Improvements in the Collection of Hydrogen Sulfide in Cadmium Hydroxide Suspension W. L. Bamesberger and D. F. Adams Air Pollution Research Section, College of Engineering Research Division, Washington State University, Pullman, Wash. 99163
The technique of collecting hydrogen sulfide at ambient air concentrations in cadmium hydroxide suspension, in use for more than I O years, is reported to prevent loss from sulfide oxidation, A comparison of this procedure with bromine microcoulometric titration and with calculations of the anticipated hydrogen sulfide concentrations produced in a laboratory gas dilution system revealed an unpredictable and nonreproducible loss of hydrogen sulfide as high as SO% during collection of a 2-hour impinger sample containing cadmium hydroxide suspension. This paper provides evidence of the photodecomposition of cadmium sulfide in the impinger and describes techniques to reduce loss of sulfide during sampling and storage. The suggested modification provides reproducible hydrogen sulfide recoveries. Reliable quantitative results were obtained
B
ecause sulfide is known to oxidize rapidly in dilute alkaline solution, many absorption solutions involving the precipitation of sulfide with heavy metal ions have been tried in an attempt to minimize this oxidation and yet permit the subsequent colorimetric determination of the collected sulfide (Mecklenburg and Rosenkrauzer, 1914). A review has been published by Jacobs, Braverman. et rrl. (1957). The Jacobs method (alkaline cadmium hydroxide-methylene blue) was used in this laboratory in an attempt to establish the hydrogen sulfide concentrations in each stage of a twostage, dynamic gas dilution system associated with a series of odor threshold chambers (Sullivan. Adams, et d., 1968). The first-stage hydrogen sulfide concentration was continuously monitored with a Barton, Model 286, electrolytic titrator. These analyses were compared against the chamber concentrations as calculated by using the measured dilution ratios in the two-stage dilution system and independent analyses of the final dilutions made with a sensitive bromine coulometric microtitration cell (Adams, Jensen, et a / . , 1966). The final dilution concentrations as obtained by calculation and microcoulometric titration agreed within *lo%, whereas the wet chemical method gave concentrations approximately 10% of the other values for the final dilution. Mueller (1966) encountered similar unexplained losses of sulfide at low concentrations in his laboratory using the cadmium hydroxide absorption mixture. The possibility that the observed loss could be related to low collection efficiency had been eliminated by the work of Bostrom (1966), wherein the collection efficiency for isotopic H?S* in cadmium hydroxide suspension was found to be in the range of 93 to 98%;;.The CdS* collected in the absorption solution was oxidized to S*04'- with hydrogen peroxide in slightly acid solution. Unfortunately, the analytical method 258
Environmental Science & Technologj
did not provide any information concerning the fate of the S*2- during aspiration and storage, since analyses were based upon the amount of BaS*OI precipitated from the S*O4'- produced by the complete oxidation of CdS*. Marbach and Doty (1956) experienced the lowest sulfide losses either when the cadmium was completely precipitated with an equimolar addition of NaOH (pH 9.6) or when an excess of NaOH was present (pH 13.0). Marbach and Doty used the equivalent of 4.3 grams of 3 C d S 0 4 . 8 H ? 0and 1.3 grams of NaOH to prepare their fully precipitated Cd(OH)? sulfide collection media. Subsequently, Jacobs, Braverman, et ul. (1957) recommended only 0.3 gram of NaOH per liter (pH 7.5). Jacobs, Braverman, et a / . emphasized the problem of the oxidation of sulfides by the relatively large volumes of air which were aspirated through an impinger and suggested that oxidation was minimized by using the alkaline cadmium hydroxide absorbing mixture. This paper describes a study of the possible causes of the observed low recovery of concentrations of hydrogen sulfide from our gas dilution system as determined by the Jacobs method, which were believed to be related to changes in the sulfide following collection in alkaline cadmium hydroxide. E.