Anal. Chem. 1985, 57, 1583-1586
and in the aquatic environment.
ACKNOWLEDGMENT We thank H. Monch, C. Schaffner, M. Tschui, and Y. Zelikovitz for technical assitance and P. Brunner, T. Conrad, and J. McEvoy for helpful discussions. We thank H. Bolliger for drafting the figures and B. Hauser for typing the manuscript. We acknowledge K. and G. Grob for supplying glass capillary columns for high-resolution gas chromatography. Registry No. NP, 104-40-5; NPlEO, 104-35-8; NPPEO, 20427-84-3; HzO, 7732-18-5. LITERATURE CITED Haupt, D. E. Tenside Deterg. 1083, 20, 332-337. Kravetz, L. J . Am. 0llChem. SOC. 1081, 56, 58A-MA. Giger, W.; Stephanou, E.; Schaffner, C. Chemosphere 1081, 70,
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(8) Reinhard, M.; Goodman, N.: Mortelmans, K. E. Environ. S d . Techno/. 1082, 76,351-362. (9) Garrison, A. W.; HIII, D. W. Am. Dyest. Rep. 1072, February. (10) Giger, W.; Brunner, P. H.; Schaffner, C. Science (Washington, D.C.) f084s 225, 623-625. (11) McLeese, D. W.; Zitko, V.; Metcaife, C. D.; Sergeant, D. B. Chemosphere 1080, 9, 79-82. (12) Brlngmann, G.; Kiihn, R. 2. WaswfAbwassefForsch. 1082, 75, 1-6. (13) "Analytlcal Methods Manual"; Inland Waters Dlrectorate: Ottawa, Canada, 1980. (14) Glger. W.; Ahel, M.; Schaffner, C. I n "Analysis of Organic Water
Pollutants"; Angeletti, G., Bj~rseth,A., Eds.; Reidel: Dordrecht, Holland, 1984, pp 91-109 (15) Veith. G. P.; Kiwus, L. M. Bull. Environ. Contam. Toxicol. 1077, 77, 831-636. (16) Grob, K.; Grob, G.; Blum, W.; Walther, W. J . Chromatogr. 1082, 244, 197-208. (17) Wickbold, R. Tenside Deterg. 1972, 9, 173-177. (18) Ahel, M.; Giger, submitted for publication in Anal. Chem. (19) Gerhardt, W.; Much, H. Tenside Deterg. 1081, 78, 120-123.
1253-1 263.
Stephanou, E.; Giger, w. EflVkOfl. SCi. f8ChflOl. 1082, f 6 , 800-805. Bruschweller, H.; Glimperle, H.; Schwager, F. Tens& Deterg. 1083, 20, 317-324. Ahel, M.; Giger, W.; Molnar-Kubica, E.; Schaffner, C. I n "Analysis of Organic Water Pollutants"; Angelettl. G., BJDrseth, A., Eds.; Reidel: Dordrecht. Holland; 1984, pp 280-288. Sheldon, L. S.; Hites, R. A. Sci. Total Environ. 1070, 7 7 , 279-286.
RECEIVED for review November 13, 1984. Accepted February 11, 1985. This project was supported in part by the Swiss National Science Foundation (Nationales Forschungsproin 7D, research project on Sewage Sludge").
Determination of Aldehydes and Acetone by Ion Chromatography Dean L. DuVal, Margaret Rogers, and James 5.Fritz* Ames Laboratory and Department of Chemistry, Iowa State University, Ames, Iowa 50011
Low molecular welght aldehydes and acetone in aqueous samples are determlned by slngie-column ion chromatography. The aldehydes and acetone are derlvatlzed to a-hydroxyalkanesuifonates using sodlum bisulfite and the sulfonates that are formed are then separated by ion chromatography and detected by uslng a conductivity detector. Ionic specles that can Interfere with chromatographlng of the aidehydes and acetone are removed from the sample before the aldehydes and acetone are derlvatlzed. Llnear callbration curves are also reported for the derlvatired specles.
