Ion Chromatographic Analysis of Formic Acid in Diesel Exhaust and

38 Ion Chromatographic Analysis of Formic Acid in Diesel Exhaust and Mine Air I T A M A R B O D E K and

KENNETH

Downloaded by NORTH CAROLINA STATE UNIV on January 7, 2013 | http://pubs.acs.org Publication Date: April 2, 1981 | doi: 10.1021/bk-1981-0149.ch038

Arthur D . Little, Incorporated,

T.

MENZIES

Cambridge, M A 02140

Formaldehyde, a suspected carcinogen (1) and known i r r i t a n t ( 2 ) , i s found at low concentrations i n d i e s e l engine exhaust and i n environments subjected to d i e s e l emissions ( 3 ) . A typical concentration i n d i e s e l exhaust i s 5-25 ppm and about one hundred times lower i n a mine atmosphere subjected to such exhaust ( 3 ) . The f a t e of formaldehyde i n mines i s of i n t e r e s t to mine workers and operators due to i t s p o t e n t i a l h e a l t h hazard. I t has been suggested that o x i d a t i o n of formaldehyde to formic a c i d may occur i n the mine environment and thus reduce i t s concentration (4). Previous attempts to measure concentrations of formic a c i d at ppm l e v e l s have been thwarted by inadequate d e t e c t i o n l i m i t s . Genera l l y , a n a l y t i c a l methods f o r formic a c i d employ c o l l e c t i o n i n aqueous s o l u t i o n s and r e a c t i o n with o x i d i z i n g or reducing agents. Measurement of formic a c i d at high concentrations can be made by adding an excess of o x i d i z i n g agent and t i t r a t i n g the remaining excess of oxidant with reducing agents ( 5 ) . Another method (6) r e l i e s on the d i s t i l l a t i o n of a chloroform-formic a c i d azeotrope to separate formic a c i d from higher c a r b o x y l i c a c i d s and a n a l y s i s of the formic a c i d by potentiometric t i t r a t i o n with sodium hydroxide. Detection l i m i t s f o r t h i s method are g e n e r a l l y i n the 0.1% range (6). Gas chromatography has been used to measure formic a c i d both d i r e c t l y and a f t e r d e r i v i t i z a t i o n . D i r e c t a n a l y s i s poses problems of c o r r o s i o n of metal surfaces and of high detect i o n l i m i t s with a flame i o n i z a t i o n detector. D e r i v i t i z a t i o n (7) e l i m i n a t e s these problems and achieves a d e t e c t i o n l i m i t of about 25 yg/mL. Ion chromatography has r e c e n t l y been s u c c e s s f u l l y used f o r a n a l y s i s of formaldehyde a f t e r o x i d a t i o n to formic a c i d (8) and thus can be used f o r d i r e c t a n a l y s i s of formic a c i d . In order to prevent i n t e r f e r e n c e with such i n o r g a n i c anions as f l u o r i d e , c h l o r i d e , and n i t r a t e which occurs with Na2C03/NaHC0 eluents, a weak aqueous eluent, i . e . , Na2B 0y, was used to achieve adequate separation. The d e t e c t i o n l i m i t i n such an i o n chromatographic a n a l y s i s i s l i m i t e d by the conductance of the suppressed eluents, but the development of ion chromatography e x c l u s i o n (ICE), 3

i+

0097-6156/81/0149-0599$05.00/0 © 1981

American Chemical Society

In Chemical Hazards in the Workplace; Choudhary, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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which permits separation of weak a c i d s i n a lower conductance background, has circumvented t h i s problem. The determination of weak acids i n complex media (9) has been reported with t h i s technique. This paper describes the a n a l y s i s of formic a c i d i n d i e s e l engine exhaust and mine a i r using i o n chromatography (IC) and i o n chromatography e x c l u s i o n (ICE).


