Determination of Ozone in Air by Neutral and Alkaline Iodide Procedures

Determination of Ozone in Air by Neutral and Alkaline Iodide Procedures D. H. BYERS and Β. E. SALTZMAN

Downloaded by CORNELL UNIV on June 1, 2012 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0021.ch013

Occupational Health Program, Public Health Service, U. S. Department of Health, Education, and Welfare, 1014 Broadway, Cincinnati 2, Ohio

O n e per cent potassium iodide in neutral buffered or alkali solutions is more stable a n d useful than 20% potassium iodide in bubblers for collection and de termination of ozone in air. Either 1 % solution may be used to determine low concentrations of ozone; however, there is a difference in their stoichiometry. O v e r the range of 0.01 to 30 p.p.m. (v./v.) results by the alkaline procedure should be multiplied by 1.54 to correct for stoichiometry. The neutral reagent does not require acidification a n d has more nearly uniform stoichiometry. The alkaline procedure is preferable when final analysis may be delayed. Ex periments with boric acid for acidification of samples in the alkaline reagent show that some mechanism other than oxidation of iodide to iodate or periodate is involved, possibly formation of hypoiodite. Prelim inary experiments with gas phase titrations of nitrogen dioxide a n d nitric oxide against ozone confirm the stoichiometry of the neutral reagent as 1 mole of iodine released for each mole of ozone.

T h e d e t e r m i n a t i o n of c o n c e n t r a t i o n s of ozone i n a i r i n t h e range of a f e w p a r t s p e r m i l l i o n h a s b e c o m e i n c r e a s i n g l y i m p o r t a n t as a result of c u r r e n t t o x i c o l o g i c a l a n d a i r p o l l u t i o n s t u d i e s . T o x i c c o n c e n t r a t i o n s of ozone m a y be e n c o u n t e r e d i n h i g h a l t i t u d e flights, as w e l l as i n r o c k e t w o r k a n d i n i n e r t g a s - s h i e l d e d a r c w e l d i n g . O z o n e also a p p e a r s t o p l a y a k e y role i n c e r t a i n s m o g - f o r m i n g processes, as w e l l as i n t h e g e n e r a t i o n of eye i r r i t a n t s a n d p l a n t - d a m a g i n g substances. A l t h o u g h a g r e a t m a n y m e t h o d s f o r ozone d e t e r m i n a t i o n s h a v e b e e n e m p l o y e d (6, 10), t h e u n c e r t a i n s t o i c h i o m e t r y a n d t h e l a c k of s p e c i f i c i t y c o n t i n u e t o be serious p r o b l e m s . T h e i o d i d e c h e m i c a l m e t h o d s a p p e a r e d t o be a m o n g t h e m o s t p r o m i s i n g , a n d were selected f o r i n v e s t i g a t i o n . M a n y w o r k e r s h a v e u s e d i o d o m e t r i c m e t h o d s f o r t h e d e t e r m i n a t i o n of c o n c e n t r a t i o n s of ozone i n t h e r a n g e of s e v e r a l p e r c e n t b y v o l u m e a n d h i g h e r . T h e y h a v e i n v e s t i g a t e d t h e s t o i c h i o m e t r y b y c o m p a r i s o n of t h e a m o u n t s of i o d i n e l i b e r a t e d w i t h t h e a m o u n t s of ozone d e t e r m i n e d b y p h y s i c a l m e a s u r e m e n t s of gas d e n s i t y o r p r e s s u r e c h a n g e . T h u s L e c h n e r (5) f o u n d t h a t b o t h n e u t r a l a n d a l k a l i n e (02N p o t a s s i u m h y d r o x i d e ) p o t a s s i u m i o d i d e (0.2M) a b s o r b e d ozone efficiently a n d y i e l d e d t h e same a m o u n t of i o d i n e , e q u i v a l e n t t o one o x y g e n a t o m i n t h e ozone m o l e c u l e . This 93

In OZONE CHEMISTRY AND TECHNOLOGY; Advances in Chemistry; American Chemical Society: Washington, DC, 1959.