Low molecular weight aldehydes are found in a wide variety of samples. They are of increasing environmental concern because of their adverse effects on health. Quantitative analytical procedures for measuring large amounts of aldehydes (oximation, etc.) and for measuring aldehyde and acetone concentrations in organic samples (gas and liquid chromatography) generally cannot be used for aqueous samples which contain only trace amounts of the aldehydes and ketones. Resin concentration procedures (1)or purge-and-trap methods (2) usually fail for dilute aqueous samples or give low recoveries because the smaller aliphatic aldehydes and methyl ketones, although volatile, have high water solubilities. Samuelson (3) and several other investigators have reported that aldehydes and some methyl ketones are retained by an anion-exchange column in the bisulfite form. The aldehydes and methyl ketones react with the bisulfite to form ionic a-hydroxyalkanesulfonatesat the exchange site. In the present work, the first three members of the aliphatic aldehyde homologous series plus acetone are determined by conversion to the a-hydroxyalkanesulfonatesand then separated and measured by ion chromatography. This method is simple and appears to be quite selective. Good quantitative 0003-2700/85/0357-1583$01.50/0
results are obtained on aqueous samples containing only a few parts per million of formaldehyde, acetaldehyde, acetone, and propionaldehyde.
EXPERIMENTAL SECTION Equipment, A homebuilt HPLC was used containing a Model 213A conductivity detector made by Wescan Instruments (Santa Clara, CA) with a measured cell constant of 33 cm-'. The chromatograph contained a LKB/BROMMA Model 2150 dud-piston pump to provide eluent flow. A Rheodyne (Berkeley, CA) Model 7010 injection valve fitted with a 50-pL sample loop was used for sample introduction. Thermal stability of the system was maintained with an Eldex (San Carlos, CA) column oven and other appropriate insulation. The analytical column used was a resin based anion exchange column (250 X 4 mm) from Wescan Instruments (Santa Clara, CA). Dowex 1x8, a high-capacity anion exchange resin in the acetate form, ws used in the anion interference study. The resin waa slurry packed in a gravity-flow glass column (100 X 10 mm). Solutions. The eluent used was 20 mM citric acid prepared from the reagent grade solid and distilled, deionized water. The pH of the eluent was approximately 2.6 and was not adjusted. All analytical solution were also prepgred from the highest grade materials available and distilled, deionized water. Aldehyde, ketone, and sodium bisulfite stock solutions were prepared weekly. Mixtures of bisulfite and the aldehydes were allowed to equilibrate for approximately 3 h before injection except during the time-dependent studies on the formaldehyde-bisulfite reaction. Calibration and Interference Studies. Standards for calibration curves were prepared by appropriate dilution of aldehyde or acetone stock solutions, addition of a specific excess amount of bisulfite stock solution (five times the molar concentration of the most concentrated aldehyde or ketone standard), dilution, and mixing. After a given length of time (3 h except for the time reaction) the samples were injected into an ion chromatograph. Reaction interference studies were done by adding the interferent (acetone) at the same time the formaldehyde and sodium 0 1985 American Chemical Soclety
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 8, JULY 1985
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20
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10
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8 -
64-
201
1 1
21
31
41 51 61 71 Molar Ratio (HSO- Formaldehyde)
81
91
101
Flgure 1. Plot of the peak height of 10 ppm formaldehyde vs. the molar ratio of bisulfite to formaldehyde.
bisulfite were added together in the volumetric flask. Chromatographic interference studies were done by adding the excess chloride to the aldehyde solutions before they were passed through an anion exchange column in the acetate form. The effluent was collected in a volumetric flask containing sodium bisulfite. A flow rate of approximately 3.5 mL/min was used for chromatographic separations.
RESULTS AND DISCUSSION Chromatographic Conditions. Most of the preliminary work was performed on solutions of the bisulfite addition product of formaldehyde and acetaldehyde. These solutions also contained excess sodium bisulfite. Several combinations of chromatographic eluents and eluent pHs were tried with varying degrees of success. In most instances the formaldehyde peak was good while the peak for acetaldehyde was rather broad. Previous work ( 4 ) has demonstrated that the bisulfite addition product is most stable at a pH of about 3. Recent research in ion chromatography has shown that several carboxylic acid eluents provide excellent sensitivity for anion chromatography using a conductivity detector (5). Therefore, citric acid was tried as an eluent and was found to be excellent for separating the bisulfite addition products (a-hydroxyalkanesulfonates) of the lower molecular weight aldehydes and acetone. The excess bisulfite elutes very late under these conditions and does not interfere with the chromatogram. Reaction Conditions. For quantitative work, it is essential that the carbonyl compound react quantitatively, or at least reproducibly, with sodium bisulfite in dilute solutions. Figure 1 shows that if sufficient time is allowed for the reactioe (3 h ws used), the peak height of the formaldehyde addition product is constant at a bisulfite to formaldehyde mole ratio of 2 or higher. The results of a reaction-time study given in Figure 2 show that approximately 3 h of reaction time is required for a constant peak height if a bisulfite-aldehyde mole ratio of 2 is used. However, a t mole ratios of 5 or 10, a much shorter reaction time is required to obtain a constant peak height. A %fold molar excess of bisulfite was used throughout this study to minimize the base line disturbance caused by the bisulfite eluting later from the chromatographic column in a broad band. No significant change in retention times caused by bisulfite was observed during a full day of injections (21 samples). However, the chromatographic system was usually run at a low flow rate overnight to make sure that the bisulfite was completely removed from the column before new samples were run on the following day.