Experimental C o l l e c t i o n . Formic a c i d i n d i l u t e d (1:10) d i e s e l exhaust or mine a i r was c o l l e c t e d by drawing the sample atmosphere through two f r i t t e d bubblers (10) i n s e r i e s , each containing 15 mL of 10" M Na C03. A flow r a t e of 1.0 l i t e r per minute and c o l l e c t i o n time of 60 minutes f o r d i l u t e d d i e s e l exhaust or 240 minutes f o r mine a i r was used. A 37 mm g l a s s f i b e r f i l t e r (Gelman Type A/E) was placed before the bubblers to remove p a r t i c u l a t e s . 3

2

A n a l y s i s . The s o l u t i o n i n each bubbler was t r a n s f e r r e d to a 25 mL volumetric f l a s k and d i l u t e d to volume with the c o l l e c t i o n medium (10~ M Na2C0 ). In the case of samples c o l l e c t e d from d i l u t e d d i e s e l exhaust, an excess (3 mL) of t h i s s o l u t i o n was flushed through a 100 yL sample loop of Dionex Model 14 i o n chromatograph. The sample was analyzed on the anion system with i n strumental c o n d i t i o n s presented i n Table I. 3

3

Table I Ion Instrument: Eluent: Flow Rate: Detector: Sensitivity: Anion Columns:

Sample Volume: Recorder: Chart Speed:

Chromatographic Conditions Dionex Model 14 Ion Chromatograph 0.005 M N a B 0 2.3 mL/min. Conductivity 30 ymho f u l l s c a l e 3 x 125 mm Dionex Anion Pre-column 3 x 500 mm Dionex Separator (Borate Form) 6 x 250 mm Dionex Suppressor (H+ Form) 100 yL Sample Loop HP 7133A 0.5 cm/min. 2

4

7

In the case of samples c o l l e c t e d from mine a i r , the bubbler s o l u t i o n was concentrated by freeze d r y i n g . Samples were t r a n s f e r r e d to wide mouth j a r s , f r o z e n to -25°C and f r e e z e - d r i e d under 0.5 cm Hg vacuum i n a Vacudyne, Inc. P i l o t Freeze Dryer. Once reduced to dryness, 1 mL of d i s t i l l e d / d e i o n i z e d water was added to the samples. A f t e r shaking to ensure complete d i s s o l u t i o n , 300 yL a l i q u o t s were placed i n micro v i a l s a v a i l a b l e f o r use i n a Waters A s s o c i a t e s A u t o i n j e c t o r Model 710 A. One hundred yL sample


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volumes were a u t o m a t i c a l l y i n j e c t e d i n t o t h e i o n c h r o m a t o g r a p h and a n a l y z e d on t h e i o n c h r o m a t o g r a p h y e x c l u s i o n ( I C E ) s y s t e m w i t h instrumental conditions presented i n Table I I . TABLE I I


Ion

Chromatographic E x c l u s i o n

Instrument: Eluent: Flow Rate: Detector: Sensitivity: ICE Columns:

(ICE) C o n d i t i o n s

D i o n e x M o d e l 14 I o n C h r o m a t o g r a p h 0.0001 M HC1 0.7 mL/min. Conductivity 3 ymho f u l l s c a l e 9 x 250 mm D i o n e x E x c l u s i o n 3 x 500 mm D i o n e x H a l i d e S u p p r e s s o r (Ag Form) 100 y L , W a t e r s A s s o c i a t e s A u t o i n j e c t o r ( M o d e l 710 A) HP 7133A 0.5 cm/min. +

