Anal. Chem. 1985, 57, 1330-1335
1330
(19) Later, D. W.; Lee, M. 1.;Bartle, K. D.;Kong. R. C.; Vassillaros, D. L. Anal. Chern. 1981, 53, 1612-1620. (20) Wright, 6.W.; Peaden, P. A.; Lee, M. L.; Stark, T. J . Chromatogr. 1982,2 4 8 , 17-34. (21) Nishioka, M.; Bradshaw, J. S.;Lee, M. L.; Tominaga, Y.; Tedjamulla, M.; Castle, R. N. Anal. Chem. 1985, 57,309-312. 422) Nishioka, M.; Campbell, R. M.; West, w. R.; Smith, p. A,; Booth, G.M.; Lee, M. L.: Kudo, H . ; Castle, R. N., submitted for publication in Anal.
Chem .
RECEIVED for review November 30,1984. Accepted February 19, 1985. This work was supported by the Department of Energy, Office of Health and Environmental Research, Contract No. DE-AC02-79EV10237.
Solid Sorbent for Sampling of Sulfur Dioxide in Occupational Hygiene Knut Irgum* and Mats Lindgren Department of Analytical Chemistry, University of Umeb, S-901 87 Umeb, Sweden
Sulfur dioxide Is stabillred as an addltion compound with ethanedial after Initial hydrolysls. Reaction takes place on a partly regenerated poly(acrylic acld) weak cation exchange gel that Is used as buffering carrler for the stabillrer soiutlon. This results in high acidlbase buffer capacity without release of anions to the sample solution, whlch permits use of both colorimetric and Ion chromatographic determination. Breakthrough curves at dlfferent sampling temperatures and relative humldltles are presented. An 80-95 % S( I V ) recovery was obtained after storlng the sample on the tube for 2 weeks. I f the sample was stored desorbed In a refrigerator, recovery was 100%. Stabillring power of the sorbent was not affected by 4 months of storage prior to use. Equal concentrations were found with the sorbent and a buffered formaldehyde absorber when used in parallel In a fleld study. Precision of the sorbent method was, however, hlgher.
With widespread industrial use, documented acute ( 1 ) and suspected chronic ( 2 , 3 )toxicity of sulfur dioxide calls for a continuous development of the tools for monitoring the gas in the workplace. At the same time personal sampling devices are gaining increased popularity among occupational hygienists due to their convenience in use compared to impinger methods ( 4 ) . A number of solid sorbents for sulfur dioxide are already described in the literature (5-12). As several countries have separate TLV’s for sulfur species of different oxidation states, most of these (5-11) are, however, formally invalid, as they are unable to prevent sulfur dioxide from being oxidized after sampling. Some of them even involve an oxidation step prior to the determination of S02(g) as sulfate ion (10, 11). Passive diffusion badges (13)and untreated molecular sieves (12) have this speciation capability. The sensitivity of the diffusion badge is, however, insufficient for short-time sampling and molecular sieves demand specialized equipment for the determination of sulfur dioxide, which makes them unattractive to many users. The reaction of carbonyl compounds with hydrogen sulfite ions has recently been used for stabilization of sulfur dioxide after sampling (14, 15) and for preparation of standards for ion chromatography (16). The sampling method was originally developed for ambient monitoring, but the buffered formaldehyde absorber should also be of use in industrial hygiene,
in both impingers and diffusion badges. Stabilization of S(1V) by formaldehyde is superior to the classical West and Gaeke method (17), if the absorber is buffered to a p H between 4 and 5. Reactive aldehydes are therefore the reagents of choice in this application. A formaldehyde-based solid sorbent would permit sensitive and selective short-time sampling and make use of the same colorimetric determination as the diffusion badge, whose excellent long-time sampling characteristics it would complement. The volatility and instability of formaldehyde forced us, however, to search for another aldehyde in this application. A high buffer capacity was needed on the solid sorbent to compensate for the uneven distribution of sampled species on a sorbent tube, as compared to a solution. The water-retaining capacity of the sorbent had, furthermore, to be maximized t o ensure that the initial hydrolysis of sulfur dioxide takes place. The efforts made to accomplish this are the subject of this paper.
