a n e o u s S a m p l e s C o l l e c t e d W i t h and Without CuCl2 F i l t e r In I n d u s t r i a l Environments


Sample No. & Type

Concentration,

ppm

T o t a l Volume, l i t e r s

ΙΑ-Nonfiltered IB-Filtered 2A-Nonfiltered 2B-Filtered 3A-Nonfiltered 3B-Filtered

il s a m p l e l o o p Retention

time 1.0 m i n u t e s

4.

APPARATUS AND REAGENTS Chroma-Vue Model CC-20 UV Box; U l t r a - v i o l e t P r o d u c t s , I n c . , San G a b r i e l , CA. F l u o r e s c a m i n e ( F l u r a m ) , P i e r c e C h e m i c a l Company, Box 117, R o c k f o r d , I L 61105. c) M e t h y l I s o c y a n a t e , 9 9 % minimum d) T e t r a h y d r o f u r a n , non s p e c t r o - d i s t i l l e d i n g l a s s , B u r d i c k and J a c k s o n , Muskegan, MI 4 9 4 4 2 . e) S c r e w - c a p v i a l s w i t h s e p t u m s , P i e r c e C h e m i c a l Company. f ) P e r s o n a l s a m p l i n g pumps, S i p i n Model Sp-2 o r e q u i v a l e n t . P u r i f i e d XAD-2 r e s i n , A p p l i e d S c i e n c e L a b o r a t o r i e s , I n c . , S t a t e C o l l e g e , PA 16801. F i r e p o l i s h e d g l a s s t u b e s , 8 mm O.D. χ 6 mm I.D. b y 15 cm l e n g t h , i) Si lane-treated glass wool, j ) End c a p s , A l t e c h A s s o c i a t e s , S t . No. 4 0 2 5 . k) S t o p w a t c h . 1) Soap f i l m f l o w m e t e r . m) S y r i n g e , 1 ml s o l v e n t f l u s h i n g s y r i n g e ; A l t e c h Associates, Inc., Arlington Heights, IL. S y r i n g e , 5 0 - m i c r o l i t e r Glenco sample s y r i n g e , A l t e c h Associates, Inc. o) S y r i n g e , 1 0 - m i c r o l i t e r H a m i l t o n , p) M e t h a n o l , C = 0 - f r e e . q) C u p r i c c h l o r i d e d i h y d r a t e . r ) Sodium c a r b o n a t e , s) E t h y l e t h e r . t ) Funnel, Buchner, w i t h coarse f r i t t e d d i s c , u) Vacuum f l a s k , 5 0 0 - m l .



5.

b) c)


d) e) f)

Isocyanate

Weigh 25 g o f XAD-2 r e s i n i n t o a B u c h n e r f u n n e l w i t h fritted disc. Wash t w i c e w i t h 50 ml o f m e t h a n o l , u s i n g vacuum t o p u l l excess methanol from r e s i n . Wash t w i c e w i t h 50 ml o f d i s t i l l e d w a t e r , u s i n g vacuum to p u l l excess water from r e s i n . A d d l g o f s o d i u m c a r b o n a t e t o 100 ml o f d i s t i l l e d w a t e r . Wash r e s i n w i t h s o d i u m c a r b o n a t e s o l u t i o n and p u l l e x c e s s f r o m r e s i n w i t h vacuum. R i n s e t w i c e w i t h 50 ml o f e t h y l e t h e r and a l l o w t o d r y a t room t e m p e r a t u r e .

PREPARATION OF FLUORESCAMINE AND CUPRIC CHLORIDE SOLUTIONS a)

b)

c) d) e) f)

7.

of Methyl

PREPARATION OF ION EXCHANGE XAD-2 RESIN a)

6.