Sample Volume: Recorder: C h a r t Speed: R e s u l t s And

Discussion

A n a l y t i c a l M e t h o d . I n i t i a l e x p e r i m e n t s w e r e c o n d u c t e d on t h e D i o n e x M o d e l 14 i o n c h r o m a t o g r a p h t o d e t e r m i n e t h e f e a s i b i l i t y and s e n s i t i v i t y o f i o n c h r o m a t o g r a p h i c a n a l y s i s o f f o r m i c a c i d . The c o n d i t i o n s o f IC a n a l y s i s ( T a b l e I ) c h o s e n w e r e b a s e d on t h e need f o r s e p a r a t i o n o f f o r m a t e i o n f r o m common a t m o s p h e r i c c o n t a m i n a n t s , s u c h as c h l o r i d e i o n , and o t h e r o r g a n i c a n i o n s , s u c h as a c e t a t e . The c o n d i t i o n s were a l s o o p t i m i z e d t o o b t a i n a s u i t able detection l i m i t . T h u s , a weak b o r a t e e l u e n t (0.005 M Na Bi+C>7) combined w i t h a 500 mm a n i o n s e p a r a t o r column (and a 150 mm p r e c o l u m n ) was c h o s e n . C o n v e r s i o n o f t h e p r e - c o l u m n and s e p a r a t o r c o l u m n t o t h e i r b o r a t e forms ( f r o m t h e n o r m a l c a r b o n a t e f o r m ) was necessary. The p r o c e s s o f c o n t i n u a l l y p a s s i n g t h e b o r a t e e l u e n t t h r o u g h t h e columns u n t i l a s t a b l e b a s e l i n e was o b t a i n e d r e q u i r e d s e v e r a l hours. S t a n d a r d s t o c k s o l u t i o n s of f o r m a t e a n i o n were p r e p a r e d from r e a g e n t grade sodium f o r m a t e . S t a n d a r d s o l u t i o n s o f o t h e r o r g a n i c a n i o n s were p r e p a r e d f o r assessment of p o t e n t i a l i n t e r f e r e n c e s . I n j e c t i o n s o f 3 mL w e r e made t o f i l l a sample l o o p o f 100 yL v o l ume. A t y p i c a l i o n c h r o m a t o g r a m o f f o r m a t e and a c e t a t e i s shown i n F i g u r e 1. Peak i d e n t i f i c a t i o n s and c o n c e n t r a t i o n s a r e r e p o r t e d as the f r e e a c i d s t o f a c i l i t a t e sample a n a l y s i s . The r e t e n t i o n t i m e s f o r a c e t a t e and f o r m a t e u n d e r t h e s e c o n d i t i o n s a r e 6.6 and 8.8 minutes, r e s p e c t i v e l y . The p r e c e d i n g n e g a t i v e peak g r o u p i n g s e e n i n t h e 2-5 m i n u t e r e g i o n i s due t o w a t e r whose c o n d u c t i v i t y i s lower than b o r i c a c i d . The peak h e i g h t i s l i n e a r w i t h f o r m i c a c i d c o n c e n t r a t i o n o v e r t h e r a n g e f r o m 0.1 t o 35 yg/mL. The c o r r e 2


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Formic Acid

1.5/xg/ml Formic Acid and Acetic

Acetic Acid

Acid

Inject

A

IW Anion System

Figure 1.