EXPERIMENTAL SECTION Reagents and Solutions. All chemicals were reagent grade, except 30% (w/v) aqueous ethanedial, benzaldehyde, and 3phenylpropenal (synth.; Merck-Schuchardt, Munich, FRG), acetaldehyde (f. biochem.; Merck, Darmstadt, FRG), DL-glyCeraldehyde (mp 135-138 “C; Aldrich, Beerse, Belgium), and dihydroxyacetone (“researchgrade”;Serva, Heidelberg, FRG). The pararosaniline (“standard grade”;Fluka, Buchs, Switzerland)was purified according to Scaringelli et al. (18). The following carriers were used: Amberlite XAD-2, XAD-7, and IRC-84 (H+ form) (pract.; Serva),active charcoal (2@-35 mesh for GC; Merck), 5-A molecular sieves (Kebo,Stockholm),and silica gel (Grace Type 58, 0.2-0.4 mm; Darex, Bad Homburg, FRG). All carriers were crushed (if necessary), washed carefully several times with methanol and water, dried, and sieved to 20-40 mesh before use. The mixed base for sample hydrolysis contained 20 mM formaldehyde and 0.5 M NaOH and was prepared fresh every third day. The color reagent was composed of 0.8 mM pararosaniline hydrochloride in 1 M HCl. Milli-Q (Millipore,Bedford, MA) deionized water was used throughout. WARNING: Pararosaniline and formaldehyde are suspected carcinogens and should be handled with due care. The Sorbent. One hundred grams moist Amberlite IRC-84 was converted to the Na+ form by stirring with 500 mL of 1 M NaOH for 30 min. It was then rinsed twice with water and reconverted to the H+ form with 1M HC1 by the same procedure. The acidic resin was carefully washed with water to remove excess hydrochloric acid and slurried in a volume of water just sufficient to cover the resin. The wet bed volume of the resin was estimated, and a volume of 0.5 M NaOH 3 times the wet bed volume was
0003-2700/85/0357-1330$01.50/00 1985 American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 57, NO. 7, JUNE 1985
added. The slurry was stirred continuously after the addition of NaOH to ensure even conversion of Hf into Na+. Completion of the reaction was monitored by measuring the pH of the solution, which dropped to less than 6 when the conversion was complete. The resin was filtered from this solution and carefully washed with water to remove sodium chloride produced during the conversion. The partly regenerated resin was dried at 70 'C until fairly dry and later a t 105 "C to constant weight. Ten milliliters of 2 M aqueous ethanedial was then added to 10 g of dry, partly regenerated resin, whereafter the sorbent was shaken until the liquid was soaked up by the resin. The sorbent was stored for at least 24 h before 200 A 10 mg aliquots were packed into 60 mm X 4 mm i.d. glass tubes where it was kept in position with wads of poly(tetrafluoroethy1ene)(PTFE) wool. The tubes were sealed with plastic caps and stored at room temperature until tested. The different carrier/stabilizer combinations examined before we settled for the one described above are compiled in Table I in the results and discussion section. One-milliliter portions of 2 M aqueous solutions (or saturated if limited by the solubility) of the stabilizer aldehydes were added per gram of dry resin. Aromatic aldehydes were applied to Amberlite XAD-2 by adding the appropriate aldehyde (5% of the polymer weight) as a 2% solution in methanol. Water was then added under stirring until the methanol concentration in the solution containing the polymer was less than 5%. Uptake was more than 98%. The coated polymer was filtered from the solution and tested without further drying. All sorbents were packed in glass tubes (see above) and tested at 20 OC by sampling from a test atmosphere containing 5 mg SOz(g)/m3a t 10% relative humidity (% RH) using a pumping rate of 200 mL/min. After being stored at room temperature for 24 h, the sorbents were desorbed and the solution was analyzed by ion chromatography. S(1V) and S(V1) signals were used to evaluate tetravalent and total sulfur recovery. Test Atmosphere Generation. Permeation tubes (19) made from 4 mm i.d. X 6 mm 0.d. fluorinated ethylene polymer (FEP) tubing of various lengths (mostly around 60 mm) were used as a source of S02(g). The ends were sealed with 8 mm pieces of 4.3 mm PTFE rod that were pressed into the tube and secured with 0.7 mm stainless steel wire that was coiled twice around the tube and twisted to crimp the tube around the plug. The tubes were purged with dried, purified air, having a temperature between 30 and 45 'C controlled to within f0.02 "C. This gas merged with another stream of purified air, with varied humidity. The mixture was homogenized by impinging on the wall of a 1-L glass container, where the sampling ports were situated. The system was washed with dilute phosphoric acid and dried without rinsing to avoid SOz(g)adsorption. To monitor the amount of SO,(@;)generated, a coulometric method (20) was used, as it permitted fast measurements of the SOz(g)concentration in the gas mixture without having to measure the flows of the gases mixed. A special instrument