216
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(8) Unger, K. K.; Becker, N. P. Presented at the 28th Pinsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, OH, 1977; Abstract No. 171. (9) Engelhardt, H.; Mathes, D. J . Chromatogr. 1977, 142, 311. (IO) Tomb, W. H.; Weetall, H. H. U.S. Patent 3783 101, 1974. (11) Stout, R. W.: DeStefano, J. J. J . Chrornatogr. 1985. 326, 63. (12) Japanese Patent 8005941, 1980. (13) Kirkland, J. J.; Yates, P. C. U.S. Patent 3722 181, 1973. (14) Kirkland. J. J.: Yates, P. C. US. Patent 3795313, 1974. (15) Jay, R. R. Anal. Chem. 1964, 3 6 , 687. (18) Fulcher, C.; Croweli, M. A,; Bayliss, R.: Holland, K. B.; Jezorek, J. R. Anal. Chirn. Acta 1981, 129, 29.
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RECEIVED for review March 9, 1987. Accepted September 18, 1987.
Determination of Trace Sulfides in Turbid Waters by Gas Dialysis/ Ion Chromatography Lorne R. Goodwin,* Donna Francom, Alessandro Urso, and Fred P. Dieken
Alberta Environmental Centre, Bag 4000, Vegreuille, Alberta, Canada TOB 4LO
The accuracy of the methylene blue colorhnetrlc procedure for the determlnatlon of sulflde In environmental waters and interferenceseven after wastewaters is Influenced by tuappllcatlon of recommended pretreatment technlques. The dlrect analysis of sutfkle by Ion chromatography (IC),wlthout sample pretreatment, Is compllcated by fleld preservatlon of samples wlth zinc Ion (or equlvalent). A contlnuous-flow procedure has been developed that converts the acld-extractable sulflde to H,S, whlch Is separated from the sample matrlx by a gas dlalysls membrane and then trapped In a dilute sodium hydroxlde solution. A 200-pL portlon of this solution Is Injected Into the Ion chromatograph for analysis wlth an electrochemical detector. Detectlon lhnlts as low as 1.9 ng/mL have been obtalned. Good agreement was found between the gas dlalysls/IC and methylene blue methods for nonturbld standards. The addltlon of ascorblc acld as an antloxldant is required to obtaln adequate recoveries from spiked tap and well waters.
Several analytical methods have been published for the determination of aqueous sulfides; however, the quantitation of nanogram-per-milliliter levels of sulfide in turbid and colored waters is subject to accuracy, precision, and sensitivity limitations. Most analytical procedures require time-consuming pretreatment techniques, including laborious preconcentration steps (e.g. gas displacement) to remove interferences prior to the quantitation step. The spectrophotometric methods outlined in ref 1, 2,5, and 6 are in general use (e.g. methylene blue standard method); however, the accepted pretreatment techniques for zinc-preserved environmental samples include alkalinity adjustment, settling, decanting, and resuspension on turbid samples, which result in high blank readings and interferences for low-level determinations of sulfide. The sulfide ion selective electrode method has been reported (3, 4) t o accurately measure sulfide concentrations at 10 ng/mL by using targeted calibration standards; however, the response is notably slow and interfering substances such as cyanide will produce a high bias for low-level determinations. Other analytical techniques such as gas chromatography (7), polarography and related electrochemical techniques (8,9),
atomic absorption spectrometry ( I I ) , thermometric titrimetry (12), and fluorometry (13) have been published. Unfortunately, each method is subject to interference or sensitivity limitations. The combination of an amperometric detection system with suggested ion chromatography separation techniques (14,15) a promising procedure for routine determination of sulfide in unpreserved environmental waters. Rocklin and Johnson (14)identified eluent compositions and strengths, column types, and electrochemical detection parameters for the simultaneous measurement of cyanide, sulfide, iodide, and bromide by ion chromatography. Bond et al. (15)also presented work demonstrating the determination of free sulfide and cyanide by ion chromatography while using several different electrochemical detector designs and eluents. Efforts to quantitate environmental water samples for nanogram-per-milliliter sulfide concentrations without zinc preservation have resulted in irreproducible peaks and unstable base lines. Rocklin (14)reported a detection limit of 30 ng/mL for sulfide and commented that extremely small quantities of sulfide (