0-
I
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50
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100
I
150
I
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200
250
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Flgure 2. Plot of peak height of 20 ppm formaldehyde vs. reaction time using 2-, 5-,and 10-fold molar excesses of sodium bisulfite. The 2-fold excess curve is plotted with triangles, the 5-fold excess is plotted with solld squares, and the 10-fold excess is plotted with open squares.
Table I. Retention Time of Common Anions and the Aldehyde and Methyl Ketone Derivatives" anion
retention time, min
phosphate formaldehyde derivative chloride acetaldehyde derivative methanesulfonate acetone derivative ethanesulfonate nitrate propionaldehyde derivative
1.06 2.13 2.42 2.64 2.86 3.44 5.27 6.11 6.50
Conditions used were the same as those given in Figure 3.
Scope. It was found that a mixture of the bisulfite addition products of formaldehyde, acetaldehyde, propionaldehyde, and acetone could be nicely separated by ion chromatography (Figure 3). In addition to this separation of the a-hydroxyalkanesulfonates, a separation of methane-, ethane-, and propanesulfonate could also be accomplished. Table I shows similar retention times for the alkanesulfonates and the corresponding a-hydroxyalkanesulfonates. Table I also shows that, of the common inorganic anions, only chloride has a retention time similar to most of the a-hydroxyalkanesulfonates.Thus, a large excess of chloride would likely interfere with the determinations of these low molecular weight carbonyl compounds. This is confirmed by the chromatogram in Figure 4A. An interfering anion such as chloride can be removed by ion exchange before the aldehydes and ketones are converted to ionic species. This can be accomplished by passing the sample through a small anion-exchange column in the acetate form. Chloride and other anions in the sample are exchanged for acetate. When the sample has been reacted with sodium bisulfite and injected into the chromatographic column, the acidic pH of the eluent (approximately 2.6) converts most of the acetate into nonconducting molecular acetic acid. Figure 4B shows that a sample containing formaldehyde, acetaldehyde, and chloride treated this way gives essentially the same chromatogram as a same sample that initially contained no chloride (Figure 4C). The shoulders on the formaldehyde and acetaldehyde peaks are caused by column deterioration. Since an excess of bisulfite must be used to ensure complete conversion of a carbonyl compound to the a-hydroxyalkane-
ANALYTICAL CHEMISTRY, VOL. 57, NO. 8, JULY 1985
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L I
l
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I
I
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Flgure 3. Chromatogram of 25 ppm formaldehyde, 50 ppm acetaldehyde, 100 ppm acetone, and 100 ppm propionaldehyde Using 20 mM citric acid at a flow rate of 3.5 mL/mln.
sulfonate, each sample will also contain bisulfite, or perhaps some sulfate. Both bisulfite and sulfate are strongly retained by the chromatographic column and do not interfere with the determination of the earlier-eluting hydroxysulfonates. However, after many injections the late eluting bisulfite might occupy enough of the exchange sites to affect the separation. If this problem occurs, the bisulfite could be cleaned off the column by injection of a concentrated solution of citrate. This only needs to be done if the retention times of the a-hydroxyalkanesulfonates decrease significantly. If a minimum excess of bisulfite is added to each sample, buildup of bisulfiite on the analytical column is not a problem. However, the bisulfite will eventually elute from the column and may cause some base line perturbations. Quantitation. With 20 mM citric acid eluent at a flow rate of 3.5 mL/min and a conductivity detector, linear calibration curves were obtained for formaldehyde (0-25 ppm), acetaldehyde (0-75 ppm), propionaldehyde (0-250 ppm), and acetone (0-100 ppm). It should be possible to extend the upper values without dilution and to analyze samples accurately in the lower end of these limits by increasing the sensitivity setting of the detector. The linear regression equations for y = mx + b, where y is the peak height in centimeters and x is the concentration in parts per million, were as follows: formaldehyde, m = 0.8901, b = -0.0748, correlation = 0.9998; acetaldehyde, m = 0.1683, b = 0.0095, correlation = 0.9997; propionaldehyde,m = 0.0643, b = 0.1990, correlation = 0.9997; acetone, m = 0.0701, b = -0.0119, correlation = 0,9999. Aqueous standards and samples containing aldehydes and acetone must be handled carefully to avoid loss due to volatility. The sample containing the three aldehydes plus acetone separated in Figure 3 was allowed to stand in an open beaker for 4 h before chromatographing a second time. The three aldehyde peaks showed little change, but the acetone peak was reduced to approximately one-third of its former peak height. This is a consequence of the greater dissociation constant of the acetone-bisulfite addition product (k = 4 X compared to dissociation constant of the formaldehyde
0
3
6
9
12 15 18
mrnutes
Figure 4. Chromatograms of 25 ppm formaldehyde and 40 ppm acetaldehyde using conditions the same as those given in Figure 3. Chromatogram A also has 1000 ppm GI-. Chromatogram B had 1090 ppm CI- but was passed through an ion exchange column in the acetate form to remove the CI- before the aldehydes were derivatized. Chromatogram C contains only the aldehydes.