Ion chromatogram of formic acid and acetic acid


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sponding l i n e a r range f o r a c e t i c a c i d i s about 0.2 to 70 yg/mL. The presence of f l u o r i d e or c h l o r i d e i n the sample does not i n t e r f e r e with the formic a c i d a n a l y s i s . Retention time f o r these ions under the s t a t e d c o n d i t i o n s are F~ (5.4 minutes) and CI" (29 minutes). S u l f a t e i o n i s r e t a i n e d f o r a longer time. U l t i m a t e l y , these anions are e l u t e d and may i n t e r f e r e with subsequent samples. Generally, these h i g h l y r e t a i n e d anions show very broad peaks, which are e a s i l y d i s t i n g u i s h e d from the organic a c i d peaks. Due to t h i s i n t e r f e r e n c e , the need f o r frequent regeneration of the suppressor column and the a b i l i t y of i o n chromatography e x c l u s i o n to e a s i l y separate organic a c i d s and C l ~ and S 0 i , an ICE system was t e s t e d f o r s i m i l a r analyses. T y p i c a l ICE c o n d i t i o n s (Table I I ) provide easy s e p a r a t i o n of s t r o n g l y i o n i z e d species (e.g., i^SO^, HC1, HNO3) from weakly i o n i z e d species (e.g., organic a c i d s ) due to the greater r e t e n t i o n of uncharged species i n the i n t e r s t i t i a l f l u i d of the packing m a t e r i a l (9). A c i d i c eluents reduce the i o n i z a t i o n of weak organic a c i d s and thus i n c r e a s e t h e i r r e t e n t i o n time. A 10 M hydrochloric acid eluent o f f e r s adequate s e p a r a t i o n of the strong a c i d s and the organic a c i d s of i n t e r e s t with a reasonable r e t e n t i o n p e r i o d . Standard stock s o l u t i o n s were prepared as before and i n j e c t e d onto the i o n chromatograph. In order to u t i l i z e very small sample volumes, the normal sample loop, which r e q u i r e s excess sample, was by-passed and a Waters A s s o c i a t e s A u t o i n j e c t o r (Model 710 A) installed. One hundred yL i n j e c t i o n s were made d i r e c t l y i n t o the flowing eluent by the a u t o i n j e c t o r and analyzed on the ICE system. A t y p i c a l i o n chromatogram of formic a c i d and s u l f u r i c a c i d i s shown i n Figure 2. The r e t e n t i o n time f o r the s u l f u r i c a c i d and formic a c i d are 9.8 and 15.4 minutes, r e s p e c t i v e l y . The peak height i s l i n e a r with formic a c i d c o n c e n t r a t i o n over the range of 0.3 to 10 yg/mL. The corresponding l i n e a r range f o r a c e t i c a c i d i s 3 to 100 yg/mL (Figure 3). As w e l l as p r o v i d i n g s e p a r a t i o n of these organic a c i d s and p r e c l u d i n g i n t e r f e r e n c e from strong acids, the ICE system permits continuous a n a l y s i s of samples f o r up to 30 hours without regeneration of the suppressor column. =


+

_I+

The p r e c i s i o n of the ICE method was determined by a n a l y z i n g s i x r e p l i c a t e s of two standard s o l u t i o n s c o n t a i n i n g strong a c i d s ( i . e . , K^SO^) and s e v e r a l weak a c i d s ( i . e . , formic a c i d , a c e t i c a c i d and carbonic a c i d ) . Carbonic a c i d i s present as a r e s u l t of the use of Na2C0 i n the standard s o l u t i o n matrix (as i n the c o l l e c t i o n medium) and d i s s o l u t i o n of atmospheric carbon d i o x i d e (Figure 4). At formic a c i d concentrations of 5.0 and 10 mg/L, the measured mean concentrations (Table I I I ) were 5.08 and 10.0 mg/L, r e s p e c t i v e l y . The r e l a t i v e standard d e v i a t i o n (CV) was 0.025 and 0.016, r e s p e c t i v e l y . 3

C o l l e c t i o n Method. The goal of the i n i t i a l phase of our work was to determine the c o n c e n t r a t i o n of formic a c i d i n engine exhaust subject to d i f f e r e n t forms of c o n t r o l , e.g., c a t a l y t i c o x i d a t i o n . I n i t i a l l y , samples were c o l l e c t e d from d i e s e l engine



Inject

10/ig/ml

/

Figure 2.

Formic Acid

Add

20

ICE

Minutes

System

ICE chromatogram of formic acid and other strong acids

Acids

Strong

Formic


r > o m

O

H W

O

>

> r

x

n

o

ON


Figure 3.

Standard curve for ICE system: (%) formic acid, (O) acetic acid

PEAK HEIGHT (mm)


as o

oo


Inject

,71fff

Mine Sample

Figure 4.