was built (21) to measure the % RH of the mixture. General ConditionsUsed in the Laboratory Tests. A 3-dm3 portion of the test atmosphere was pumped through the tube at a flow of 200 ml/min. An SKC AirChek Model 222-3 (SKC Corp., Eighty-Four, PA) personal sampler pump was used. The test atmosphere contained 5 mg of SOz(g)/m3at 20 "C and 50% RH. Deviations from these conditions are noted in each case. Ambient and test atmosphere temperatures were equal in the tests where temperature was varied. Breakthrough Curves. Breakthrough curves were recorded at 4,20, and 38 "C and at 10 and 50% RH at each temperature. The pressure side of the sampling pump was connected via Tygon tubing to a glass capillary purging the coulometric cell. The cell current, and thereby the amount of S02(g) passing the tube without being adsorbed, could thus be continuously recorded. Coulometric titrator settings were optimized so that the response time constant for a step change in gas concentration was less than 30 s. All of these tests were carried out on sorbent that had been stored for 2 months. Aqueous (2, 4, and 6 M) solutions of ethanedial were tested to find a suitable concentration of ethanedial in the stabilizer solution used for swelling the resin. A stabilizer solution/dry resin ratio of 1:l (v/w) was used. Breakthrough curves were then
1331
recorded at 10% RH, following the above procedure. A comparative test using pure water for swelling the resin was also included. Distribution of Sampled SOz(g)on the Tube. Test atmosphere and sampling parameters were identical with those in the storage tests below. After sampling, the sorbent was extracted from the tube in sections, each of 5 mm length (approximately 40 mg). Desorption and colorimetric determination (22) of the quantity of S02(g) trapped in each section followed. Storage Tests. Samples with 10,50, or 90% RH were used in the test atmosphere. SOz(g)concentration ranged from 1 to 25 mg/m3. After sampling, the tubes were stored for up to 2 weeks in a refrigerator at +4 "C or under normal fluorescent light at 20 "C. The sorbent had been prepared 4 months prior to testing, except for some tubes for controlling the presampling storability, where the sorbent was prepared the day before the test. Desorption was carried out according to the procedure below and was followed by colorimetric determination. Desorption of S02(g) from the Sorbent Tubes. The tubes were stored in a refrigerator for 24 h after sampling, whereafter the sorbent and the PTFE wad were transferred to a 5-mL desorption solution, which was water when colorimetry was used in the determination and 3.5 mM NaHC03 when ion chromatography was used. The desorption vessels were inverted immediately and at two additional times during the desorption. Some vials were treated in a Bransonic Model 221 ultrasonic bath for 5 min. The temperature of the desorption solution was 20 f 1 "C in all cases. A desorption time of 1 h with inversion every 15 min was used in all other experiments. Stability of Desorbed S(1V). Desorption was started immediately after sampling, and the vials were stored as in the storage tests. Determinations of the amount of stabilized SOz(g) in the solutions were done after recommended desorption for 1 h and after 7 and 25 days of storage, using the colorimetric procedure. Ion Chromatographic Determination. An ion chromatographic system with a Dionex 4 X 250 mm anion separator column (no. 030827), a 5.7 X 300 mm suppressor column packed with Bio-Rad AG 5OW-X16 (200-400 mesh), and a 100-rL sample loop was used for these analyses. An LDC Conductor Monitor with Model 7011 cell was used to monitor the conductivity. The eluent was 3.5 mM NazC03/2.6mM NaOH (16). Standards prepared according to ref 23 were used. Field Study. The tubes were field tested in a sulfite paper pulping plant at approximately 25 "C and 20% RH. Four parallel 15-min samples were taken from a common sampling port, using an SKC HFS 113 sampling pump with four 200 mL/min (nominally) flow restrictors. Two channels were connected to sorbent tubes and two to midget fritted glass impinger flasks containing 10 mL of buffered formaldehyde absorber (14).Sampling sites were chosen so as to maximize the variation in SOz(g) concentration. Some tubes were desorbed directly and stored in a refrigerator, while the remaining tubes were divided, half of them stored at room temperature under fluorescent light and the rest in a refrigerator. The samples from the impinger flasks were also refrigerated. After 7 days, the tubes not stored in desorption solution were desorbed and all samples were analyzed for S(IV), sorbent samples analyzed according to ref 22 and buffered formaldehyde analyzed as described in ref 14.
RESULTS AND DISCUSSION As hydrolysis of S02(g) is the initial step of the stabilization reaction, water must be present on the sorbent. To ensure favorable equilibrium and kinetics of reaction 1, p H on the sorbent must also be correct.
