EPA-NERL: 130.2: Total Hardness of Water by Titrimetry
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Official Method Name
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Hardness, Total (mg/L as CaCO3)(Titrimetric, EDTA) |
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Current Revision
| Issued 1971; Editorial Revision 1978 and 1982 |
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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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Eriochrome Black T (EBT) indicator is added to the sample, and EDTA (ethylenediamine tetraacetate) is titrated into the sample. EBT has a red color in the presence of free calcium and magnesium ions. As EDTA is added to the sample it complexes (sequesters) the ions. In the absence of free calcium and magnesium the EBT will turn blue indicating the endpoint of titration. |
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Scope and Application
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This method determines total hardness in drinking, surface, and saline waters; and domestic and industrial wastes. |
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Applicable Concentration Range
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Method is suitable for all concentration levels. |
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Interferences
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(1) A number of metal ions may cause fading or indistinct end points (Standard Methods 2340C provides a listing of interfering metals and their potential effects). (2) Suspended or colloidal organic matter can interfere with the endpoint. |
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Quality Control Requirements
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not included |
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Sample Handling
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Collect at least a 100 mL sample in either glass or plastic bottles. Preserve samples by adding HNO3 until the pH is < 2. Store samples at 4oC until analysis. Analyze samples within 6 months. |
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Maximum Holding Time
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6 months |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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