EPA-NERL: 130.1: Total Hardness by Spectrophotometer
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Official Method Name
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Hardness, Total (mg/L as CaCO3) (Colorimetric, Automated EDTA) |
|---|---|
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Current Revision
| Issued 1971 |
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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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The magnesium EDTA exchanges magnesium on an equivalent basis for any calcium and/or other cations to form a more stable EDTA chelate than magnesium. The free magnesium reacts with calmagite at a pH of 10 to give a red-violet complex. Thus, by measuring only magnesium concentration in the final reaction stream, an accurate measurement of total hardness is possible. |
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Scope and Application
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This automated method determines the hardness of drinking, surface, and saline waters. Approximately 12 samples 3 per hour can be analyzed. |
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Applicable Concentration Range
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10-400 mg/L |
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Interferences
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None. |
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Quality Control Requirements
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None. |
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Sample Handling
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Cool to 4oC, add HNO3 until sample pH is less than 2. |
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Maximum Holding Time
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6 months (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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None. |
