EPA-NERL: 375.2: Sulfate by Colorimetry
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Official Method Name
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Sulfate (Colorimetric, Automated, Methylthymol Blue, AA II) |
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Current Revision
| Revision 2.0, August 1993 |
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Media
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WATER |
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Instrumentation
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Automated Spectrophotometer |
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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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A sample is first passed through a sodium form cation-exchange column to remove multivalent metal ions. The sample containing sulfate is then reacted with an alcohol solution of barium chloride and methylthymol blue (MTB) at an acidic pH to form barium sulfate. The combined solution is raised to a basic pH so that excess barium reacts with MTB. The uncomplexed MTB color is gray; if it is all chelated with barium, the color is blue. Initially, the barium and MTB are equimolar and equivalent to 300-mg SO4/L; thus the amount of uncomplexed MTB is equal to the sulfate present. The amount of sulfate in the sample is measured by measuring the absorbance of uncomplexed MTB using a spectrophotometer. |
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Scope and Application
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This method determines sulfate in drinking, ground and surface water; domestic and industrial wastes.
The applicable range is 3-300 mg SO4/L. The sensitivity of the method can be increased by a minor modification to analyze samples in the range of 0.5-30 mg SO4/L. Approximately 30 samples per hour can be analyzed. |
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Applicable Concentration Range
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3 - 300 mg/L and 0.5 - 30 mg/L (with minor modification) |
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Interferences
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(A) Ion exchange column breakdown: Run sulfate/Ca+2standard to ensure proper column operation. (B) Turbidity: Filter or centrifuge turbid samples. (C) Contamination: Reagents or glassware can be contaminated. |
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Quality Control Requirements
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The minimum recommended quality control requirements include an initial demonstration of laboratory capability (determining the linear calibration range and method detection limit, and analyzing a quality control sample; LCR and MDL, and QCS), and the periodic analysis of a laboratory reagent blank. |
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Sample Handling
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Samples should be collected in plastic or glass bottles. All bottles must be thoroughly cleansed and rinsed with reagent water. Volume collected should be sufficient to insure a representative sample, allow for replicate analysis (if required), and minimize waste disposal.
No chemical preservation required. Cool sample to 4 deg. C. Samples should be analyzed as soon as possible after collection. If storage is required, samples maintained at 4 deg. C may be held for up to 28 days. |
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Maximum Holding Time
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28 days (MCAWW, Table 1). |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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