( K = 1.2 X lo-‘) or acetaldehyde addition product (12 = 2.5 X lo4). Thus, samples containing acetone should be stoppered and chromatographed without undue delay. Preconcentration. Samuelson (3) reported that aldehydes and methyl ketones could be retained on high-capacity anion exchange resins in the bisulfite form. Therefore, attempts were made to preconcentrate aldehydes on a low-capacity column of a type commonly used in ion chromatography. However, preliminary work indicates that the low molecular weight aldehydes and acetone cannot be quantitative concentrated on the preconcentrator column in the bisulfite form. If the aldehydes could have been collected on the preconcentrator column, an automated analysis would have been possible. It seems likely that a longer reaction time is needed than that provided by the anion-exchange precolumn. An alternative preconcentration method is currently under investigation.
ACKNOWLEDGMENT We thank Wescan Instruments for a gift of the resin-based anion exchange column used in this work. Registry No. Formaldehyde, 50-00-0; acetaldehyde, 75-07-0; acetone, 67-64-1;propionaldehyde, 123-38-6;phosphate, 1426544-2; chloride, 16887-00-6;methanesulfonate, 16053-58-0; ethanesulfonate, 10047-83-3;nitrate, 14797-55-8. LITERATURE CITED (1) Chang, R. C. PhD. Dissertation, Iowa State University, Ames. IA, 1976. (2) Spraggins, R. L.; Oidham, R. 0.; Prescott, C. L.; Baughman, R. J. In “Advances in the Identification and Analysis of Organic Pollutants in Water”; Keith, L. H., Ed.; Ann Arbor Science: Ann Arbor, MI, 1981; Vol. 2, Chapter 41. (3) Samueison, 0.”Ion Exchangers in Analytical Chemistry”; Wiley: New York, 1953; Chapter 16.
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(4) Kokhoff, I. M.;Stenger V. A. "Volumetric Analysis"; Wlley: New York, 1957; Vol. 3, p 384. (5) Fritz, J. S.; DuVal, D. L.; Barron, R. E. Anal. Cbem. 1984, 56, 1177.
RECEIVED for review January 10,1985. Accepted March 22,
1985. Ames Laboratory is operated for the U.S. Department Energy under Contract No. W-7405-ENG-84. This work was supported by the Director of Energy Research, Office of Basic Energy Sciences. Of
Determination of Sulfur Dioxide, Nitrogen Oxides, and Carbon Dioxide in Emissions from Electric Utility Plants by Alkaline Permanganate Sampling and Ion Chromatography John H. Margeson,* Joseph E.Knoll, a n d M. Rodney Midgett Environmental Monitoring Systems Laboratory, US.Environmental Protection Agency, Research Triangle Park, North Carolina 27711 Guy B. Oldaker, 111, and Wayne E. Reynolds Entropy Environmentalists, Inc., Post Office Box 12291, Research Triangle Park, North Carolina 27709
A manual 24-h integrated method for determlnlng SO,, NO,, and CO, In emlsslons from electric utlllty plants was developed and fleld tested downstream from an SO, control system. Samples were collected In alkallne potasslum permanganate solution Contained In restrlcted-orlflce Implngers. SO, Is oxldlzed to SO-: and S202-, and NO, (NO NO2) is oxldlzed to NO,-; CO, Is converted to C03,-. Samples were analyzed by Ion chromatography. The method showed 100 % collectlon efficiency for all three pollutants at a sample flow rate of 35 cma/mln and was found to be unbiased relative to Independent monltorlng systems. At a flow rate of 75 cm3/ mln, the collectlon efficiency was still 100% for SO, and NO,, but dropped to 80 % for COP The relative standard devlatlon for the three determlnatlons was as follows: SO,, 0.2-8%; NO,, 3 4 % ; and CO,, 2-8%. Further work Is needed to determine the error In the SO, determlnatlon caused by H,S04 absorptlon.