Strong Acids

I 20

30

ICE System

Carbonic Acid

Chromatogram of mine sample

Formic Acid

Minutes



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TABLE I I I Formic A c i d A n a l y t i c a l Data Calculated Concentration (yg/mL)

Observed Concentration (yg/mL)

5.00

5.23 5.18 5.18 4.95 4.95 5.01 Mean Std Dev CV

5.08 0.127 0.025 10.2 10.2 10.1 9.9 10.1 9.8

10.00

Mean Std Dev CV

10.0 0.163 0.016


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exhaust d i l u t e d by a f a c t o r o f 10 i n a s t a i n l e s s s t e e l d i l u t i o n tunnel. A c o l l e c t i o n medium of 15 mL of 10" M sodium carbonate s o l u t i o n was u t i l i z e d f o r two reasons. F i r s t , such an aqueous s o l u t i o n (7) i s reported to provide good c o l l e c t i o n e f f i c i e n c y of s o l u b l e organic a c i d s a t flow r a t e s of 0.5 to 5 L/min. Second, due to the v o l a t i l i t y of f r e e formic a c i d , i t was f e l t that a b a s i c s o l u t i o n would provide improved s t a b i l i t y of the samples over periods up to seven days. The c o l l e c t i o n e f f i c i e n c y o f t h i s medium was determined by measuring the amount of formic a c i d c o l l e c t e d a t 1.0 L/min i n two bubblers connected i n s e r i e s . The amount of formic a c i d found i n the f r o n t and back bubbler at three challenge concentrations produced i n the d i l u t i o n tunnel i s r e ported i n Table IV and shows that the c o l l e c t i o n e f f i c i e n c y i s greater than 92%.


3

TABLE IV Collection Efficiency Challenge Concentration (mg/m ) 3

12 6.7 2.5 0.06

y% Formic A c i d Found Front Back 153 90.0 32.5 10.3

% Collection i n Front

92.3 92.2

In order to provide a t l e a s t 99% c o l l e c t i o n of formic a c i d i n d i l u t e d exhaust, two bubblers were r o u t i n e l y used i n s e r i e s . In a l a t e r phase of work, the formic a c i d c o n c e n t r a t i o n i n mine a i r subject to d i e s e l emissions was measured. The expected conc e n t r a t i o n s were about one hundred times lower than those found i n engine exhaust. The e f f i c i e n c y of the c o l l e c t i o n scheme was again measured under these c o n d i t i o n s of challenge c o n c e n t r a t i o n (0.06 mg/m ). The c o l l e c t i o n e f f i c i e n c y was found to be 92.2% at t h i s l e v e l (Table IV). 3

Sample A n a l y s i s . F o r sample c o l l e c t i o n i n both d i l u t e d d i e s e l exhaust and a mine atmosphere, the c o l l e c t i o n technique described p r e v i o u s l y was used, and the sampling periods were 60 minutes and 240 minutes, r e s p e c t i v e l y . In the mine samples, the amount of formic a c i d c o l l e c t e d was too small to be analyzed r e l i a b l y a f t e r d i l u t i o n to 25 mL. Larger amounts could have been c o l l e c t e d by u t i l i z i n g a higher flow r a t e (e.g., 5 L/min) or longer sampling p e r i o d . However, i n order to u t i l i z e the samples as c o l l e c t e d , they were concentrated by f r e e z e - d r y i n g . The pH of samples was checked p r i o r to f r e e z e - d r y i n g to ensure that the s o l u t i o n s were s l i g h t l y b a s i c . Strongly a c i d i c s p e c i e s , e.g., H S 0 , formed i n the bubblers by o x i d a t i o n and h y d r a t i o n of S 0 during mine a i r sampling, slowly depleted the Na C03 i n the c o l 2