A D V A N C E S IN CHEMISTRY SERIES

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s t o i c h i o m e t r y w a s c o n f i r m e d b y B o e l t e r , P u t n a m , a n d L a s h {2) f o r 4 t o 2 0 % ozone b y w e i g h t a b s o r b e d i n 0 . 2 M p o t a s s i u m i o d i d e b u f f e r e d t o v a r i o u s p H v a l u e s f r o m 2.3 t o 12.3. I n a n o t h e r r e c e n t s t u d y b y B i r d s a l l , J e n k i n s , a n d S p a d i n g e r ( 1 ) , s i m i l a r r e s u l t s w e r e o b t a i n e d f o r 1 t o 2 5 m o l e % ozone (1.7 t o 4 1 w e i g h t % ) a b s o r b e d i n 2 % unbuffered potassium iodide, b u t results w i t h boric acid-buffered solutions were high. T h e d i s c r e p a n c y b e t w e e n B i r d s a l l ' s findings a n d those of B o e l t e r w a s e x p l a i n e d b y t h e difference i n s a m p l i n g e q u i p m e n t : B o e l t e r o b t a i n e d g o o d r e s u l t s w i t h a c i d s o l u t i o n s b e cause h e u s e d a n a b s o r p t i o n b u l b i n w h i c h t h e s u r f a c e r e a c t i o n s c o u l d cause l o c a l a l k a l i n i t y a t t h e p o i n t a t w h i c h ozone w a s a b s o r b e d . B i r d s a l l used a bubbler i n w h i c h a b s o r p t i o n p r o c e e d e d a t t h e a c i d p H o f t h e b u l k of t h e s o l u t i o n . A l t h o u g h t h e r e a r e also c o n t r a r y r e p o r t s i n t h e l i t e r a t u r e , t h e use of b o t h n e u t r a l a n d a l k a l i n e i o d i d e s o l u t i o n s f o r d e t e r m i n a t i o n of h i g h c o n c e n t r a t i o n s o f ozone seems t o b e e s t a b l i s h e d . S i m i l a r p r o c e d u r e s h a v e b e e n a p p l i e d t o t h e d e t e r m i n a t i o n of l o w c o n c e n t r a t i o n s of ozone i n t h e p a r t s p e r m i l l i o n r a n g e . R e n z e t t i a n d R o m a n o v s k y (6) r e p o r t e d t h a t i n L o s A n g e l e s a i r t h e n e u t r a l m e t h o d gives a p p a r e n t l y l o w r e s u l t s ( p e r h a p s d u e t o r e d u c i n g pollutants) i n t h e early a n d late hours of t h e d a y , a n d h i g h results (perhaps due t o o t h e r o x i d i z i n g p o l l u t a n t s ) d u r i n g t h e p e a k s m o g t i m e o f d a y , b o t h as c o m p a r e d t o u l t r a v i o l e t s p e c t r o p h o t o m e t r i c d e t e r m i n a t i o n s o f ozone. S m i t h a n d D i a m o n d (9) r e c o m m e n d e d a reagent c o n s i s t i n g o f 1 % p o t a s s i u m i o d i d e i n IN s o d i u m h y d r o x i d e , a c i d i f i e d a f t e r s a m p l i n g w i t h % v o l u m e of 3 6 % p h o s p h o r i c a c i d t o release t h e i o d i n e for spectrophotometric estimation. T h i s was modified b y B y e r s , S a l t z m a n , a n d H y s l o p (3), w h o f o u n d t h a t t h e i n t e r f e r e n c e f r o m n i t r o g e n d i o x i d e c o u l d b e g r e a t l y reduced, a n d t h e colors stabilized, i f t h e acid were saturated w i t h sulfamic a c i d , w h i c h d e s t r o y s n i t r i t e . T h e s p e c i f i c i t y w a s i n v e s t i g a t e d b y E f f e n b e r g e r (4), w h o u s e d O.OliV p o t a s s i u m i o d i d e b u f f e r e d t o v a r i o u s p H v a l u e s . T h e a m o u n t s of i o d i n e l i b e r a t e d b y ozone v a r i e d f r o m 9 0 % a t p H 9 t o 1 1 3 % a t p H 1, as c o m p a r e d t o t h a t a t p H 7. F o r n i t r o g e n d i o x i d e t h e v a r i a t i o n w a s m u c h g r e a t e r , t h e c o r r e s p o n d i n g figures b e i n g 7 0 a n d 3 4 0 % . T h u s t h e t w o c o u l d be d i s t i n g u i s h e d b y s i m u l t a n e o u s a n a l y s e s a t t w o different p H v a l u e s . S a l t z m a n (8) b e l i e v e d t h e 1 % p o t a s s i u m i o d i d e i n IN s o d i u m h y d r o x i d e reagent m o r e specific t h a n t h e n e u t r a l reagents i n t h e presence of o x i d i z e d hexene, a n d he also r e p o r t e d 6 2 t o 7 0 % s t o i c h i o m e t r y f o r 3 t o 2 7 p . p . m . ( v . / v . ) ozone (as c o m p a r e d t o t h e i o d i n e released i n a n e u t r a l r e a g e n t ) . T h e v a l i d i t y o f t h e a p p l i c a t i o n of n e u t r a l a n d a l k a l i n e i o d i d e reagents t o t h e d e t e r m i n a t i o n of l o w c o n c e n t r a t i o n s o f ozone w a s therefore investigated. T h e p r e p a r a t i o n of k n o w n l o w c o n c e n t r a t i o n s o f ozone h a s a l w a y s b e e n a m a j o r d i f f i c u l t y i n t h i s t y p e o f i n v e s t i g a t i o n . A flow s y s t e m w a s set u p i n w h i c h a s t r e a m of ozone f r o m a d i e l e c t r i c - t y p e o z o n i z e r c o u l d b e d i l u t e d w i t h a i r p u r i f i e d b y s c r u b b i n g w i t h dichromate i n concentrated sulfuric acid, followed b y c a l c i u m chloride a n d silica gel. F l o w s w e r e m e a s u r e d w i t h r o t a m e t e r s a n d c o u l d b e a d j u s t e d t o g i v e k n o w n d i l u t i o n r a t i o s . T h e reagents were u s e d f o r w i d e ranges of u n d i l u t e d a n d d i l u t e d ozone c o n c e n t r a t i o n s , a n d s a m p l e s of w i d e l y v a r y i n g sizes were c o l l e c t e d . T h e a s s u m p t i o n w a s m a d e t h a t t h e h i g h concentration analyses were l i k e l y to be correct, a n d t h e deviations r e s u l t i n g f r o m v a r y i n g t h e s a m p l e sizes a n d f r o m t h e d i l u t i o n w e r e s t u d i e d . Ozone