~periiiientul Reference Hydrogen Sulfide Atmospheres. Permeation tubes (O'Keeffe and Ortman, 1966) were used for preparing accurate "primary" standard low concentrations of gaseous pollutants. The tubes were weighed periodically to establish the standard rate of H.S loss. They were thermostated to +O.l "C. and the air flow over the tube was measured accurately for calibration purposes. Reagents, HYDROGEN SULFIDESTOCKSOLUTION, 1 ml. = 0.44 ,pg, of sulfide. Three hundred milliliters of hydrogen sulfide gas were injected into 1 liter of freshly boiled, deaerated, 0.1N sodium hydroxide solution in a volumetric flask previously flushed with nitrogen. The flask was stoppered immediately with a serum cap and measured volumes of standard were withdrawn with a 10-ml. hypodermic syringe, the void being replaced immediately with an equal volume of nitrogen. The solution was standardized with standard iodine and thiosulfate solutions in a nitrogen atmosphere to minimize air oxidation. HYDROGEN SULFIDE TESTSOLUTION, 1 ml. = 4 pg. of sulfide. Ten milliliters of stock solution were diluted to 1 liter, using the deaeration procedure used to prepare the stock solution. A standard solution of S2- for less precise work was prepared by heating 100 ml. of 0.1N NaOH in an Erlenmeyer flask to drive out dissolved gases, purging the air space with N:. and immediately stoppering the flask. The 0.1N NaOH was then chilled t o 4" C. Just prior to use, 1 ml. of pure H,S gas was injected slowly into the 0.1N NaOH, and the flask
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was stoppered and shaken vigorously to absorb all the HYS into the solution. Samples may be transferred with a n ordinary pipet. The solution is stable for only about 30 minutes at room temperature. The calculated concentrations of the solution prepared above is approximately 13.0 pg. of H2S per ml., depending on temperature and barometric pressure. Seven solutions prepared in this manner gave a mean concentration of 12.3 pg. of H2S per ml. and a standard deviation of 1 0 . 3 pg. of H S per ml. CADMIUM HYDROXIDE ABSORPTIONSUSPENSION. Four and three tenths grams of cadmium sulfate, 3 C d S 0 4 . 8 H z 0 ,were dissolved in water, and 0.3 gram of sodium hydroxide was added and diluted to 1 liter. The suspension was mixed well each time before using. AMINE-ACID STOCKSOLUTION.Fifty milliliters of concentrated sulfuric acid were added to 30 ml. of distilled water and cooled. Twelve grams of N,N-dimethyl-p-phenylenediamine were added and stirred until dissolved. AMINE-SULFURIC ACIDTESTSOLUTION.Twenty-five milliliters of stock solution were diluted to 1 liter with 1 to 1 sulfuric acid. FERRIC CHLORIDE SOLUTION. One hundred grams of ferric chloride octahydrate were dissolved in water and diluted to 100 ml. The standard sulfide and amine solutions were refrigerated when not in use. Color Development. Three milliliters of amine test solution and 1 drop of ferric chloride solution were added to each absorption mixture and agitated after each addition. The mixture was transferred t o a 50-ml. volumetric flask, made up t o volume with distilled water, and allowed to stand for 30 minutes. A reference was prepared in the same manner by adding the amine and ferric chloride reagents t o an equal volume of unaspirated alkaline cadmium hydroxide suspension and was used in setting the colorimeter zero. The absorbance of the samples was read at 670 mp and the hydrogen sulfide concentration determined from a previously prepared standard curve. Procedure. All experiments were conducted with midget impingers containing 10 ml. of well-mixed cadmium hydroxide suspension. Aqueous standards were prepared by introducing measured volumes of dilute aqueous hydrogen sulfide beneath the surface of the absorption solutions with a hypodermic syringe o r pipet. Reference atmospheres were produced with permeation tubes. Four major treatments were used to study the losses of hydrogen sulfide: immediate development of the methylene blue color following addition of hydrogen sulfide to the absorption solution; development of the color following varying storage periods from 1 to 24 hours after the hydrogen sulfide was added to the absorption mixture in stoppered flasks with no aspiration but in contact with air, nitrogen, o r oxygen at the liquid-air interface; storage in light and dark, at various temperatures, and with various added protective agents ; and development of color following aspiration for 2 hours at an air flow of 2 liters per minute (with and without storage delays up t o 24 hours).