S(IV)(aq) + RCHO + RCH(OH)SO,-
(1)
Optimum p H for formaldehyde stabilization is 4-5 (14). When ethanedial is used as stabilizer instead of formaldehyde, p H optimum should not be much different due to the similarity in reactivity of the aldehydes. Choice of Solid Carrier. Catalytic considerations call for a synthetic and homogeneous carrier for sampling of sulfur dioxide, as the surface activity of natural sorbents such as
1332
ANALYTICAL CHEMISTRY, VOL. 57, NO. 7, JUNE 1985
Table I. Carrier/Stabilizer Combinations Tested carriern
stabilizer
XAD-2
XAD-7
charcoal
benzaldehyde 3-phenylpropenal formaldehyde acetaldehyde acetone glyceraldehyde dihydroxyacetone glycerol ethanedial
RD, OX RD, OX
RD, OX RD, OX
RD, OX RD, OX
5A
LR
ox
silica
HMDS
IRC-84
LR LR
LR, OX
ox ox ox ox ox
LR, OX
ox
GOOD
Key: XAD-2, XAD-7, and IRC-84 are Amberlite products. IRC-84 was partly regenerated. 5A = 5A molecular sieves. Silica, silica gel; HMDS, silica gel silylated with hexamethyldisilazan;RD, rapid drying; OX, oxidation of more than 20% of the S(1V)to S(V1);LR, total recovery of S(1V)and S(V1) less than 80% of SOz(g)applied. See Experimental Section for details on preparation and testing.
I
I
0
mm
2
I
I
6 Volume sampled (dm31 4
I
'
8
Flgure 1. Distribution of S(IV) on the tube after sampling of SO,(g) for 15 min at different relative humidities: pump, SKC Model 222-3 at 200 mL/min; test atmosphere, 5 mg of S0,(g)/m3; 20 OC.
Figure 2. Breakthrough volume when different concentrations of ethanedial are used for swelling the dry resin. The ratio of stabilizer solution/dry carrier was 1:l (vlw) in all cases. Test atmosphere was 5 mg of S0,(g)lm3, 10% RH, and 20 OC. Stabilizer solutions were as follows: (0)2, 4, and 6 M ethanedial (from right to left); (A)water.
charcoal is known to catalyze the oxidation of sulfur dioxide to sulfate (24). Our search for a solid carrier started with the styrene-divinylbenzene copolymer Amberlite XAD-2. The absence of hydrophilic, water-retaining groups on the surface made water dry away rapidly from this carrier, causing low breakthrough volumes. The best carrier for our purpose would thus be one with high polarity. After testing a number of different materials, we found that a partly regenerated weak cation exchange resin would be the ideal carrier for our purpose. We selected Amberlite IRC-84, which is a poly(acry1ic acid) gel, that has both higher polarity and a lower dissociation constant than the more common poly(methacry1ic acid) based weak cation exchangers. The apparent pK, is 5.3, and the concentration of active groups is approximately 4 M. We had thus found both a highly polar carrier and an "anion-free" buffer of very high capacity at the desired pH. Choice of Stabilizer Aldehyde. Low volatility is a key feature for a reagent on a solid sorbent, as most of the sampled material is trapped in the foremost part of the tube (Figure 1). This is also the part of the sorbent that will be first deprived of the stabilizer if a volatile compound is used. High stability toward air oxidation and solubility in water are also essential features for the aldehyde of choice. Formaldehyde conforms only to the last of these specifications, so another aldehyde had to be used. Our choice fell on ethanedial, as both the compound itself and its only air oxidative degradation product (25,26),oxoethanoic acid, are aldehydes with reactivities comparable to that of formaldehyde (27). Hydrate formation and oligomerization of ethanedial in aqueous solution (28) contribute to the decrease in its vapor pressure and give the sorbent ad-
ditional water-retaining capacity. Ethanedial also has some advantages in the determination step, as compared to formaldehyde (22). Sorbent Retaining Wad. Materials commonly used are glass wool and polyurethane foam (29), which both caused oxidation of SO,(g) to sulfate. Glass wool also gave a low total sulfur recovery. Raw and trimethylsilylated quartz wool were tested but gave problems similar to those with glass wool. P T F E wool was the only tested material that did not cause oxidation or decrease in recovery and was therefore used. Breakthrough Tests. A breakthrough of sulfur dioxide will occur when the sorbent is exhausted on the water that was added as part of the stabilizer solution. Low relative humidity and high temperature will therefore decrease the maximum permittable sample volume. The concentration profile seen at high humidity conditions requires a high ethanedial concentration to ensure stabilization. As water is displaced by increasing the ethanedial concentration in the stabilizer solution, a higher degree of stabilization can only be obtained at the cost of a lower breakthrough volume (Figure 2). We settled for a 2 M solution, which will ensure a reagent excess of at least 10 times, even when sampling 3 dm3 air with an SOz(g)concentration 10 times the TLV and assuming a local concentration buildup in the front end of 10 times that of a rectangular distribution of the sample along the sorbent tube. This concentration of ethanedial does not impair the breakthrough volume of the sorbent, as compared to using water only. Results from the storage tests below also show that the degree of stabilization obtained using this concentration is sufficient. A 1:l (v/w) 2 M ethanediddry carrier ratio was the highest stabilizer loading that could be handled without difficulty.
