4) Corsini, A., Graham, R. P., Anal. Chim. Acta 28, 583 (1963). (5) Derbyshire, D. H., Waters, W. A., J . Chem. SOC.1950, 564. (6) Devanathan, RI. A. V., Fernando, Q., Trans. Faraday SOC.52, 1332 (1956). (7) Fernando, Q., Devanathan, RI. A. V., Rasaiah. J. C.. Caloin. J. A.. Nakulesparan, K.,J . ‘Eleckoanal. Chem. 3, 46 (1962). (8) Griffith, R. O., McKloxn, M., Winn, A. G., Trans. Faraday SOC. 28, 101 (1932). (9) Hollingshead, R. G. W., “Oxine and
Its Derivatives,” Vol. I, p. 40, Butterworths, London, 1954. (10) Kolthoff, I. R l . , Tanaka, N., ANAL. CHEM.26, 632 (1964). (11) Kozak, G. S., Fernando, Q., Anal. Chznz. Acta 26, 541 (1962). (12) Kozak, G. S., Fernando, Q., J . Phys. Chem. 67. 811 (1963). (13) Laitinen, H. A.; Kolthoff, I. RI., Ibid., 45. 1074 (1941). (14) Liebhafsky, H. A.’,J . A m . Chem. SOC. 5 6 , 1500 (1934). (15) PhilliDs. J. P.. Emerv. J. F.. Price.’ ‘ H. P., LNAL. CHEW 24,“io33 (1952).
(16) “Reagent Chemicals,” p. 180, Am. Chem. Soc. Specifications, Am. Chem. Soc., Washington, D. C., 1950. (17) Robertson, P. W., Mare, P. B. D. de la, Swedlund, B. E., J . Chem. SOC. 1953, 782. (18) Scaife~D. Tyrrel*, H. J. v., Ibrd., 1958,386. RECEIVEDfor review August 15, 1963. Accepted October 3, 1963. Presented in part before the International Union of Pure and Applied Chemistry, London, 1963. Work supported by the National Institutes of Health. B.j
Rapid Volumetric Determination of Sulfide in Estuarine and Sea Waters CLYDE R. JOHNSON, PAUL H. McCLELLAND, and ROBERT L. BOSTER Portland State College Public Health laboratory, Portland, Ore. In about 100 analyses of polluted waters, ASTM Designation D 1339-54 T was found suitable for use unchanged to determine sulfite. With the same samples, the standard evolution method for determination of sulfide gave incomplete recoveries. A new method based on separation of zinc sulfide b y inverse filtration and titration in inert atmospheres was tried. It was capable of recovering 0.2 mg. of sulfide from liter samples of sea water accurately to within 0.01 mg., that is, to better than 1 part in 100 million. The inverse filtration method may be used to determine sulfide in the range 0.2 to 53 mg. per liter with a relative standard deviation averaging about 1.470. Analysis of an equilibrated sample requiresonly 15 to 30 minutes. Although designed for use with estuarine and sea waters, the method is suitable for determination of sulfide in water, waste water, and possibly sewage.
I
N
A
STUDY O F
POLLUTED
WATERS
from Coos Bay, about 100 samples containing sulfite in the range 0.03 to 9.5 mg. per liter and sulfide up to 440 mg. per liter were analyzed by ASTRI Designation: D 1339-54 T, the tentative method of test for sulfite ion in industrial water (4). It was found that this method could be used unchanged, provided the sulfide present was fixed as zinc sulfide. For some of the same samples, attempts were made to apply the method for determination of sulfide by evolution as hydrogen sulfide in a current of C 0 2or NzJ collection again as zinc sulfide, and determination with iodine-thiosulfate standards ( 2 ) . Re-
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ANALYTICAL CHEMISTRY
covery of sulfide was alwayi: incomplete, even when the gas trains were operated for six hours a t rates from 35 to 80 ml. per minute. The APH;I procedure as designed for water, sewage, and industrial wastes ( 2 ) implies that recovery may require more than an hour, but is indefinite regarding time required for complete recovery. Budd and Beivick (5) describe the recovery of sulfide by their variation of this method as incomplete but reproducible. They also state as a generalization that sulfide Polutions are very unstable. Dilute sulfide standards used in the present work decomposed quite rapidly, apparently with release of sulfur, even when kept under inert gases. Since there is no reason whv sulfide solutions should cease to be unstable while in the sample flask of the evolution method, it might be concluded that the incomplete recovery is due to decomposition. However, there are some reports of excellent recoveries by the method (1, 6) sometimes side by side with records of incomplete recovery. Stability of sulfide in sealed samples containing excess zinc acetate is generally accepted (1, 2 ) .