4

2

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l e c t i o n medium. Weakly i o n i z e d organic a c i d s may be l o s t i f a s u f f i c i e n t l y low pH i s achieved. Recovery of formic a c i d during the f r e e z e - d r y i n g process was checked by c a r r y i n g standard s o l u t i o n s through the e n t i r e a n a l y t i c a l procedure. As i s shown i n Table V, recovery of t r i p l i c a t e samples at two concentrations averaged about 0.88. TABLE V


Formic A c i d Recovery A f t e r Freeze-Drying I n i t i a l Sample Concentration (yg/mL)

Freeze-Dried Sample Concentration (yg/mL)

Recovery

4.3

3.9 3.7 3.9

0.91 0.86 0.91

9.7

9.0 8.3 7.8

0.93 0.86 0.80

Storage s t a b i l i t y of these samples was checked by r e p l i c a t e a n a l y s i s a f t e r a p e r i o d of seven days. Losses of l e s s than 2% were observed a f t e r storage f o r t h i s p e r i o d of time. The accuracy of the ICE method was assessed by using the standard a d d i t i o n technique. Four mine samples c o n t a i n i n g measured concentrations of formic a c i d of about 0.8 to 1.1 yg/mL were spiked with a known volume f o r formate standard s o l u t i o n s u f f i c i e n t to double the sample c o n c e n t r a t i o n . The observed concent r a t i o n i n d i c a t e d agreement of b e t t e r than ±12% with an average agreement w i t h i n ±5% (Table V I ) . TABLE VI Standard A d d i t i o n of Formic A c i d Initial Concentration (yg/mL) 0.8 1.0 1.1 1.1

With Spike C a l c u l a t e d Observed 1.6 2.0 2.2 2.2

1.8 2.1 2.3 2.2

Agreement 1.12 1.05 1.04 1.00

Standard a d d i t i o n was a l s o used to confirm the i d e n t i f i c a t i o n of the chromatographic peaks based on comparison of r e t e n t i o n time. No i n t e r f e r e n c e was observed due to c h l o r i d e , s u l f a t e or carbonate i o n . Both formate and acetate were adequately r e s o l v e d .


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A small u n i d e n t i f i e d peak d i d precede formic a c i d but did not s i g n i f i c a n t l y affect quantitation. Samples of d i l u t e d d i e s e l engine ( i . e . , Ford 2401 E, 50 horsepower) exhaust were c o l l e c t e d under s e v e r a l c o n d i t i o n s of engine speed and load and a p p l i c a b l e c o n t r o l technology to determine t h e i r impact on the emission of formic a c i d . Two to s i x r e p l i c a t e samples were c o l l e c t e d under each t e s t c o n d i t i o n , and the mean c o n c e n t r a t i o n i s reported i n Table VIII t i s g e n e r a l l y apparent that at a higher speed and load (higher engine temperature), the c o n c e n t r a t i o n of formic a c i d i s lower presumably due to more complete combustion. The c a t a l y s t has l i t t l e impact except at the higher speed and load c o n d i t i o n where the c a t a l y s t i s at an elevated temperature and thus where i t s o x i d a t i o n e f f i c i e n c y i s greater. The water c o n d i t i o n e r , which i s normally i n s t a l l e d on d i e s e l engines i n underground c o a l mines, shows a s i g n i f i c a n t r e d u c t i o n of formic a c i d c o n c e n t r a t i o n which i s probably due to i t s s o l u b i l i t y i n water. To determine the f a t e of formaldehyde and formic a c i d i n a c o a l mine, an unused s h a f t about 120 m long and 6 m i n cross s e c t i o n a l area was s e l e c t e d f o r study. With a v e n t i l a t i o n a i r flow of 190 m /min and an engine exhaust flow of 1.5 m /min, complete exhaust d i s p e r s i o n and d i l u t i o n was observed i n about 10 m. Samples c o l l e c t e d i n the mine a i r downstream of the d i e s e l engine i n d i c a t e no s i g n i f i c a n t change i n formic a c i d concentrat i o n at i n c r e a s i n g distances from the engine (Table V I I I ) . This i s c e r t a i n l y not c o n s i s t e n t with the l o s s of formaldehyde i n the same i n t e r v a l . The mechanism f o r l o s s of formaldehyde i s appare n t l y not a gas phase o x i d a t i o n to formic a c i d . I n t e r a c t i o n with surfaces may be a more s u i t a b l e explanation of the observed reduct i o n i n formaldehyde concentrations. 2

