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due to large background currents or other sources will further shift the observed Ephhuand must also be taken into account. At higher applied potentials (typically >+1V), it may be necessary to select a potential less positive than Eplateau to minimize background current and noise. The pH dependence of the CV and HDV behavior of some of the phenols investigated indicated the presence of complicating chemical reactions, consistent with earlier observations (9). The consistency of the experimental results with the empirical relationship is therefore encouraging. When these precautions are heeded, the empirical relationship established here'is very useful in allowing rapid initial estimation from a single CV scan of the applied voltage required for detection of a compound of interest at an electrochemical LC or flow injection detector.
ACKNOWLEDGMENT The authors are grateful to Darryl Anderson of 3M Co. for supplying the Kel-F used in this work. LITERATURE CITED (1) Anderson, J. L.; Chesney, D. J. Anal. Chem. 1980, 52, 2156-2161. (2) Chesney, D.J.; Anderson, J. L.; Weisshaar, D. E.; Taliman, D. E. Anal. Chim. Acta 1981, 124, 321-331. (3) Anderson, J. E.; Taiiman, D. E.; Chesney, D. J.; Anderson, J. L. Anal. Chem. 9978, 50, 1051-1056. (4) Nicholson, 8.S.; Shain, I. Anal. Chem. 1964, 36,706-723.
(5) Blaedel, W. J.; Schieffer, G. S. J. Nectroanal. Chem. 1977, 80, 259-271. (6) Jordan, J; Javick, R. A. Nectrochim. Acta 1982, 6, 23-33. (7) Gaius, Z."Fundamentals of Electrochemical Analysis"; Haisted Press: New York, 1976; p 249. (8) Adams, R. N. "Electrochemistry at Solid Electrodes"; Marcel Dekker: New York, 1969; pp 363-369. (9) Vermilllon, F. J., Jr.; Pearl, I. A. J. Electrochem. Soc. 1964, f f f , 1392- 1400.
James L. Anderson* Department of Chemistry University of Georgia Athens, Georgia 30602
Duane E. Weisshaar Dennis E. Tallman* Department of Chemistry North Dakota State University Fargo, North Dakota 58105 RECEIVEDfor review August 22, 1980. Resubmitted January 22, 1981. Accepted February 9, 1981. This work was supported by the U S . Department of the Interior, Office of Water Research and Technology [Grants B-043 (J.L.A.), B-055 (D.E.T.), A-062 (D.E.T. and J.L.A.)], and the U S . Environmental Protection Agency [Grants R808084-01-0 (J.L.A.) and R803727-01-1 (D.E.T.)].
Measurement of Hydrogen Sulfide and Hydrogen Polysulfides in Sulfur Sir: Buyers of Claus process sulfur are showing increasing interest in the problem of monitoring hydrogen sulfide (present largely as hydrogen polysulfides) in sulfur. This is because of growing awareness of potential safety problems associated with the shipping and handling of this sulfur. The trace amounts of hydrogen polysulfides slowly weather off to give toxic (sometimes even explosive) amounts of hydrogen sulfide in the air space above the liquid sulfur in tank cars and trucks ( I ) . Because of this safety concern, we have done some work with analytical methods for measuring HZS and H2S, in liquid sulfur and would like to share our findings with the rest of the industry to aid in dealing with this safety problem. The main problem in doing a successful determination of all the free hydrogen sulfide and bound hydrogen sulfide (H2S,) is in assuring a complete breakdown of the hydrogen polysulfides during the course of the analysis. A method by Tuller (2) uses PbS as a catalyst to accelerate this breakdown while the H2Sis continuously removed from molten sulfur by a nitrogen sparge. The H2S is carried to zinc acetate absorption bottles where it is trapped as ZnS for later iodometric analysis. Tuller explicitly makes the point that a catalyst is required for the breakdown of hydrogen polysulfides. We would like to reemphasize the importance of using a catalyst. Failure to use a catalyst may give analytical results that are only a small fraction of those obtained when full degassing is achieved with a catalyst. Two small changes in the Tuller method were found to be helpful in our work. The Tuller method specifies a 2-h sparging period, but we found that somewhat higher values
could be obtained by using a 2.5-h degassing period. In addition, we found that the use of continuous magnetic stirring of the sulfur sample makes a significant difference in the degree to which the breakdown of hydrogen polysulfides may be taken to completion. For example, strict adherence to the Tuller method (using only occasional swirling of the sulfur) gave values of 296 and 265 ppm for the same sample, but addition of continuous power stirring gave 408 ppm for the same material. Although some concerns may arise that adding PbS to the sulfur might somehow cause an increase in the H2S content, we have been able to determine that this is not the case. We carried out the Tuller method of analysis (with added power stirring) on samples of sulfur that were completely degassed (by aging) before the analysis was begun. The results show no detectable H2S whether lead sulfide was added or not. We recommend that anyone wishing to monitor HZS and hydrogen polysulfides in sulfur either use this modified Tuller method or carefully check the method being used to make sure it correlates with this method. LITERATURE CITED (1) Donovan, J. R. Chem. Eng. Prog. 1982, 58, 92. (2) Tuller, W. N. "The Analytical Chemistry of Sulfur and Its Compounds"; Karchmer, J. H., Ed.; Wiiey-Interscience: New York, 1970.
T. H. Ledford Exxon Research & Development Laboratories Baton Rouge, Louisiana 70821 RECEIVED for review November 3,1980. Accepted January 19, 1981.
0003-2700/81/0353-0908$01.25/00 1981 American Chemical Society