Table I. Loss of S2- on Standing in Cd(OH), Suspension Standing in Gas Phase, Loss Standing. Hr. Light, Hr. Nz Air 0 2
4 8 16 20 24
30 62 15 36 37
4 8 1 5 9
41 73 20 44 60
38 71 8 41 57
ene blue method. The sulfide loss for each purge treatment for each time interval is shown in Table I. Sulfide losses were not significantly greater for the air o r oxygen treatments than for the nitrogen treatment. The observed sulfide losses were, therefore, not directly related t o the presence of oxygen. Effect of Light. While studying the oxygen effect the sulfide loss appeared to be related to the length of exposure t o laboratory light. The data indicated a possible photodecomposition of the sulfide. Known concentrations of sulfide were added t o 15-ml. aliquots of cadmium hydroxide suspension, half of which STRactan 10 (arabinogalactan) additive. contained 1 Replicated samples were then stored for various intervals between l and 24 hours under laboratory fluorescent lights (approximately 60 foot-candles) and in the dark. The exposed and unexposed samples, with and without STRactan 10, were immediately analyzed by the methylene blue method following each storage period to determine the sulfide recovery (Figure 1). Cadmium sulfide exposed t o light in the absence of STRactan 10 showed an exponential sulfide loss with time. Significant improvement in sulfide recovery was obtained from cadmium sulfide in the presence of 1 STRactan 10 either in the light or dark. The linear sulfide loss appeared to be directly related to storage time. From these results it is apparent that photodecomposition of sulfide is a major cause of low recovery of sulfide from alkaline cadmium hydroxide suspension during storage. Effect of pH. Since the Jacobs (Jacobs, Braverman, et al., 1957) cadmium hydroxide suspension had a p H of 7.5 and the best Marbach and Doty (1956) suspensions ranged in p H from 9.6 to 13.0, the alkaline p H range was re-examined t o determine the importance of p H in the recovery of sulfide following aspiration and standing. Four cadmium hydroxide suspensions were prepared with p H of 7.5.9.0, 10.5, and 12.0. Ten milliliters of each suspension
80
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Effect of Oxygen. Replicated impingers containing 10 ml. of Cd(OH)? suspension were purged with nitrogen, air: and oxygen, respectively. A known concentration of S2- was added to all the samples and they were stored for various intervals from 4 to 24 hours and then analyzed by the methyl-
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STORAGE
Figure 1.
12 TIME
14
16
18
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Effect of light on CdS in Cd(OH).: suspension Volume 3, Number 3, March 1969 259
were placed in four sets of impingers. STRactan 10 was added to two sets of impingers (1 final concentration) and a known concentration of sulfide added to each impinger. All impingers were immediately placed in a dark room. One set of samples was stored and the comparable samples were aspirated for 2 hours at 2.0 liters per minute. Sulfide was then determined by the methylene blue method. The results are plotted in Figure 2 as per cent recovery against pH. Samples containing STRactan and those of higher p H gave consistently higher sulfide recoveries ; however, the improvement in per cent sulfide recovery is minor. Antioxidants. Atkin (1950) partially stabilized sulfite solutions by the addition of glycerol. Bender and Jacobs (1962) stabilized lead sulfide standards by adding gum acacia. In both procedures phenolic o r alcoholic groups were correlated with the reported stabilization of these sulfur compounds in their original oxidation state. A series of similar compounds and commercially available antioxidants was screened to establish their sulfide-stabilizing effectiveness and their influence upon the subsequent analysis of sulfide by the methylene blue colorimetric method. Antioxidant-alkaline cadmium hydroxide collecting mixtures were prepared by adding the appropriate weights of antioxidant to alkaline cadmium hydroxide collection mixture. Ten milliliters of the antioxidant-alkaline cadmium hydroxide collection suspension were placed in the midget impingers, standard hydrogen sulfide was placed beneath the surface of the collecting liquid by syringes, and the mixtures were aspirated for 2 hours, and analyzed by the methylene blue method. Comparable unaspirated samples were immediately analyzed. Table I1 lists the compounds studied, their stabilizing effect, and their influence upon the subsequent methylene blue analysis. STRactan 10 showed the greatest protective capacity of the compounds evaluated. Effects of Aspiration. Losses occurring during aspiration were further examined by aspiration of dynamic gaseous dilutions of H?S produced from permeation tubes. Using this technique, gaseous dilutions were made in nitrogen, oxygen, and air (Table 111). Comparable recoveries of HrS from nitrogen, oxygen, and air indicate that a possible oxygen reaction with the sulfide is not significantly related to the low sulfide recovery experienced. The HnSrecovery was primarily dependent upon the amount of light exposure (Figure 1) and addition of 1 STRactan 10 to the absorbing solution effectively protected the collected sulfide from photodecomposition.