3

3

Conclusions Two i o n chromatographic techniques were u t i l i z e d to q u a n t i f y formic a c i d i n both d i e s e l engine exhaust and mine a i r subjected to d i e s e l emissions. A commonly used anion s e p a r a t i o n system u t i l i z i n g a weak borate eluent adequately separated the a c i d s of i n t e r e s t i n d i e s e l exhaust. I t was, however, a f f e c t e d by the presence of strong a c i d s during subsequent consecutive analyses. In order to preclude t h i s problem and the necessary frequent regeneration of the anion system's suppressor column, an i o n chromatography e x c l u s i o n scheme was u t i l i z e d . Samples c o l l e c t e d i n a mine environment were r e l i a b l y concentrated by f r e e z e - d r y i n g and then analyzed on an ICE system with d i l u t e h y d r o c h l o r i c a c i d eluent. The p r e c i s i o n of the ICE method was experimentally determined to be ±2.5% i n a c o n c e n t r a t i o n range of 1 to 10 yg/mL. The accuracy was not independently determined but good p r e c i s i o n and recovery y i e l d confidence that measured values are w i t h i n ±5% of the true value. No i n t e r f e r e n c e s were observed i n the ICE system due to strong a c i d s , carbonic a c i d or other water s o l u b l e species present i n mine a i r subject to d i e s e l emissions.


38.

BODEK

A N D MENZIES

Formic

Acid

in Diesel

611

Exhaust

TABLE VII Formic A c i d i n Engine Exhaust Formic Acid Relative Engine Percent Concentration Standard Condition (RPM) Load (%) (mg/m ) Deviation

Control Device

3


None

Monolithic Catalyst (Exhaust Cont r o l s , Inc. )

C a t a l y s t and Water Conditioner (MSA, Inc.)

1,000 1,800 2,650

0 16 34

13.0 9.8 5.6

0.09 0.05 0.10

1,000 1,800 2,650

0 16 34

12.0 9.4 1.7

0.15 0.01 0.14

1,000 1,800 2,650

0 16 34

3.0 2.1 0.5

0.14 0.10 0.10

TABLE V I I I Fate of Formaldehyde and Formic A c i d i n Mine Formaldehyde Formic A c i d Distance from Concentration^ Concentration Engine (m) ( 1 0 ~ mg/m ) ( I P " mg/m ) 3

0 15 46 77 108 a Background ^Measured

a

3

4.6 62 31 18 20

3

8.5 62 62 61 66

concentration upstream of engine exhaust.

by chromotropic a c i d method (11).


3

612

CHEMICAL

H A Z A R D S IN T H E W O R K P L A C E


Results o f a n a l y s i s o f formic a c i d i n d i e s e l engine exhaust s u b j e c t e d t o v a r i o u s forms o f p o s t - c o m b u s t i o n c o n t r o l , i . e . , c a t a l y t i c o x i d a t i o n and w a t e r c o n d i t i o n i n g , i n d i c a t e b o t h a reduct i o n o f f o r m i c a c i d due t o o x i d a t i o n i n t h e c a t a l y s t a n d d i s s o l u t i o n i n the water scrubber. In-mine a n a l y s i s o f f o r m i c a c i d a t i n c r e a s i n g d i s t a n c e s from a source o f d i e s e l exhaust i n d i c a t e s t h a t no s i g n i f i c a n t change i n c o n c e n t r a t i o n o c c u r s . This f i n d i n g c o n t r a d i c t s a hypothesis that formaldehyde c o n c e n t r a t i o n decreases w i t h i n c r e a s i n g d i s t a n c e due t o g a s p h a s e o x i d a t i o n t o f o r m i c acid. S u r f a c e r e a c t i o n s may, however, be i m p o r t a n t s i n k s f o r formaldehyde.

