Standard Methods: 4500-S2- G: Sulfide by Ion-Selective Electrode
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Official Method Name
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4500-S2- G. Ion-Selective Electrode Method |
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Current Revision
| Standard Methods Online |
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Media
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WATER |
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Instrumentation
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Ion Selective Electrode |
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Method Subcategory
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Inorganic |
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Method Source
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Citation
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Brief Method Summary
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The potential of a silver/sulfide ion-selective electrode (ISE) is related to the sulfide ion activity. An alkaline antioxidant reagent (AAR) is added to samples and standards to inhibit oxidation of sulfide by oxygen and to provide a constant ionic strength and pH. Use of the AAR allows calibration in terms of total dissolved sulfide concentration. |
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Scope and Application
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The method can be used for a variety of waters and wastewaters. |
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Applicable Concentration Range
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0.032 - 100 mg-S2-/L |
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Interferences
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Humic substances may interfere with Ag/S-ISE measurements. For highly colored water (high concentration of humic substances), use the method of standard additions to check results. Sulfide is oxidized by dissolved oxygen. Sulfide oxidation may cause potential readings to drift in the direction of decreasing concentration, i.e., to more positive values. Flush surface of samples and standards with nitrogen to minimize contact with atmospheric oxygen for low-level measurements. Temperature changes may cause potentials to drift either upward or downward. |
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Quality Control Requirements
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See Section 4020 Quality Assurance/Quality Control. |
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Sample Handling
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Collect water samples with minimum aeration. Either analyze samples immediately after collection or preserve with zinc acetate solution for later analysis. To preserve a sample for a total sulfide determination put zinc acetate and sodium hydroxide solutions into sample bottle before filling it with sample. Use 0.2 mL 2M zinc acetate solution per 100 mL sample. Increase volume of zinc acetate solution if the sulfide concentration is expected to be greater than 64 mg/L. The final pH should be at least 9. Add more NaOH if necessary. Fill bottle completely and stopper. |
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Maximum Holding Time
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28 days; 7 days for regulatory use (See Section 1060) |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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