Procedures

Reagents. T h r e e reagents w e r e t e s t e d e x t e n s i v e l y : r e a g e n t I , 2 0 % p o t a s s i u m iodide i n 0 . 1 M potassium dihydrogen p h o s p h a t e - 0 . 1 M disodium hydrogen phosphate; r e a g e n t I I , 1 % p o t a s s i u m i o d i d e i n t h e s a m e n e u t r a l p h o s p h a t e buffer m e d i u m ; a n d reagent I I I , 1 % p o t a s s i u m i o d i d e i n IN s o d i u m h y d r o x i d e , a c i d i f i e d a f t e r s a m p l i n g w i t h 1 / 5 v o l u m e of 3 6 % p h o s p h o r i c a c i d s a t u r a t e d w i t h s u l f a m i c a c i d . R e a g e n t I w a s p r e pared fresh a n d used w i t h i n several hours. R e a g e n t s I I a n d I I I were a l l o w e d t o s t a n d f o r s e v e r a l d a y s b e f o r e b e i n g u s e d . T h i s s t a b i l i z e d t h e b l a n k . W i t h e a c h reagent i t was necessary t o determine t h e reagent b l a n k a n d to deduct i t f r o m a l l standardizations a n d d e t e r m i n a t i o n s . O n l y t h e h i g h e s t g r a d e a n a l y t i c a l reagents w e r e u s e d . R e a g e n t I is c o m m o n l y u s e d i n o x i d a n t r e c o r d e r s

(6), b u t w a s t o o u n s t a b l e a n d


BYERS A N D SALTZMAN—DETERMINATION

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AIR

photosensitive for the usual m a n u a l procedures. R e a g e n t I I y i e l d e d a l m o s t as m u c h i o d i n e as reagent I w i t h m u c h s u p e r i o r s t a b i l i t y . R e a g e n t I I I p r o v e d t h e m o s t s u i t a b l e f o r field studies w h e r e h o u r s o r d a y s m i g h t elapse b e t w e e n c o l l e c t i n g a n d a n a l y z i n g t h e samples.


S a m p l i n g . S a m p l e s were c o l l e c t e d i n 10 m l . of reagent i n m i d g e t i m p i n g e r s u s i n g a i r - f l o w rates of 1 t o 3 l i t e r s p e r m i n u t e . O t h e r s i m p l e b u b b l e r s m a y b e u s e d ; how ever, t h e m i d g e t i m p i n g e r is m o s t c o n v e n i e n t a n d effective. S a m p l i n g of h i g h c o n c e n t r a t i o n s b y e v a c u a t e d flasks w a s t r i e d a n d f o u n d u n s u i t a b l e . Measurements. I o d i n e l i b e r a t e d b y t h e ozone w a s m e a s u r e d p h o t o m e t r i c a l l y or t i t r i m e t r i c a l l y . T h e i o d i n e a b s o r b a n c e a t 352-ηΐμ, w a v e l e n g t h w a s m e a s u r e d b y a B e c k m a n D U spectrophotometer. T e s t t u b e s of 2 - c m . l i g h t p a t h a n d m a t c h e d t o 0 . 5 % t r a n s m i t t a n c e were u s e d i n a s p e c i a l h o l d e r . D i s t i l l e d w a t e r w a s u s e d i n t h e reference tube. T i t r a t i o n s were m a d e w i t h O.OOôAf s o d i u m t h i o s u l f a t e i n a s e m i m i c r o b u r e t a n d using a visual end point w i t h starch indicator. Procedures a n d standardization. Reagents I a n d I I . A f t e r collection, the s a m ples w e r e t r a n s f e r r e d i m m e d i a t e l y t o p h o t o m e t e r t u b e s a n d t h e a b s o r b a n c e s d e t e r m i n e d . S t a n d a r d g r a p h s of a b s o r b a n c e vs. i o d i n e ( o r ozone) were p l o t t e d f r o m r e a d i n g s f r o m a series of p r e p a r e d s t a n d a r d s . S t a n d a r d 0 . 0 1 0 0 N i o d i n e s o l u t i o n w a s f r e s h l y d i l u t e d w i t h reagent s o l u t i o n t o v a r i o u s s t r e n g t h s f r o m zero t o 0.00004Af (5.08 γ of i o d i n e p e r m l . ) a n d t h e a b s o r b a n c e s were d e t e r m i n e d . T h e ozone e q u i v a l e n t w a s c a l c u l a t e d o n t h e basis of 0 Ο I (1 m l . of 0.0 L/V I Ο 240 γ of 0 ) . 3

2

2

3

R e a g e n t I I I . T h e p h o s p h o r i c a c i d reagent f o r use w i t h t h e a l k a l i n e r e a g e n t w a s p r e p a r e d as f o l l o w s : S e v e r a l g r a m s of reagent q u a l i t y s u l f a m i c a c i d w e r e d i s s o l v e d i n 150 m l . of w a r m d i s t i l l e d w a t e r , t h e n 126 m l . of 9 0 % p h o s p h o r i c a c i d w e r e a d d e d a n d t h e m i x t u r e was made to 300-ml. volume w i t h distilled water. A f t e r cooling, the precipitated sulfamic a c i d w a s r e m o v e d b y décantation ( o r c e n t r i f u g a t i o n ) a n d s a v e d f o r p r e p a r a t i o n of f u t u r e b a t c h e s of reagent. S a m p l e s i n 10 m l . of t h e a l k a l i n e i o d i d e reagent were r a p i d l y a c i d i f i e d a n d m i x e d w i t h 2.0 m l . of p h o s p h o r i c a c i d r e a g e n t . T h e m i x t u r e ( i n a s t o p p e r e d c o n t a i n e r ) w a s c o o l e d t o r o o m t e m p e r a t u r e i n a w a t e r b a t h , a n d t h e a b s o r b a n c e d e t e r m i n e d 5 t o 10 minutes after acidification. A s t r o n g s t o c k s o l u t i o n of p o t a s s i u m i o d a t e (0.2973 g r a m p e r l i t e r ) w a s d i l u t e d 1 t o 10 w i t h d i s t i l l e d w a t e r t o g i v e a d i l u t e s t a n d a r d , 1 m l . of w h i c h w a s e q u i v a l e n t t o 105.8 γ o f i o d i n e . A l i q u o t s of 0.1 t o 0.5 m l . of t h i s d i l u t e s t a n d a r d were d i l u t e d t o 10 m l . w i t h reagent I I I a n d a c i d i f i e d a n d t h e a b s o r b a n c e s r e a d . C a l c u l a t i o n s w e r e o r i g i n a l l y m a d e o n t h e basis of 3 0 Ο K I 0 (1 m l . of d i l u t e s t o c k Κ Ι 0 Ο 20 γ of 0 ) . T h e w o r k s h o w e d t h e n e e d f o r a c o r r e c t i o n f a c t o r of 1.54 w h i c h w o u l d m a k e 1 m l . of d i l u t e s t o c k Κ Ι 0 Ο 30.8 y of 0 . 3

