AOAC: 973.52B: Hardness of Water
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Official Method Name
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Hardness of Water by EDTA Titrimetric Method |
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Current Revision
| 15th Edition (1990) |
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Media
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WATER |
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Instrumentation
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Titration |
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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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Ca and Mg at pH 10 in presence of dye eriochrome black T are wine red. When completely complexed with EDTA, solution becomes blue. Mg must be present for satisfactory end point and is added as MgEDTA. End point sharpness increases with pH, but high pH may cause precipitation of Ca(OH)2 or Mg(OH)2 and cause color changes of dye. pH of 10.0 +/- 0.1 is satisfactory compromise. Limit of 5 min for titration minimizes precipitation. Heavy metal interference is minimized by complexing with cyanide. |
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Scope and Application
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Applicable to drinking water, surface water, and domestic and industrial wastewaters. |
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Applicable Concentration Range
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None given. |
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Interferences
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Not specified in method. |
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Quality Control Requirements
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Not Included |
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Sample Handling
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No information given. |
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Maximum Holding Time
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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