+
Environmental Protection Agency (EPA) regulations (1) require that electric utility plants monitor SOz and NO, emissions on a continuous (24 h) basis. COz continuous emission data are also needed so that emissions can be reported in the units of the EPA standard (pounds of pollutant/million Btu of heat input). These regulations also require that continuous monitoring be utilized to determine the efficiency of flue gas desulfurization (FGD) systems that are used to reduce SO2 emissions. This, of course, means monitoring upstream and downstream from the control system. We report here on a manual 24-h integrated sampling method in which all three pollutants are collected in one sample, by conversion to their ions, and then analyzed by ion chromatography. Thus, the method is cost effective in that all three pollutants are quantified with one monitoring system. In addition to being used as a separate routine monitoring method, the method could be used in place of SO2 and NO, instrumental methods, when they are inoperative. Work on development of this method for use upstream and downstream from FGD systems, with field testing downstream from a FGD system, is the subject of this paper. EXPERIMENTAL SECTION Laboratory Samplings. Simulated emission atmospheres were generated by flow dilution of SO2,NO, and COPatmospheres contained in cylinders the contents of which had been analyzed;
water vapor was added by bubbling the dilution g:.s (02in N,) through water. Samples were collected in 0.25 M KMn04-1.25 M NaOH solution contained in three restricted-orificeimpingers using the sampling system shown in Figure 1. Because of the high concentration of COz in source emissions, it was desirable to maximize the OH- concentration in the absorbing solution. Therefore, NaOH, KOH, and LiOH were tested for solubility in 0.25 M KMn04 solution at 10 "C. NaOH had the highest solubility, but increasing the concentration from 1.25 to 1.50 M precipitated KMnO,. Therefore, 1.25 M NaOH was used in all samplings. Field Testing. Field testing was conducted at a coal-fired electric utility plant with a generating capacity of 917 MW; the coal being burned contained 4.2% (w/w) S. Sampling was conducted downstream from particulate and SO2 emission control systems. SOz emissions were controlled by a wet injection process based on MgO and CaO. The stack gas temperature was 126 OF; the gas was saturated with water and contained water droplets. Reference Measurements. Data obtained from continuous emission monitors (CEMS) were intended for use as the standard for determining the SOz,NO,., and COz collection efficiency (CE) of the alkaline permanganate (A-P) sampling systems. However, the SOz CEM exhibited a negative bias presumably due to the high moisture content of the emissions. This bias was observed in spite of the sample conditioning system (see below). Therefore, EPA Method 6 (ref 1,appendix A, pp 455-460) was used as the reference measurement for the SOz determinations. During each 24-h run, 20-min samples were taken at discrete hourly intervals. The SO2concentration for each 24-h run was the arithmetic mean of the 24 EPA Method 6 results. NO,, COz, and Oz concentrations were determined with a transportable continuous emission monitoring system which was designed, operated, and calibrated according to a published protocol (2). Samples were extracted from the stack using a 180 cm long, 10 mm i.d. heated borosilicate-glass probe. A polyethylene bottle was fitted at the probe inlet in order to remove water droplets and thereby minimize demands on the sample conditioning system. (The same system was used with the probe for taking Method 6 samples.) A plug of cleaned (2-propanol/ water) borosilicate-glass wool was placed within the probe and near its inlet to remove particulate matter. The temperature of the gas stream at the plug was monitored with a thermocouple and maintained at approximately 302 OF. The probe outlet was connected to a conditioning system which consisted of a condenser, designed to lower the water dew point of the sample stream to 0 "C, and a 120 cm long Perma Pure dryer which operated to further lower the dew point. The outlet of the conditioning system was connected to a manifold which served three analyzers. NO,, COz, and Oz concentrations were determined with a Beckman Model 951 (chemiluminescence),a Beckman Model 864 (NDIR),
0003-2700/85/0357-1586$01.50/00 1985 American Chemical Society