Abstract Low molecular weight carboxylic acids are among the highly water soluble compounds that are difficult to quantify by conventional organic analytical procedures. The relatively new technique of ion chromatography has the potential for analyzing these acids in complex matrices. Concentrations of formic acid found in samples of diluted diesel exhaust and coal mine air were determined using two ion chromatographic procedures. Samples were collected in midget bubblers containing dilute sodium carbonate solutions. Analysis of formate ion in these solutions was performed using a 500 mm anion separator column and sodium borate eluent. Analysis of formate in these solutions was also performed using the ion chromatography exclusion mode (ICE) using the Dionex IE-C-1 column with dilute hydrochloric acid eluent. Retention time for formate ion using the borate system is 11 minutes at a flow rate of 2.3 mL/min. Fluoride, chloride, sulfate and acetate do not interfere in the analysis. Linear response is obtained over the concentration range of 0.1-4 µg/mL. The detection limit is estimated at 0.05 µg/mL for an injection volume of 100 µL at 3 µmhos full scale sensitivity. The ICE system was used to confirm the identity of the formate detected in the samples and determine its concentration. The retention time for formate using the ICE system at an eluent flow rate of 0.7 mL/min is 16 minutes. No interference is observed from chloride, sulfate and acetate. Linear response is obtained for formate in the concentration range of 1-20 µg/mL. The detection limit for a 100 µL sample injection volume at 30 µmhos full scale sensitivity is estimated at 0.5 µg/mL. Concentration of samples by freeze-drying affords better detection limits with minimal loss of formic acid. Acetic and carbonic acids are also analyzable under these conditions.


38. BODEK AND MENZIES

Formic Acid in Diesel Exhaust

613


Literature Cited 1.

Billings, C. E. "Industrial Pollution"; Sax, N. I., Ed.: Van Nostrand Rheinhold Co.: New York, NY, 1974; p. 120.

2.

Patty, F. A., Ed. "Industrial Hygiene and Toxicology", Second Revised Edition, Volume II, Toxicology; Interscience Publishers: New York, NY, 1963; p. 1959.

3.

Lawter, J. R.; Kendall, D. A. "Effects of Diesel Emissions on Coal Mine Air Quality"; Final Report, U.S. Bureau of Mines Contract JO166009, 1977.

4.

Menzies, K. T. "Fate of Reactive Diesel Exhaust Contaminants"; Draft Final Report, U.S. Bureau of Mines Contract JO188061, 1980.

5.

Peters, D. G.; Hayes, J. M.; Hieftze, G. M. "Chemical Separations and Measurements"; Saunders Co.: New York, NY; 1974; p. 180.

6.

Warner, B. R.; Raptis, L. Z. Anal. Chem., 1955, 27, 1978.

7.

Smallwood, A. W. Amer. Ind. Hyg. Assoc. J., 1978, 39, 151.

8.

Kim, W. S.; Geraci, C. L.; Kupel, R. E. Amer. Ind. Hyg. Assoc. J., 1980, 41, 334.

9.

Rich, W.; Smith, F. C.; McNeil, L.; Sidebottom, T. "Determination of Strong and Weak Acids and Their Salts by Ion Chromatography Coupled with Ion Exclusion"; unpublished, available from Dionex, Inc.

10.

U.S. Public Health Service "Selection Methods for the Measurement of Air Pollutants"; Publication No. 999-AP-ll, May 1965.

11.

Katz, M., Ed. "Methods of Air Sampling and Analysis", Second Edition; American Public Health Association: Washington, D.C., 1977; p. 303.

RECEIVED

October 27, 1980.


Ion Chromatographic Analysis of Formic Acid in Diesel Exhaust and

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