3

Calculation. c u l a t i o n o f ozone

3

3

3

3

T h e following relationship m a y be used rather t h a n graphs for c a l concentrations: P.p.m. 0

3

= Κ A/V

w h e r e A is t h e a b s o r b a n c e c o r r e c t e d f o r t h e b l a n k , V i s t h e v o l u m e i n l i t e r s of a i r s a m p l e d ( c o r r e c t e d t o 2 5 ° C . a n d 7 6 0 m m . of m e r c u r y ) , a n d Κ i s t h e s t a n d a r d i z a t i o n factor. F o r 2 - c m . t u b e s Κ w a s 4.61 f o r reagent I , 4.88 f o r r e a g e n t I I , a n d 9.13 f o r reagent I I I . T h e l a s t figure i s h i g h e r because i t i n c o r p o r a t e s t h e c o r r e c t i o n f a c t o r a n d because t h e c o r r e s p o n d i n g a b s o r b a n c e s a r e l o w e r e d b y t h e d i l u t i o n of t h e s a m p l e t o 12 m l . b y the acidification. Effects o f S a m p l e S i z e T h e u n d i l u t e d ozone c o n c e n t r a t i o n s r a n g e d f r o m 3 0 0 t o 5000 p . p . m . , d e p e n d i n g u p o n t h e flow r a t e a n d o x y g e n c o n t e n t of t h e gas p a s s i n g t h r o u g h t h e o z o n a t o r , a n d




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SAMPLE VOLUME, ML. Figure 1.

SAMPLE VOLUME, ML.

Effect of sample size on photometric determinations of high concentrations of ozone Left. Neutral 2 0 % Kl reagent Right. Alkaline Kl reagent

t h e v o l t a g e a p p l i e d . T h e p h o t o m e t r i c d e t e r m i n a t i o n of these levels u s i n g reagents I a n d I I I h a d (8) b e e n f o u n d u n s a t i s f a c t o r y because of t h e e x t r e m e d i l u t i o n s r e q u i r e d t o p e r m i t r e a d i n g s i n t h e p h o t o m e t e r a n d of a n o n l i n e a r r e l a t i o n s h i p b e t w e e n t h e a m o u n t s of i o d i n e a n d s a m p l e sizes as s h o w n i n F i g u r e 1. T h i s figure gives t h e d a t a o b t a i n e d b y s i m u l t a n e o u s l y s a m p l i n g w i t h c a l i b r a t e d e v a c u a t e d b o t t l e s of v a r i o u s sizes, c o n t a i n i n g these reagents. T h e a m o u n t s of i o d i n e w e r e e s t i m a t e d p h o t o m e t r i c a l l y , a n d some of t h e h i g h e r a m o u n t s were c h e c k e d b y t i t r a t i o n . T h e p l o t s s h o w t h e total absorbance (the measured absorbance, corrected for the b l a n k , m u l t i p l i e d b y the d i l u t i o n f a c t o r ) f o r 2 - c m . cells vs. s a m p l e size. T h e n e u t r a l m e t h o d w i t h 2 0 % p o t a s s i u m i o d i d e (reagent I ) g a v e c u r v e d lines i n the useful p h o t o m e t r i c region, w h i c h a p p r o a c h e d straight lines only a t absorbances r e q u i r i n g e x t r e m e d i l u t i o n s . T h e v a l u e s i n d i c a t e d f o r ozone w e r e a s s i g n e d o n t h e basis of t h e l i m i t i n g slopes of t h e c u r v e s a t h i g h v a l u e s . T h e a l k a l i n e m e t h o d (reagent I I I ) gave a l m o s t s t r a i g h t l i n e s , w h i c h seemed t o c o n v e r g e t o a n e g a t i v e a b s o r b a n c e a t zero s a m p l e v o l u m e . T h i s n e g a t i v e a b s o r b a n c e i n t e r c e p t m a y b e r e g a r d e d as t h e " o z o n e d e m a n d " of t h e reagent, a n d w a s f o u n d f o r b o t h e v a c u a t e d b o t t l e a n d i m p i n g e r s a m p l e s a t h i g h c o n c e n t r a t i o n s . T h e ozone d e m a n d a p p e a r e d t o increase w i t h t h e age of t h e reagent, a n d w a s r e d u c e d s o m e w h a t b y t h e a d d i t i o n of i o d a t e t o t h e s a m p l i n g reagent t o p r o d u c e a r t i f i c i a l l y a n a p p r e c i a b l e p o s i t i v e i o d i n e b l a n k . T h i s ozone d e m a n d w a s f a i r l y c o n s t a n t t h r o u g h a s m a l l r a n g e of ozone c o n c e n t r a t i o n s , b u t i n c r e a s e d s o m e w h a t a t m u c h h i g h e r a b s o r b a n c e s a n d ozone c o n c e n t r a t i o n s . T h e reasons f o r these discrepancies are n o t k n o w n . S u b s e q u e n t l y h i g h c o n c e n t r a t i o n s of ozone were d e t e r m i n e d b y t i t r i m e t r i c p r o -