downstream
X
ANALYTICAL CHEMISTRY, VOL. 57, NO. 7,JUNE 1985
1333
Table 11. S(1V) Recovery at Different S02(g) Levelsn % recovery of S(1V) after storage in refrigerator room temp, light
SOz(g)concn, mg/m3
97 f 1.9 93 i 1.4 102 f 4.2
1
5 25
79 f 2.4
81 f 2.1 87 i 3.1
"Test atmosphere with 50% RH was sampled for 15 min at 200 mL/min. Samples were stored on the tubes for 8 days between sampling and analysis. Values given are means of three to five determinations with standard errors (95% confidence interval). I
I
I
I
I
5
0
10 15 Volume sampled (dm3)
'
20
Table 111. S(1V) Recovery after Storage of Sorbent in Desorption Solution"
F
5 2
% of SOz applied recovered as
days after sampling and desorption
100-
50-
S(1V) after storage in refrigerator room temp, light
7
100.2 i 0.6
99.0 f 0.4
25
100.0 i 0.8
98.0 f 0.7
9*
98.1 f 0.9
" Desorption was started immediately after sampling and lasted
ap
for 8 days. Values given are means of three to five determinations with standard errors (95% confidence interval. Samples were desorbed in water. Sample was desorbed in 3.5 mM NaHC03.
*
0-
0
20
10
30
40
50
Volume sampled (dm3)
@
0
*r
1
A
1
1
,
0
8
1
1
I
2
4
7
l4
Days stored between sampling and determination
16
8 12 vokme sampled (dm31 Figure 3. Breakthrough volumes at different temperatures and relative humidities of the test atmosphere: 200 mg of adsorbent with a 2 M ethanedial/dry carrier ratio of 1:l (v/w) was used; test atmosphere, 5 mg of S0,(g)/m3. (A) Temperature, 20 OC;relatlve humidity, 10, 30, and 50% RH, respectively, from left to right. (B) Temperature, +4 O C ; (A)10% RH; (0)50% RH. (C)Temperature, 38 OC;(A)10% RH; (0)50% RH. 4
With this we ran a number of tests to determine the maximum sample volume at various temperature and relative humidities. Figure 3 shows the results of these experiments. At room temperature and medium relative humidities, samples of considerable volumes could be taken, whereas the breakthrough volume of the sorbent was limited when sampling at low relative humidities and high temperatures. In regular use, the tube should be supplied with a separate backup section downstream of the analytical section. The sorbent changes from opaque to transparent when drying. This can be used to provide a visible warning if breakthrough is about to or has occurred. Distribution of Sampled S 0 2 ( g )on the Tube. While Figure 1 provides an illustrative picture of the variation in distribution of sampled gas along the tube when used for sampling from atmospheres of different relative humidity, the semiquantitative approach used in these experiments should be kept in mind when interpreting the results.
Flgure 4. Effect of storage between sampling and analysis on recovery of sulfur dioxide as S(IV): open symbols, samples stored in a refrigerator at +4 O C ; filled symbols, stored at 20 OC under fluorescent light; % RH during sampling, (0)5% RH, (0) 50% RH, (A)95% RH.
Storage Tests. Tests were restricted to concentrations five times above and below the current Swedish TLV. Relative humidity was included as a parameter in our storage test, as % RH at the sampling site may vary considerably and thereby affect the postsampling storability of the tubes due to difference in spatial distribution of S02(g)on the tube, as shown above. The tubes were stored for up to 2 weeks between sampling and determination. Results are presented in Table I1 and Figure 4. In samples stored at room temperature under fluorescent light, a significant decay in recovery is evident, especially for samples taken a t high relative humidity. The recovery can, however, be increased by starting the desorption as fast as possible after sampling (Table 111),as all the stabilizing aldehyde of the sorbent will be made available to the sample. This is the recommended procedure for samples taken under high relative humidity conditions and samples that are to be stored for extensive time between sampling and determination. When ion chromatography was used in the determination, the sorbent was desorbed in 3.5 mM NaHC03 to minimize the "carbonate dip" (30). We checked the stability of the sample in this solution and found it satisfactory.