On the possibility that difficulties with the method might be due t o the complex nature of polluted sea m-ater, an attempt was made to solve the problem of removing potential interferences in a reasonable time by separating the sulfide, fixed as zinc sulfide and kept in inert atmospheres, by some techniques centered around inverse suction filtration and siphoning. Preliminary experiments were promising; the procedure was therefore studied in detail with synthetic samples, at six concentrations over the range from 0.20 to 53 mg. of
sulfide per liter. For comparison purposes parallel analyses of similar samples mere made by the evolution method ( 2 ) . EXPERIMENTAL
Two variations of the apparatus used in the new procedure are shown in Figure 1, together with the siphon tube which is the basis of the simpler version. This tube is a coarsc-porosity gas diffusion tube 10 mm. in diameter with a 25-mm. frit, as used in thc siphoning apparatus a t the upper left in the figure. Separation by siphoning is preferred; however, if the zinc sulfide must be washed before dissolving it, samples are taken in quart fruit jars t o permit use of a separatory funnel for washing in an inert atmosphere. In this case, separation and washing are effected under gentle suction in the other apparatus shown, which has a 30-mm. diameter medium-porosity frit a t the end of an 8-mm. diameter tube. Both fritted filters are stock items. The 2.4-liter bottles are gas reservoirs, by which inert atmospheres are maintained during the separation and subsequent titration, which is carried out in the original sample container, without transfer. One of the t\vo gas trains used in the evolution method is shown in Figure 2. In this train, tank CO, was washed with alkaline pyrogallol ( 3 ) . In a similar train, reagent grade tank K2 was passed through a Sargent S-36517 furnace containing an S-36518 Vycor tube with copper turnings a t 450” C. Reagents. Standard 0.025 and 0 . 1 s iodine and thiosulfate solutions were prepared by the usual methods (2) and stored in the dark. These, with 5- and 50-ml. calibrated burets, covered the range required. Sulfuric Apparatus and Reagents.
Figure 2. Figure 1.
Evolution method apparatus
Inverse filtration met Id apparatus
acid, 3GN, was distilled in a retort am stored in horosilicate glass, after rejec tion of head and tail fractions. Stand ard sulfide solutions were made b: dilution of stock 5N sodium sulfidi synthesized and stored in polyethylene in the dark. These stock solution. were prepared by weight titrations fron pure hydrogen sulfide and reagent gradi sodium hvdroxide. Comnarison of thi weight titration data wiih analyses o the stock solutions and the freshlj prepared and quickly used standard proved that substantially all of thi sulfur in the latter was in the sulfidi form. Dilutions were made under CO or N2, some with sea water, some wit1 boiled and cooled demineralized water For such dilutions, and for the syn thctie samples, standards, and blanks four unfiltered 5-gallon quantities o water were taken on different days 01 the incoming tide, in the channel be tween Coos Bay and the Pacific Ocean These arc referred to herein as se: water, and although not strictly rep resentative of open-ocean samples thei salinity was between 30 and 33°/or This sea water was always boiled befor, use, then cooled in a polyethylene siphoiU bottle under COa or N2. With se;9. water dilution, the heavy white pre cipitate which formed was settled ani1 filtered off, pFoducing surprisingly little discrepancy in the above comparisonrl. Water was prepared from very soft Portland water by passage through tw,D Deeminizers. It always had a conductivity equivalent to about 0.2 p.p.m of sodium chloride, hut in the 100- ts0 250-ml. quantities used in analyseS showed reducing impurities equivalent to a few tenths of a milliliter of 0.025)r iodine. The normalities of the iodin e and thiosulfate changed st rates measur able in days, the diluted sulfide stand ards a t ra'ces noticeable in half-hou r intervals; corrections were applie,d accordingly.. Water and sulfide solu!tions were kept in polyet,hylene, iodim!, and thiosulfate in borosilicate glass. Synthesis Pattern. For the in verse filtration method study, siX sets of synthetic sea water sampler :, a t least eight in each set, were pre pared and analyzed. Prior to eac!h set of syntheses the iodine, thiosulfate!,