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cedures. E f f e c t s of e r r o r s d u e t o s a m p l e size were t h u s m i n i m i z e d b y l i b e r a t i o n of l a r g e r a m o u n t s of i o d i n e . R e a g e n t s I I a n d I I I were u s e d s u c c e s s f u l l y f o r p h o t o m e t r i c d e t e r m i n a t i o n of l o w c o n c e n t r a t i o n s of ozone, as o n l y s l i g h t d i s c r e p a n c i e s r e s u l t e d f r o m v a r i a t i o n s of s a m p l e size. T h i s is s h o w n i n F i g u r e 2, w h i c h also shows a difference i n s t o i c h i o m e t r y . T h e m i d g e t i m p i n g e r w i t h 10 m l . of reagent w a s u s e d a t s a m p l i n g flow rates of 1, 2 , a n d 3 l i t e r s of a i r p e r m i n u t e . T h e differences i n flow rates h a d l i t t l e o r n o effect e x c e p t as t h e y d e t e r m i n e d t h e v o l u m e s a m p l e d . B o t h reagents s h o w g o o d l i n e a r r e l a t i o n s h i p s of a b s o r b a n c e a n d s a m p l e size f o r ozone c o n c e n t r a t i o n s i n t h e 0.1 t o 20 p . p . m . ( v . / v . )

SAMPLE

VOLUME

(LITERS)

Figure 2. Effect of sample size on photometric determinations of low concentration (4.25 p.p.m.) of ozone with neutral and alkaline 1 % potassium iodide reagents range. T h e results b y the alkaline procedure are consistently lower, w i t h a tendency t o a n i n c r e a s i n g p r o p o r t i o n of i o d i n e f o r v e r y l a r g e s a m p l e s . Effects of O z o n e

Concentration

A n a l y s e s w i t h reagents I I a n d I I I were c o m p a r e d a t b o t h h i g h a n d l o w c o n c e n t r a t i o n s . L o w c o n c e n t r a t i o n s were o b t a i n e d b y a c c u r a t e l y d i l u t i n g h i g h c o n c e n t r a t i o n ozone 1 t o 99 w i t h p u r i f i e d a i r . S i m u l t a n e o u s s a m p l e s were c o l l e c t e d a n d a n a l y z e d , w i t h the results given i n T a b l e I . T h e t w o methods give fair agreement at concen t r a t i o n s of s e v e r a l t h o u s a n d p a r t s p e r m i l l i o n , b u t d i v e r g e a t l o w e r c o n c e n t r a t i o n s , t h e results b y t h e a l k a l i n e p r o c e d u r e b e i n g c o n s i s t e n t l y l o w e r . M e a s u r e m e n t s of t h e d i l u t e d ozone b y t h e n e u t r a l reagent g a v e a b o u t 8 5 % of t h e c a l c u l a t e d v a l u e w i t h l i t t l e v a r i a t i o n , w h i l e t h e a l k a l i n e reagent gave m u c h l o w e r a n d m o r e e r r a t i c r e s u l t s . I n a s m u c h as p a i r e d s a m p l e s were c o l l e c t e d s i m u l t a n e o u s l y , t h e differences c o u l d n o t b e due t o fluctuations i n ozone c o n c e n t r a t i o n s . S u b s e q u e n t tests r e v e a l e d a 6 % loss of ozone i n t h e s y s t e m b e t w e e n t h e p o i n t of s a m p l i n g t h e h i g h c o n c e n t r a t i o n a n d t h e p o i n t of d i l u t i o n . I t a p p e a r s t h a t t h e s t o i c h i o m e t r y of reagent I I is m o r e n e a r l y c o n s t a n t w i t h s u c h changes of c o n c e n t r a t i o n .


98


T a b l e I. Simultaneous Determinations of Undiluted and Diluted O z o n e Concentrations b y Reagents II and III (Neutral and Alkaline) Reagent II, P . P . M .


Undiluted 5350 5050 4310 3510 3030 1895 1413 1280 980 791 547 473 453 439 437 433 425

Relative V a l u e s

by

Reagent III, P . P . M . Undiluted 4760 5400 4250 4360 3045 1650 1262 1125 808 636 600 379 394 374 375 384 353

Diluted 1/100

25.1 15.9 14.4 11.5 8.13 6.70 4.92 3.56 3.78

3.81

Neutral

and

Alkaline

Diluted 1/100

14.4 11.4 9.72 8.19 4.06 3.67 3.69 2.73 2.56

2.53

Reagents

I n F i g u r e 3 t h e r e l a t i o n s h i p b e t w e e n a n a l y s e s b y t h e n e u t r a l a n d a l k a l i n e reagents I , I I , a n d I I I is shown for corresponding samples collected simultaneously or at v e r y close i n t e r v a l s o v e r a w i d e r a n g e of ozone c o n c e n t r a t i o n s . B e c a u s e of t h e e x t r e m e r a n g e of c o n c e n t r a t i o n s a l o g - l o g p l o t i s u s e d . C o n c e n t r a t i o n s a b o v e 100 p . p . m . ( v . / v . ) were determined t i t r i m e t r i c a l l y ; below this, photometrically. T h e differences b e t w e e n a l k a l i n e a n d n e u t r a l analyses c a n n o t b e e x p l a i n e d b y differences i n a b s o r p t i o n efficiencies, as t h e y were h i g h w i t h a l l t h r e e r e a g e n t s . When t w o i m p i n g e r s w e r e u s e d i n series, t h e s e c o n d n e v e r s h o w e d m o r e t h a n a f e w p e r cent of t h e a m o u n t of i o d i n e released i n t h e first i m p i n g e r . V e r y l i t t l e ozone w a s d e s t r o y e d b y t h e w a t e r , a l k a l i , o r s a m p l i n g a p p a r a t u s . W h e n IN s o d i u m h y d r o x i d e (reagent I I I w i t h o u t p o t a s s i u m i o d i d e ) w a s u s e d i n t h e first of t w o i m p i n g e r s i n series, 8 5 t o 9 0 % of t h e ozone p a s s e d i n t o t h e s e c o n d i m p i n g e r . T h e a p p a r e n t l y l o s t ozone w a s d i s s o l v e d i n t h e a l k a l i , a n d b y t h e a d d i t i o n of p o t a s s i u m i o d i d e a n d a c i d i t released i o d i n e