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 7, JUNE 1985
Table IV. Effect of Desorption Time on Recoverya desorption time 5 min 15 min
8 1 i 1.2 96.3 i 0.8 99.6 i 1.0 100.1 f 0.6 90 i 1.1
l h 5h 5
recovery as S(1V) in % of SOz(g)applied
minb
Em-
5 lo-
'Tubes were stored in a refrigerator 24 h between sampling and desorption. Values given are means of three to five determinations with standard errors (95% confidence interval). Desorption vials were agitated by two inversions during the desorption time. Treated in an ultrasonic bath.
5I
A test to determine the presampling storability of the sorbent tubes was also included in the storage tests. Eight tubes packed with new sorbent gave, after storage for up to 2 weeks after sampling, recoveries that were 2.8 f 4.8% (mean f standard error; 95% confidence interval) higher than those obtained with the old sorbent. The stabilizing power of the sorbent has thus not been affected by storage for 4 months prior to use. Desorption Time. The ion exchange resin used as carrier is of a gel type, which allows the sampled species to diffuse into it after sampling. Diffusion in the polymeric carrier is rather slow due to the cross linking, and a minimum desorption time of l h must therefore be used to ensure quantitative desorption (Table IV). Some agitation should be applied to avoid buildup of high sample concentration in the carrier sediment as this will retard the desorption process. Ultrasonic treatment did not increase the speed of desorption much and is not recommended because it necessitates filtration of the sample from fine carrier particles produced by the treatment. Determination. A modified pararosaniline colorimetric method (22) is recommended for routine use. Typical sensitivity for a sample taken for 15 min a t 200 mL/min from an atmosphere containing 5 mg of S02/m3was 1absorbance unit. Detection limit was 20 pg/m3. The blank from the sorbent tube did not differ from that seen from the same amount of ethanedial dissolved in water, which in turn was practically equal to that seen with deionized water only. Comparative Field Study. Field performance was tested and compared to the method of Dasgupta et al. (14) in a sulfite paper pulping plant. The numerical results are compiled in
I
I
lo
5
I
I
20
50
J
Flgure 5. Concentrations found with solid sorbent and buffered formaldehyde impinger method. Concentrations are given in mg of SO2(g)/m3. Samples were stored for 7 days between sampling and analysis: (A)desorbed dlrectly and stored in a refrigerator; (W) stored on the tube in a refrigerator; (+) stored on the tube at 20 OC under fluorescent light.
Table V and visualized in Figure 5 as a plot of the results obtained with the sorbent tubes vs. those obtained with the buffered formaldehyde impinger method. Standard deviations for the differences between duplicate runs within each sampling method were calculated and tested for difference by the = 2.98 at 95% F-test. The test gave an F value of 49.5 (Flo,lo confidence level). The precision obtained with the sorbent tubes was thus significantly better than that of the impingers, through which it was difficult to maintain a constant flow with the equipment used. Other Uses of the Solid Buffer. The partly regenerated ion exchanger used as solid buffer for the sorbent described in this paper could be useful on other solid sorbents for sampling of various compounds from air in occupational hygiene. Choice of buffering carrier is not restricted to the poly(acry1ic acid) used here. When buffering in another pH range is desired, there are several other ion exchangers that can come to use. These could be regular weak cation or anion exchangers of the poly(methacry1ic acid) and amino type or more specialized types with functional groups like iminodiacetic acid (Chelex loo), phosphonic acid (31), or aminophosphonic acid (Duolite ES-467), just to mention a few. For
Table V. Results from the Field Test sample no. 1 2 3 4 5 6 7
8 9
10 11
storagea DD DD DD RE
RE RE RT RT RT RT RT
concentrations found (mg S0,(g)/m3) by impinger 1 impinger 2 sorbent 1 sorbent 2 6.7 11.1 62.1 4.4 4.7 12.9 5.0 5.5 5.3 9.2 57.6
7.0 10.9 55.9 4.6 4.1 11.9 5.2 5.4 5.4 9.0 50.2
7.7 12.0 64.4 4.3 4.2 12.9 4.3 5.4
6.3 8.9 52.8
7.8 11.9 63.6 4.3 4.1 13.0 4.4 5.1 5.4 8.3 52.1
differenceb impinger sorbent -0.3 0.2 6.2 -0.2 0.6 1.0 -0.2 0.1 -0.1 0.2 7.4
-0.1 0.1 0.8
fO 0.1 -0.1
-0.1 0.3 0.9 0.6
0.7
Statistics for the Differences impinger sorbent
1.35 i 2.73 0.29 f 0.39
F=
(2.73/0.39)'
= 49.5
Samples were stored 7 days between sampling and determination. aDD, desorbed directly after sampling and stored in a refrigerator; RE,tube stored in a refrigerator; RT,tube stored at room temperature under fluorescent light. bDifference between channel 1and 2 for each method.