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suspension in the dark 260
En,ironmental Science & Technolog)
None Di-tert-but yl-p-cresol G u m tragacanth Glycerol
2,5-Dihydroxy-l,4-benzoquinone G u m acacia Dithiothreitol Dithoerythritol STRactan 10 (arabinogalactan)" Tannic acid /-Ascorbic acid
2,4,5-Trihydroxybutyrophenone
0.1 0.2 1 .o 0.1 0.5 0.02 0.02 1. 0 1.o 2.0 0.1
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0 Registered trade-mark, St. Regis; Stein-Hall and Co., Inc., distributors. Interfered with development of methylene blue color. (2
Table 111. Oxidation cs. Photodecomposition of Hydrogen Sulfide Collected in Jacobs Cd(OH)2 Suspension Dilution Light H2S Gas Hr. F g . H?S/Sample Recovered,b
Ne 0 2
Air
0 0 0 2 24
81.8 80.0 79.4 62.2 2.9
11.78 11.52 11.43 8.96 0.42
a Fluorescent light of 60-ft.-candle intensity. Exposure time includes sampling time. h Samples taken at 2.0 litsrs'min., for 120 min. f r o m permeation tube \\ith loss rate of 0.120 pg. HzS,'min. Thus H?S is diluted to 79 p.p.b. and 100 recovery would represent 14.40 f i g . H?S/sample.
The addition of STRactan 10 to the absorbing solution produced some foaming during aspiration, resulting in a small carryover of absorbing solution from the impinger. The addition of 5 ml. of 95 ethanol to the impinger prior to aspiration prevented this loss without affecting collection efficiexy, storage stability of collected samples, or interference with the analytical procedure. Subsequently, Levaggi (1968) suggested using a mechanical demister consisting of a perforated Teflon disk slipped up over the impinger air inlet to prevent absorbant carryover. Reproducibility. Eighteen samples were collected from permeation tubes at two different concentrations and with different amounts of light exposure and storage time to test the reproducibility of the method with 1 STRactan and 5 ml. of ethanol added to the impinger. An average of 79.9% of the H2Swas recovered with a standard deviation of *3.5 %. Since the recovery of H2S is now reproducible at 79.9%;, raw data can be corrected to 100% recovery by multiplying by 1.25, o r dividing by 0.799.
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Table 11. Effectiveness of Antioxidants for Protection of S2- as CdS in Cd(OH)? Suspension Added S 2 - Loss
All reagents are prepared as described under Experimental, except the cadmium hydroxide absorption suspension. CADMIUMHYDROXIDE-STRACTAN ABSORPTIONSUSPENSION. A 4.3-gram sample of cadmium sulfate, 3CdSO1.8H20, and 10 grams of STRactan 10 were dissolved in distilled water. Sodium hydroxide (0.3 gram) was dissolved in distilled water, diluted to 1 liter, and mixed well before using. Midget impingers were filled with 10 ml. of cadmium hydroxide-STRactan suspension, Foaming was suppressed by adding 5 ml. of 95 ethanol or placing a Teflon disk around
the air inlet tube about 1 inch below the top of the impinger. Each sample was aspirated at 2.0 liters per minute for not more than 2 hours each. The collected samples were stored at room temperature and protected from bright light. Samples should contain between 1 and 20 pg. of hydrogen sulfide and should be analyzed as soon as possible after collection. Distilled water was added to each sample to replace evaporative losses. Three milliliters of amine test solution and 1 drop of ferric chloride solution were added to each impinger and agitated vigorously immediately after each addition. The sample was transferred to 50-ml. volumetric flasks, made up to volume with distilled water, mixed, and allowed to stand for 30 minutes. A reference was prepared in the same manner by adding the amine and ferric chloride reagents to 10 ml. of unaspirated alkaline cadmium hydroxide suspension. The colorimeter was zeroed against the reference. The absorbance of the samples was read a t 670 mp, The hydrogen sulfide concentration was calculated from a standard curve and the volume of air sampled.