Figure 3. Determination of ozone in duplicate samples with neutral a n d alkaline reagents


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f o r i t s d e t e r m i n a t i o n . T h u s i t seemed l i k e l y t h a t t h e absence of i o d i n e i n a s e c o n d s a m p l e r w a s s i g n i f i c a n t , a n d t h a t t h e a b s o r p t i o n efficiencies w e r e h i g h . D i f f e r e n c e s l i k e w i s e c a n n o t b e e x p l a i n e d o n t h e basis of s t a n d a r d i z a t i o n . T h e n e u t r a l reagents were s t a n d a r d i z e d b y a d d i n g d i l u t e i o d i n e s o l u t i o n s , a n d t h e a l k a l i n e reagent b y a d d i n g s t a n d a r d p o t a s s i u m i o d a t e . T h e i o d i n e e x t i n c t i o n coefficients i n u n i t s of a b s o r p t i o n ( t o l o g a r i t h m i c base 10) p e r c e n t i m e t e r p e r g r a m p e r l i t e r w e r e : ( I ) 104, ( I I ) 9 9 , ( I I I ) 9 7 . T h e s l i g h t l y h i g h e r coefficient f o r reagent I m a y b e e x p l a i n e d b y t h e h i g h e r i o d i d e c o n c e n t r a t i o n , w h i c h intensifies t h e i o d i n e c o l o r . T h e s l i g h t l y l o w coefficient f o r reagent I I I m a y b e d u e t o losses of i o d i n e i n t h e a c i d i f i c a t i o n procedure. A s s u m i n g t h a t t h e r e l a t i o n s h i p i n F i g u r e 3 w o u l d b e a s t r a i g h t l i n e , o r n e a r l y so, t h e best fit w a s d e t e r m i n e d b y t h e m e t h o d of least s q u a r e s . T h e p h o t o m e t r i c a l l y d e t e r m i n e d p o i n t s g a v e a l i n e w i t h a slope of 1.016, a n d a l l p o i n t s s h o w n g a v e a l i n e w i t h a slope of 1.045. C a l c u l a t e d r e l a t i o n s h i p s o f r e s u l t s a t s e v e r a l c o n c e n t r a t i o n s a c c o r d i n g t o t h e best fit of p h o t o m e t r i c d e t e r m i n a t i o n s are : 0 concentration, p.p.m. Alkaline/neutral, %

0.01 60

3

0.1 62

1.0 64

10 66

100 69

W h e n t h e d a t a f o r b o t h p h o t o m e t r i c a n d t i t r i m e t r i c r e s u l t s a r e fitted, t h e c o r r e s p o n d i n g v a l u e s b y a l k a l i n e d e t e r m i n a t i o n s r a n g e f r o m 50 t o 8 0 % of t h e n e u t r a l reagent r e s u l t . T h e s c a t t e r of r e s u l t s s h o w n b y F i g u r e 3 is s u c h t h a t t h e r e l a t i o n s h i p of a l k a l i n e to n e u t r a l analyses of 6 5 % , as i n d i c a t e d b y t h e l i n e A/N = 0.65 c a n be a p p l i e d o v e r the range of 0.01 t o 3 0 p . p . m . a n d p e r h a p s b e y o n d a t e i t h e r e n d w h i l e s t a y i n g w i t h i n the probable experimental error. Because the n e u t r a l analyses are presumed to be m o r e n e a r l y c o r r e c t , r e s u l t s of a l k a l i n e a n a l y s e s s h o u l d b e m u l t i p l i e d b y a c o r r e c t i o n f a c t o r of 1.54. Stoichiometry I t t h u s seems t h a t t h e a c t u a l r e a c t i o n b e t w e e n t h e ozone a n d t h e i o d i d e m u s t h a v e a different s t o i c h i o m e t r y i n a l k a l i n e s o l u t i o n . T h e r e a c t i o n b e t w e e n ozone a n d i o d i d e is c o m m o n l y g i v e n a s : 0

3

+ 2 H + 21- - » 0 + +

H2O

2

+ L

(1)

I n w e a k a l k a l i , t h e e q u i v a l e n t r e a c t i o n s f o r t h e same s t o i c h i o m e t r y a r e c o m m o n l y g i v e n as: (2)

30 + Ι--> 30 + Ι 0 3

2

3

followed upon acidification b y : lus" + 6 H + 51" -> 3I + 3 H 0 +

2

2

(3)

E x p e r i m e n t a l evidence indicates t h a t i n strong a l k a l i this p a t t e r n is n o t followed. W h e n p o r t i o n s of s a m p l e s i n reagent I I I were a c i d i f i e d t o p H 6.2 w i t h s o l i d b o r i c a c i d , t h e i o d i n e released w a s a p p r o x i m a t e l y 5 0 % o f t h a t r e s u l t i n g f r o m t h e u s u a l a c i d i f i c a t i o n t o p H 2. N o i o d i n e w a s o b t a i n e d f r o m reagent I I I w i t h a d d e d i o d a t e , u p o n a c i d i f i c a t i o n w i t h b o r i c a c i d . W i t h a d d e d p e r i o d a t e , s u c h a c i d i f i c a t i o n y i e l d e d 14 t o 2 0 % of t h e i o d i n e o b t a i n e d a t p H 2. T h i s c o m p a r e s w i t h 2 5 % r e p o r t e d f o r p e r i o d a t e b y W i l l a r d a n d M e r r i t t (11). A r e a s o n a b l e e x p l a n a t i o n of these d a t a w o u l d a p p e a r t o be t h e f o r m a t i o n of h y p o i o d i t e b y t h e f o l l o w i n g r e a c t i o n : I- + Os->IO- + 0