Anal. Chem. 1985, 57, 1335-1338
special purposes, the possibility of synthesizing special groups on neutral polymers or chemically modifying existing groups could be considered (32). In some cases, direct use of functionalized polymers as stabilizers might be feasible. During early stages of this work we considered reducing parts of the carboxylic acid groups of Amberlite IRC-84 to aldehyde, thus eliminating the need for a separate stabilization reagent. The idea was never tested, as we found a simpler solution to the problem in the sorbent presented here. ACKNOWLEDGMENT We thank Anders Cedergren for valuable help and Michael Sharp for linguistic revision of the manuscript. Registry No. SOz, 7446-09-5;Amberlite XAD-2, 9060-05-3; Amberlite XAD-7, 37380-43-1; Amberlite IRC-84, 11098-83-2; benzaldehyde, 100-52-7;3-phenylpropenal,104-55-2;formaldehyde, 50-00-0;acetaldehyde, 75-07-0;acetone, 67-64-1;glyceraldehyde, 367-47-5;dihydroxyacetone,96-26-4; glycerol, 56-81-5; ethanedial, 107-22-2. LITERATURE C I T E D (1) von Nieding, G.; Wagner, H. M. Atemw.-Lungenkrkh. 1982, 8 ,
190- 193. (2) von Nieding, G. EHP, Envlron. Health Perspecf. 1978, 2 2 , 91-92. (3) Nordenson, I.; Beckman, G.; Beckman, L.; Rosenhall, L.; Stjernberg, N. Hereditas 1980, 9 3 , 161-164. (4) Anderson, C. C.; Gunderson, E. C.; Coulson, D. M. I n "Chemical Hazards in the Workplace"; Choudhary, G., Ed.; American Chemical Society: Washington, DC, 1981; ACS Symp. Ser. 149, pp 3-19. (5) Huygen, C. Anal. Chlm. Acta 1963, 2 8 , 349-360. (6) Eller, P. M.; Kraus, M. "NIOSH Manual of Analytical Methods"; NIOSH: Cincinatti, OH; Vol. 7, Method no. P&CAM 268. (7) Takamine, K.; Tanaka, S.;Hashimoto, Y. Bunsekl Kagaku 1982, 3 1 , 692-96. (8) Klockow, D.; Teckentrup, A. I n t . J . Envlron. Anal. Chem. 1980, 8 , 137- 148.
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(9) Chriswell, C. D.; Gjerde, D. T. Anal. Chem. 1982, 5 4 , 1911-1913.