and sulfide standards of appropriate concentration were restandardized against potassium dichromate and occasionally .checked against potassium iodate, primary standards. To make each synthetic sample, a clean 32-ounce bottle or quart jar was filled with inert gas. Two milliliters of 2N zinc acetate (equivalent to 64 mg. of S-3 were added, followed by a standard sulfide solution aliquot. The sample container was then filled with sea water from a siphon bottle, and promptly sealed. Three other similar samples were quickly made, and two blanks from which sulfide was omitted. Just before and sometimes also just after the syntheses, four to six aliquots of the diluted sulfide standard equal in size to those used in the syntheses were analyzed by the procedure described below. The analysis of these aliquots showed regular decreases in the sulfide Concentration which made it necessary to keep records of synthesis and analysis times, and to determine the amount of sulfide added by interpolation or extrapolation. The samples were allowed to stand from 4 to 11 days before analysis. Synthetic samples for the evolution method study were prepared by introduction of aliquots of the sulfide standards into 500-ml. portions of boiled, cooled sea water which had been placed in the 3-necked flasks of the gas trains and treated for 30 to GO minutes with streams of GOz or Nz. This, in effect doubled the concentration range over that of t.he other study. Procedure. The following analytical procedure is described mainly in terms of t h e preferred siphoning version of the inverse filtration method. Suitable variations were applied to all of the synthetic samples, and the procedure may also be used for collected samples. Unknown samples to which the customary (2) 2 ml. of 2N zinc acetate per liter have been added should be checked for hydrogen sulfide odor, and additional amounts of zinc acetate added and the sample allowed t.0 stand until precipitation of zinc sulfide is complete and no odor of hydrogen sulfide is detechhle. To start a typical analysis a siphon
filter attached as shown in Figure 1 to an inert gas reservoir was lowered into the sample bottle and suction was applied to prevent overflow and to start the siphon. The seal was completed quickly and the siphon adjusted so the frit barely touched the bottle and the flow was in fast drops. The first portion of the siphonate was rejected, the next collected in a COSfilled, graduated beaker from which a 100- to 200-ml. sample was transferred to a COS-filled bottle and promptly analyzed for sulfite (4). Alternatively, these operations were carried out using suction filtration in the lower apparatus shown in Figure 1. Subsequent results showed that this variation was seldom required. Meanwhile, as the siphoning proceeded, 100 ml. of water, 1 ml. of 3GN sulfuric acid, and 1 ml. of 1% starch solution were added to a beaker filled with C02. In lieu of a blank, this solution was balanced t o the faint blue end point with the iodine-thiosulfate combination. When siphoning was complete, the sample bottle was tipped and the liquid blown from the tube. The rubber tiibes were removed, the bottle was opened, and the balanced solution was poured down the siphon tube to rinse it into the bottle; the tube was removed to a clean rack. The titration was continued in the bottle in the inert atmosphere, the bottle being closed and shaken with excess iodine present to pick up any hydrogen sulfide in the vapor phase. Then, near the end point, with excess iodine, the siphon
verse Filtration Method Sulfide Rel. Sulfide found ' Std. dev., dev., std. added, mean mg.S-2/1. % mg./l. mg./l
!I
'9
.-
10.0022
VOL. 36. NO. 2, FEBRUARY 1964
I.!
"
301
Table 11.
Sulfide added, total nig. 0.34 1.70 6.36 7.99
21.4 23.8 47.4 0.088 i.5i 1.51 3.44 9.08 19.0 23.8 47.4
Recovery of Sulfide by Evolution Method
yo recovered Yo recovered yorecovered in 1 hour
in 3 hours
41 45 73 53 58 54 55 57 36 74 53 84 54
io
With COZ 75 83 79 71 81 85 66 83 90 92 71 68 73 74 With NI 82 85 81 90 77 83 80 83 89 90 75 80 75 76
to get any zinc sulfide adhering to the frit. The titration was completed by restoration of the initial blue color with thiosulfate. Analyses by this method required from 15 to 30 minutes each. I n analysis of samples for which the sulfide concentration was approximately known, a small excess of standard iodine was added just before the balanced acid-starch solution, t o release the hydrogen sulfide under iodine solution. RESULTS
Results of analyses of the synthetic samples by the inverse filtration method are given in Table I. Because of the instability of the sulfide standards, and because it was not practical t o prepare simultaneously four synthetic samples and two blanks, and to analyze four t o six aliquots of the sulfide standard, a simple comparison of replicate determinations of amounts added and amounts found cannot be made. Thus, the “sulfide added” column gives values extrapolated or interpolated to the midpoint of the time interval in which the corresponding synthetic samples were made. This treatment of the data introduces only a small uncertainty in the last figure reported in each case as the amount added, and the precision of the additions may be inferred from the precision of the amounts found. Each “sulfide found” is the average of four analyses, for which the standard deviation and relative standard deviation are given. The relative standard deviations include not only the errors inherent in the procedure, probably small, but also somewhat larger errors due to the s!ip of the sulfide standards and the slight exposure to air in pipetting the
302
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ANALYTICAL CHEMISTRY
in 6 hours
Residual, as mg. S-2
Gas flow, ml./min.