of H2S by volume in air. Under these conditions consistent H2S recoveries in the order of 80% can be achieved, and the results can be mathematically corrected to 100%. The sensitivity of this method is substantially below the human olfactory response and the usefulness of the method for ambient air analysis has been greatly enhanced. Literature Cited
Conclusion Sulfide losses can be minimized by adding 1 % STRactan 10 to the absorption mixture, avoiding exposure to light, and analyzing samples as soon after collection as possible. Assuming a 2-hour sample taken at 2.0 liters per minute and an analytical sensitivity of 1 Fg. of HnS per 50-ml. sample, the over-all sensitivity of the method is a few tenths of 1 p.p.b.
Adams, D . F., Jensen, G. A., Steadman, J. P., Koppe, R. K., Robertson, T. J., Anal. Chem. 38, 1094 (1966). Atkin, S., Anal. Chem. 22, 947 (1950). Bender, D. F., Jacobs, M. B., Analyst 87, 759 (1962). Bostrom, C . E., Air Water Pollution Intern. J . 10, 435 (1966). Jacobs, M . B., Braverman, M. M., Hochheiser, S., Anal. Chem. 29, 1349 (1957). Levaggi, D. A., personal communication, 1968. Marbach, E. P., Doty, D. M., J. AGR. FOODCHEW4, 881 (1 956). Z . Anorg. Cliem. 86, 143 Mecklenburg, W., Rosenkrauzer, F., (1 9 14). Mueller, P. K., private communication, 1966. O'Keeffe, A. E., Ortman, G. C., Anal. Chenz. 38, 760 (1966). Sullivan, D. C., Adams, D. F., Young, F.A., Atmos. Enciron. 2, 121 (1968). Receicedfor reciew June 21, 1968. Accepted December 5, 1968. Research supported in part by a grant from the Paci3c Northwest Pulp and Paper Association and Grant No. AP-00215, Dicision of' Air Pollution, U S .Public Health Sercice. Dicision of Water, Air, and Waste Cliemistrj., 155th meeting, A C S , Sun Francisco, Calif., April 1968.
Contribution of Aerial Contamination to the Accumulation of Dieldrin by Mature Corn Plants Harold L. Barrows, Joseph H. Caro, and Walter H. Armiger U S . Soils Laboratory, Soil and Water Conservation Research Division, Agricultural Research Service, U S . Department of Agriculture, Beltsville, Md. 20705
William M. Edwards North Appalachian Experimental Watershed, Soil and Water Conservation Research Division, Agricultural Research Service, U S . Department of Agriculture, Coshocton, Ohio 43812
Greenhouse and field experiments were conducted in which corn was grown on Muskingum silt loam containing added amounts of dieldrin. The plants grown in the greenhouse were protected from aerial contamination, whereas no attempt was made to control this in the field. The corn was harvested at maturity, and the dieldrin contents of the leaves, stalks, kernels, and cobs were determined. Only slight differences were found between the two experiments in the
A
mple evidence exists that plants d o accumulate dieldrin and other organochlorine insecticides (Duggan and Weatherwax, 1967; Lichtenstein et a/., 1965; Lichtenstein and Schulz, 1960; Saha and McDonald, 1967). It has generally been presumed that this resulted from root uptake and translocation. Controlled experiments have demonstrated that these compounds are taken up by the plant roots (Lichtenstein and Schulz, 1960; Nash, 1968; Wheeler et al., 1967), and that
dieldrin contents of the stalks, kernels, and cobs. The leaves of the field-grown plants contained much higher concentrations than those grown in the greenhouse. The leaf-tostalk ratio of dieldrin concentrations in the field-grown plants was 50 times higher than that found in the protected plants. This large difference is attributed to aerial contamination of the foliage.
they are translocated throughout the plants. Pressure is mounting to devise a method for predicting plant uptake from a given soil. Work to date has generally followed the established pattern of correlating concentrations in whole plants or selected plant parts with soil concentrations and various soil factors. Some of this work has shown promise (Bruce and Decker, 1966; Lichtenstein et a/., 1965; Nash, 1968). However, all of this work was based upon the premise Volume 3, Number 3, March 1969 261
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