Determination

F l u r a m Weigh 0.35 g o f f l u o r e s c a m i n e t o t h e n e a r e s t 0.1 mg and p l a c e i n a 100-ml v o l u m e t r i c f l a s k . Add t e t r a h y d r o f u r a n and s w i r l . D i l u t e t o t h e mark w i t h additional tetrahydrofuran. P i p e t 10 ml o f t h i s s o l u t i o n i n t o a n o t h e r 100-ml v o l u m e t r i c and d i l u t e t o t h e mark w i t h t e t r a h y d r o f u r a n . T h i s s o l u t i o n i s used f o r d e s o r p t i o n o f t h e MIC f r o m the adsorbent. S t o r e i n r e f r i g e r a t o r u n t i l needed. CuCIo S o l u t i o n Weigh 5 g o f C u C l ? and p l a c e i n t o a 1 - l i t e r v o l u m e t r i c f l a s k and d i l u t e t o t h e mark w i t h d i s t i l l e d water. P l a c e 2 ml o f t h i s s o l u t i o n i n t o a m i c r o - i m p i n g e r and attach the e x i t port to the primary section o f the a d s o r p t i o n t u b e s b y means o f a 5.0-cm p i e c e o f t u b i n g . The c u p r i c c h l o r i d e p r e f i l t e r i s e s s e n t i a l t o t h e d e t e r m i n a t i o n i f monomethylamine and MIC a r e known t o e x i s t i n t h e same e n v i r o n m e n t .

PREPARATION OF ADSORPTION TUBES a) b) c) d)

Cut 8-mm O.D. (6 mm - I.D.) P y r e x g l a s s t u b i n g i n t o 15.0-cm l e n g t h s and f i r e p o l i s h t h e e n d s . Introduce a s i l a n e - t r e a t e d g l a s s wool p l u g a p p r o x i m a t e l y 8 0 mm f r o m t h e o p e n i n g . Add washed XAD-2 r e s i n i n l e n g t h s o f 70 mm f o r t h e p r i m a r y s e c t i o n and 30 mm f o r t h e backup s e c t i o n . A d d g l a s s wool p l u g s t o t h e e x i t and e n t r a n c e s e c t i o n s o f t h e t u b e and cap w i t h t h e end c a p s u n t i l r e a d y f o r use.


146

8.


SAMPLING PROCEDURE a) b) c) d)


e) 9.

I m m e d i a t e l y b e f o r e s a m p l i n g , remove t h e end c a p s f r o m the a d s o r p t i o n t u b e and a t t a c h t h e backup s e c t i o n t o a p o r t a b l e pump. S e t t h e f l o w r a t e a t 30 t o 75 ml p e r m i n u t e . Sample volume s h o u l d n o t e x c e e d 15 l i t e r s . 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 , cap t h e ends o f t h e t u b e s and mark f o r l a t e r i d e n t i f i c a t i o n . R e t u r n t h e sample t u b e s t o t h e a p p r o p r i a t e l a b o r a t o r y and s t o r e i n a r e f r i g e r a t o r p r i o r t o a n a l y s i s .

ANALYTICAL PROCEDURE a) b) c) d)

e) f) g) h)

i) j) k) 1)

Uncap t h e sample t u b e and remove t h e g l a s s wool f r o m the p r i m a r y s e c t i o n . Make s u r e t h a t no p a r t i c l e s a d h e r e t o t h e g l a s s wool p l u g . T r a n s f e r t h e XAD-2 r e s i n f r o m t h e p r i m a r y s e c t i o n i n t o a screw-cap v i a l . Pipet 2 m i l l i l i t e r s of fluorescamine s o l u t i o n into the v i a l and c a p t h e c o n t a i n e r as t i g h t l y as p o s s i b l e . Shake t h e v i a l s v i g o r o u s l y by hand f o r 30 s e c o n d s and w i t h a " r o c k i n g " m o t i o n wash t h e XAD-2 r e s i n p a r t i c l e s t o t h e b o t t o m o f t h e v i a l i n o r d e r t o a c h i e v e good contact with the fluorescamine s o l u t i o n . P l a c e t h e sample i n t h e Brinkman-Chromato-Vue U l t r a v i o l e t box f o r 15 m i n u t e s a t t h e l o n g wave U.V. setting. Remove t h e v i a l f r o m t h e box. F l u s h t h e 10-jul l o o p w i t h 1 ml o f C O - f r e e m e t h a n o l . S w i r l t h e sample s o l u t i o n . D i p t h e n e e d l e i n t o t h e sample s o l u t i o n i n t h e d e s o r p t i o n v i a l and w i t h d r a w t h e p l u n g e r u n t i l t h e volume o f t h e sample i n t h e s y r i n g e r e a c h e s 40 u l . Make s u r e t h e r e a r e no a i r b u b b l e s i n t h e i n j e c t i o n fluid. I n j e c t the e n t i r e contents of the s y r i n g e into the sample i n j e c t i o n system. Measure t h e peak h e i g h t o r a r e a and d e t e r m i n e t h e MIC c o n c e n t r a t i o n from a p r e v i o u s l y prepared c a l i b r a t i o n curve. A n a l y z e t h e backup ( s m a l l ) s e c t i o n o f t h e a d s o r p t i o n t u b e i n t h e same manner as t h e p r i m a r y . I f t h e MIC c o n t e n t o f t h e backup s e c t i o n i s f o u n d t o e x c e e d 25 p e r c e n t o f t h e q u a n t i t y i n t h e p r i m a r y s e c t i o n , the p o s s i b i l i t y e x i s t s that p a r t of the vapors have p a s s e d t h r o u g h t h e t u b e w i t h o u t b e i n g a d s o r b e d . In t h e e v e n t t h i s o c c u r s , t h e a i r s a m p l i n g w i l l have t o be r e p e a t e d , t a k i n g a s m a l l e r t o t a l volume o f a i r through the tube.