2

(4)

T h e d i s m u t a t i o n of h y p o i o d i t e t o g i v e i o d a t e a p p e a r s t o o c c u r o v e r a p e r i o d of m a n y h o u r s . A n o t h e r possible e x p l a n a t i o n c o u l d b e t h e f o r m a t i o n of i o d i t e . T h e s t o i c h i o m e t r y is b e i n g c o n f i r m e d i n a n i n d e p e n d e n t w a y b y gas t i t r a t i o n s . A s t r e a m of ozone i s m i x e d w i t h e i t h e r n i t r i c o x i d e o r n i t r o g e n d i o x i d e , a n d e n o u g h


A D V A N C E S IN

100

CHEMISTRY SERIES

flow t i m e is a l l o w e d f o r c o m p l e t e r e a c t i o n , a f t e r w h i c h ozone a n d n i t r o g e n d i o x i d e are d e t e r m i n e d . I n t h e f o r m e r case, t h e ozone is c o n v e r t e d t o a n e q u i v a l e n t a m o u n t of n i t r o g e n d i o x i d e : a

+

NO->O

+

A

NO

(5)

A

I n t h e l a t t e r case, t h e f o l l o w i n g r e a c t i o n occurs : 0

3

+

2N0 -> 0 2

2

+

N 0 2

5

(6)


A s R e a c t i o n 5 is 260 t i m e s as fast as 6, i n t h e presence of excess n i t r i c o x i d e , n o a p p r e c i a b l e q u a n t i t i e s of n i t r o g e n p e n t oxide n e e d be e x p e c t e d . Linear relationships are f o u n d b e t w e e n t h e a m o u n t s of ozone a n d t h e a m o u n t s of n i t r o g e n d i o x i d e g e n e r a t e d o r c o n s u m e d , t h e l a t t e r d e t e r m i n e d w i t h S a l t z m a n reagent (7). T h e s e s y s t e m s a p p e a r t o change v e r y s l u g g i s h l y w h e n t h e r e a c t a n t c o n c e n t r a t i o n s a r e c h a n g e d , p e r h a p s because of s u r f a c e effects, a n d t h e s y s t e m s a r e n o t y e t c o m p l e t e l y s a t i s f a c t o r y . T h e d a t a f o r one r u n i n w h i c h n i t r o g e n d i o x i d e w a s t i t r a t e d w i t h ozone a r e g i v e n

OZONE

Figure 4.

INPUT

(RP.MJ

Dynamic gas phase titration of N O 2 with O z o n e

N O 2 input held constant at 36 p.p.m. as O3 input was increased

i n F i g u r e 4. A d y n a m i c s y s t e m w a s used i n w h i c h t h e gases were m i x e d a t h i g h concentrations, allowed to react, t h e n diluted into a large chamber w i t h purified a i r . T h e n i t r o g e n d i o x i d e i n p u t w a s h e l d c o n s t a n t a n d t h e ozone i n p u t w a s v a r i e d . T h e ozone i n p u t t o t h e c h a m b e r w a s c a l c u l a t e d f r o m c a l i b r a t i n g r u n s w i t h o u t n i t r o g e n d i o x i d e . O z o n e w a s d e t e r m i n e d w i t h reagent I I I , c o r r e c t e d f o r s t o i c h i o m e t r y b y t h e f a c t o r 1.54. O z o n e analyses t o t h e l e f t of t h e e n d p o i n t ( l i n e D) represent t h e i n t e r ference of excess n i t r o g e n d i o x i d e , o r n i t r o g e n p e n t o x i d e , w i t h t h e a n a l y t i c a l m e t h o d . L i n e C shows t h e m u c h h i g h e r i n t e r f e r e n c e of N 0 w h e n s u l f a m i c a c i d is n o t a d d e d t o t h e p h o s p h o r i c a c i d reagent. A s h a r p e n d p o i n t is n o t o b t a i n e d , b u t c a n be e x t r a p o l a t e d w i t h a p p r o x i m a t e l y t h e c o r r e c t s t o i c h i o m e t r y . L i n e Β shows t h e c o n s u m p t i o n of n i t r o g e n d i o x i d e , a n d l i n e A shows t h e a c c u m u l a t i o n of excess ozone. 2

Comparison

of

Procedures

E i t h e r n e u t r a l o r a l k a l i n e i o d i d e p r o c e d u r e s m a y be a p p l i e d f o r d e t e r m i n a t i o n of ozone i n a i r ; t h e l a t t e r p r o c e d u r e r e q u i r e s use of a c o r r e c t i o n f a c t o r f o r s t o i c h i ometry.