(IO) Vinjamoori, D. V.; Ling, C.4. Anal. Chem. 1981, 5 3 , 1689-1691. (11) Smith, D. L.; Kim, W.S.;Kupel, R. E. Am. Ind. Hyg. Assoc. J . 1980, 4 1 485-488. (12) Black, M. S.;Herbst, R. P.; Hitchcock, D. R. Anal. Chem. 1978, 5 0 , 848-851. (13) Reiszner, K. D.; West, P. W. Env. Sci. Technol 1973, 7,526-532. (14) Dasgupta, P. K.; DeCesare, K.; Ullrey, J. C. Anal. Chem. 1980, 5 2 , 1912-1922. (15) Dasgupta, P. K.; DeCesare, K. B. Afmos. Environ. 1982, 16, 2927-2934. (16) Lindgren, M.; Cedergren, A.; Lindberg, J. Anal. Chlm. Acta 1982, 14 1 , 279-286. (17) West, P. W.; Gaeke, G. C. Anal. Chem. 1956, 28, 1816-1819. (18) Scaringelli, F. P.; Saltzman, B. E.; Frey, S.A. Anal. Chem. 1967, 3 9 , 1709-1 7 19. (19) O'Keeffe, A. E.; Ortman, G. C. Anal. Chem. 1966, 3 8 , 760-763. (20) Cedergren, A.; Wikby, A.; Bergner, K. Anal. Chem. 1975, 47, 100-1 06. (21) Irgum, K. Anal. Chem. 1983, 55, 1186-1187. (22) Irgum, K. Anal. Chem. 1985, 5 7 , 1335-1338. (23) Irgum, K. Anal. Chem. 1985, 57, 1496-1498. (24) Nishijima, A.; Hagiwara, H.; Kurita, M.; Ueno, A,; Sato, T.; Kiyozumi, Y.; Todo, N. Bull. Chem. Soc Jpn. 1982, 55, 2618-2621. (25) Neuberg, C.; Kobel, M. Biochem. 2. 1932, 256, 475-484. Chem. Abstr. 1933, 2 7 , 1618. (26) Neuberg, C.; Kobel, M. Naturwissenschaften 1932, 16, 953-954. (27) Fieser, L. F.; Fieser, M. "Advanced Organic Chemistry"; Van Nostrand: New York, 1961; pp 443-444. (28) Whipple, E. B. J . Am. Chem. SOC. 1970, 9 2 , 7183-7186. (29) "1982 Catalog and Guide to Air Sampling Standards"; SKC Corp.: Eighty-Four, PA, 1962; p 13. (30) Stevens, T. S.; Davis, J. C ; Small, H. Anal. Chem. 1981, 5 3 , 1488-1 492. (31) Helfferich, F. "Ion Exchange"; McGraw-Hill: New York, 1962; pp 38-39. (32) Frechet, J. M. J.; Farrall, M. J. I n "Chemistry and Properties of Crosslinked Polymers"; Labana, S. s., Ed.; Academic: New York, 1977; pp 59-83. I
RECEIVED for review July 17, 1984. Resubmitted January 22, 1985. Accepted January 22,1985. Grants from the Stiftelsen Bengt Lundqvists Minne are gratefully acknowledged.
Pararosaniline Colorimetric Determination of Sulfur Dioxide Stabilized with Ethanedial Knut Irgum
Department of Analytical Chemistry, University of U m e i , S-901 87 U m e i , Sweden
A hydroxide-consuming intra-Cannirzaro reaction of ethanedial desorbed from the solid sorbent occurs during the hydrolysis step preceding the color reaction. A higher initial OHconcentration is therefore needed In the hydrolysis, as compared to methods without ethanedlal in the sample. Hydrolysis time should be kept between 10 s and 5 min for maximum sensitivity. Optlmum pH and formaldehyde concentration during color development were 1.02 and 5 mM, respectively. The alkaline formaldehyde solution containing 0.5 M NaOH and 20 mM formaldehyde was stable for 1 day at room temperature.
A solid sorbent for sampling sulfur dioxide in occupational hygiene has recently been developed in our laboratory (1). The gas is stabilized as an addition compound with ethanedial a t p H 5 after initial hydrolysis. HSO8- + OHCCHO + OHCCH(OH)SO,(1) Dasgupta e t al. (2) have shown that a modified pararosaniline colorimetric method can be used for determination of S02(g)sampled with buffered formaldehyde solution if the
sample is subjected to an alkaline hydrolysis prior to the color reaction. When this method was applied to samples taken with the solid sorbent, some complications were seen. A discussion of these is presented here and the reaction is optimized for use with ethanedial-containing samples. EXPERIMENTAL S E C T I O N Reagents and Solutions. Apart from the purified (3) pararosaniline ("standard grade"; Fluka, Buchs, Switzerland) and the 6 M aqueous ethanedial (synth.;Merck-Schuchardt,Hohenbrunn, FRG), all chemicals were reagent grade. The formaldehyde was used without removing the 10% methanol that was added as polymerization inhibitor. Acetate-buffered hydroxymethanesulfonate (HMS) ( 4 ) was diluted to 25 pM in 50 mM ethanedial and used as test sample. The alkaline formaldehyde solution was composed of 20 mM formaldehyde in 0.5 M NaOH and the pararosaniline color reagent contained 0.8 mM pararosaniline hydrochloride in 1.00 M HCl. These are the optimized reagents, which were used if not otherwise noted. General Procedure. A 1.5-mL sample was hydrolyzed with 0.75 mL of alkaline formaldehyde for 15 s. The hydrolysate was thereafter added to 0.75 mL of the color reagent. Gilson adjustable air displacement pipets were used to ensure instant mixing of the solutions. After 10 min the absorbance at 580 nm was measured
0003-2700/85/0357-1335$01.50/00 1985 American Chemical Society