7.

Determination

VINCENT AND K E T C H A M

of Methyl

Isocyanate

147

m)

A n a l y z e t h e b l a n k t u b e i n t h e same manner as t h e s a m p l e tube. n) A l l a i r samples must be d e s o r b e d a t t h e same t i m e a s t h e s t a n d a r d s i n o r d e r t o o b t a i n a c c u r a t e measurements o f t h e a c t u a l MIC c o n c e n t r a t i o n s c o l l e c t e d o n t h e adsorbent. 10* CALIBRATION CURVE a)


b) c) d) e) f)

g)

h) 11.

P i p e t 1 ml o f t e t r a h y d r o f u r a n i n t o e a c h o f 5 s c r e w - c a p vials. U s i n g a 1 0 - u l H a m i l t o n S y r i n g e , i n j e c t 0.5, 1, 2, 5, and 7.5 m i c r o l i t e r s o f MIC i n t o r e s p e c t i v e v i a l s . S w i r l e a c h v i a l . T h e s e s t a n d a r d s c o n t a i n 0.476, 0.952, 1.90, 4.76, and 7.14 m i c r o g r a m s o f MIC p e r m i c r o l i t e r . S t o r e standards i n a r e f r i g e r a t o r u n t i l needed. W i t h a 1 0 - u l H a m i l t o n S y r i n g e , i n j e c t one m i c r o l i t e r o f e a c h s t a n d a r d i n t o r e s p e c t i v e p r e v i o u s l y p r e p a r e d XAD-2 resin tubes. A l l s t a n d a r d t u b e s s h o u l d be d e s o r b e d a t t h e same t i m e as t h e a i r s a m p l e s t h a t w e r e c o l l e c t e d i n t h e f i e l d . T h i s i s t o i n s u r e t h a t t h e c o n c e n t r a t i o n measurements a r e a c c u r a t e and p r e c i s e . I n j e c t these standards i n t o the chromatograph u s i n g the i n j e c t i o n t e c h n i q u e d e s c r i b e d i n S e c t i o n 9, A n a l y t i c a l Procedure. S w i r l the v i a l each time p r i o r t o w i t h d r a w i n g a sample. P l o t peak a r e a o r h e i g h t v e r s u s m i c r o g r a m s o f MIC p e r milliliter.

CALCULATION (A-B) χ 24.45 χ 2 χ 760 χ (Τ + 273) ' V χ MW χ Ρ χ

1

. „ ' ° n

P

P

m

m

f M

M T r I C

A

= m i c r o g r a m s o f MIC p e r ml o b t a i n e d f r o m c a l i b r a t i o n curve Β = m i c r o g r a m s o f MIC i n b l a n k MW = m o l e c u l a r w e i g h t o f MIC ( 5 7 . 0 5 ) V = t o t a l volume o f a i r sampled i n l i t e r s Ρ = p r e s s u r e (mm Hg) o f a i r sampled Τ = t e m p e r a t u r e (°C) o f a i r sampled 760 = s t a n d a r d p r e s s u r e (mm Hg) 273 = s t a n d a r d t e m p e r a t u r e (°K)

12.

REFERENCE

7-RSC-69

RECEIVED October 22, 1979.

American Chemicef Society Library 1155 16th St. N. W.

In Analytical Techniques in Occupational Health Chemistry; Dollberg, D., et al.; Washington, D. C. Society: 20036Washington, DC, 1980. ACS Symposium Series; American Chemical

A New Fluorescence Procedure for the Determination of Methyl

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