0.14 0.31 0.38 0.27 0.32 0.24 0.82
35 50 io 50 55 40 45
0.62 0.28 0.43 0.53 0.44 0.42 0.24
65-70 60-70 70-80 60-65 75-80 65-75 70-75
standards, during synthesis of the samples. I n the analysis of collected samples,where the latter two factors do not operate, the precision should be better, since a n inert atmosphere may be quite rigorously maintained. I n view of the absence of trends corresponding to the differing times which the synthetic samples stood before analysis, the results show clearly that once sulfide is fixed with excess zinc acetate, the change in the sulfide concentration stops completely for all practical purposes. That is, the method shows the sulfide concentration a t the time of sampling. It may be concluded also that the procedure measures the sulfide so fixed, with satisfactory speed, precision. and accuracy. The sensitivity is very good. At the 0.2-mg.-per-liter level, the easily reproducible 0.01-mg.per liter amount corresponds to 1 part in 100 million of sulfide in the sample, Results of the analyses of the synthetic samples by the evolution method (2) are given in Table 11. The “sulfide added” was obtained by extrapolation to the time of addition of the sulfide aliquot to the 3-necked flask, and the percentage amounts recovered are calculated on this as a basis, with less than warranted precision in view of the incomplete recoveries. The “residual” column shows the iodine demand of the samples remaining in the flask after the 6-hour runs, as milligrams of sulfide. Actually, it represents mainly the nonvolatile reducing impurities in the four unfiltered, nonuniformly aged sea waters. The gas-flow rates were measured either volumetrically or by soapbubble flowmeter and are given as approximate averages or ranges; it was not possible to maintain very constant flow rates during the long runs, inter-
rupted for the analyses of the combined absorption flask contents. The quantitative results fit the description given qualitatively by Budd and Bewick (5): recovery is incomplete but reproducible. The results are of course characteristic of the apparatus and conditions used. By control of conditions intentionally varied in the present study, results could be made more reproducible. Cnder such conditions, by use of a noristoichiometrical factor or by the device used by Rudd and Bewick, the method might be made to yield fairly consistent results. However, except for special purposes, there would seem to be little point in using the method when the inverse filtration method is applicable. The evolution method is essentially less accurate. less precise, less sensitive, more time consuming, and requires more elaborate equipment than the inverse filtration method. Also, when samples are to be analyzed for both sulfide and sulfite, with sampling precautions involving the latter, the evolution method brings up the frustrating problem of obtaining a representative sample from a heterogeneous system which also has a part of the material adsorbed on the container walls, under ronditions where exposure to air is fatal to accuracy. The inverse filtration method neatly avoids these difficulties. For the above reasons it is recommended that this method be studied further aq a possible supplement or replacement for the standard evolution method ( 2 ) in determinations of sulfide in mater, sewage, and industrial wastes. For such uses, the concentration range covered may be extended in either direction, for example by combination with the spectrophotometric methylene blue procedure. The method is now being used in a study of benthic faunal indicators of pollution in Coos Bay, a project directed by James A. Macnab of this laboratory. LITERATURE CITED
(1) Almy, L. H., J . Am. Chem. SOC.47,
1386 (1928); (2) Am. Public Health Assoc., Kew York, “Standard Methods for the Extrnination of Water and Wastewater. 11th ed., p. 330, 1960. f3) \ - , -Ihzd.. - - - I n. r 163. ---
(4) Am. S O ~ .Testing Mater., Philadelohia, Pa.. “ASTM Standards, 1955,” Pait 7,’p. 1477. ( 5 ) Budd. M. S..Bewick. H. -4.. ANAL. CHEM.24, 7536 (1952). (6) Ibid., p. 1540. RECEIVEDfor review August 20, 1963. Accepted November 12, 1063. This investigation was supported by Public Health Service Research Grant WP-0003643, from the Division of Water Supply and Pollution Control. ~