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AIR

101


O n e of t h e a d v a n t a g e s of t h e a l k a l i n e p r o c e d u r e i s t h e r e l a t i v e s t a b i l i t y of t h e exposed reagent p r i o r t o a c i d i f i c a t i o n . T h i s p e r m i t s c o l l e c t i o n of s a m p l e s i n t h e field, a n d c o m p l e t i o n of t h e analyses i n t h e l a b o r a t o r y . I n one t e s t , a l i q u o t s of a p o o l e d a l k a l i n e s a m p l e were a c i d i f i e d a n d r e a d a t i n t e r v a l s f o r 3 d a y s a f t e r s a m p l i n g . M o s t of t h e loss of 10 t o 2 0 % w h i c h w a s o b s e r v e d o c c u r r e d i n t h e first d a y , so t h a t e v e n o l d e r s a m p l e s were p r a c t i c a b l e . S o m e l o t s of s a m p l i n g r e a g e n t b e h a v e d b e t t e r t h a n others i n t h i s respect. A s p e c i a l reagent i n w h i c h t h e s o d i u m h y d r o x i d e w a s o z o n i z e d , t h e n b o i l e d before a d d i t i o n of p o t a s s i u m i o d i d e , d i d n o t g i v e s i g n i f i c a n t l y higher results. T h e r e p r o d u c i b i l i t y of b o t h m e t h o d s f o r r e p l i c a t e s a m p l e s of ozone w a s n o t as precise as c o u l d b e e x p e c t e d f r o m t h e e x p e r i m e n t a l c o n d i t i o n s . R e a g e n t I I seemed t o be t h e best. I t s h o w e d m a x i m u m differences u p t o 5 % , w h i l e reagent I I I s h o w e d m a x i m u m differences u p t o 1 0 % , a n d a v e r a g e differences of a b o u t 5 % . A p p a r e n t l y t h e l a t t e r v a r i a t i o n s o c c u r r e d d u r i n g t h e ozone s a m p l i n g s t e p , as m u c h closer a g r e e m e n t w i t h reagent I I I w a s o b t a i n e d b y a c i d i f y i n g a l i q u o t s of a l a r g e p o o l e d s a m p l e . Reagent I I I required r a p i d acidification; u p o n v e r y slow acidification w i t h either ozone o r i o d a t e a d d e d , i o d i n e losses h a v e been o b s e r v e d . S i m i l a r losses o c c u r u p o n a d d i t i o n of s t a n d a r d i o d i n e t o t h e a l k a l i n e reagent before a c i d i f i c a t i o n , regardless of t h e r a t e of a c i d i f i c a t i o n , b u t n o t w h e n i o d i n e is a d d e d a f t e r a c i d i f i c a t i o n . A p p a r e n t l y i n t h e f o r m e r cases i o d i n e i s released a t t h e surface of a c i d d r o p s a n d a b s o r b e d i n t o t h e s u r r o u n d i n g a l k a l i , w h e r e t h e loss o c c u r s . W i t h r a p i d a c i d i f i c a t i o n of s a m p l e s t h e i o d i n e e x t i n c t i o n coefficient f o r reagent I I I agrees w e l l w i t h e x p e c t e d v a l u e s . A l i m i t e d a m o u n t of w o r k h a s b e e n c a r r i e d o u t o n t h e effect of p o l l u t a n t s . S u l f u r d i o x i d e decreased t h e a m o u n t o f i o d i n e l i b e r a t e d f r o m a l l r e a g e n t s ; t h e difference b e t w e e n reagents I I a n d I I I w a s s m a l l . N i t r o g e n d i o x i d e y i e l d e d 8 t o 1 1 % i n t e r ference w i t h reagent I I I , a n d a b o u t t h e same w i t h I I . F i v e tests w i t h 5 0 0 p . p . m . o f n i t r i c a c i d v a p o r s h o w e d a n a v e r a g e i n t e r f e r e n c e of 0.5 p . p . m . of ozone w i t h reagent I I I . Interferences f r o m other smog constituents have n o t been completely evaluated. C o m p a r a t i v e a n a l y s e s b y t h e t w o m e t h o d s of n a t u r a l a n d s y n t h e t i c (ozone-hexene) smogs g a v e a different p a t t e r n of r e s u l t s t h a n f o r o z o n e - a i r m i x t u r e s . I n some cases, a n a l y s e s b y t h e a l k a l i n e p r o c e d u r e g a v e r e s u l t s h i g h e r t h a n those b y t h e n e u t r a l p r o cedure. Acknowledgment T h e a u t h o r s a r e i n d e b t e d t o F . L . H y s l o p f o r e x t e n s i v e assistance w i t h a n a l y s e s . Literature

Cited

(1) B i r d s a l l , C. M., Jenkins, A. C., Spadinger, E., Anal. Chem. 24, 662-4 (1952). (2) B o e l t e r , E. D., Putnam, G. L., Lash, Ε. I., Ibid., 22, 1533-5 (1950). (3) B y e r s , D. H., Saltzman, Β. E., Hyslop, F. L., m i m e o g r a p h e d procedure, U. S. P u b l i c Health Service, 1955. (4) Effenberger, Ε., Z. anal. Chem. 134, 106-9 (1951-2). (5) Lechner, G., Z. Elektrochem. 17, 412-14 (1911). (6) R e n z e t t i , Ν. Α., R o m a n o v s k y , M. S., Arch. Ind. Health 14, 458-67 (1956). (7) Saltzman, Β. E., Anal. Chem. 26, 1949-55 (1954). (8) Saltzman, Β. E., Ind. Eng. Chem. 5 0 , 677-82 (1958). (9) Smith, R. G., Diamond, P. O., Am. Ind. Hyg. Assoc. Quart. 13, 235-8 (1952). (10) T h o r p , C. E., " B i b l i o g r a p h y of Ozone T e c h n o l o g y , " Vol. I, A r m o u r R e s e a r c h F o u n d a t i o n , Chicago, 1954. (11) Willard, H. H., Merritt, L. M., Jr., Ind. Eng. Chem., Anal. Ed. 14, 489-90 (1942). RECEIVED for review April 18, 1957.

Accepted June 19, 1957.


Determination of Ozone in Air by Neutral and Alkaline Iodide Procedures

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