Standard Methods: 3500-Ca B: Calcium by EDTA
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Official Method Name
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3500-Ca B. EDTA Titrimetric 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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Titration with Color Indicator |
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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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When EDTA (ethylenediaminetetraacetic acid or its salts) is added to water containing both calcium and magnesium, it combines first with the calcium. Calcium can be determined directly, with EDTA, when the pH is made sufficiently high that the magnesium is largely precipitated as the hydroxide and an indicator is used that combines with calcium only. Several indicators give a color change when all of the calcium has been complexed by the EDTA at a pH of 12 to 13. |
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Scope and Application
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The EDTA titration gives good results for control and routine applications, but for samples containing high P levels (>50 mg/L) only the AA or atomic emission methods are recommended because of interferences encountered with EDTA indicators. |
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Applicable Concentration Range
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Interferences
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Under conditions of this test, the following concentrations of ions cause no interference with the calcium hardness determination: Cu(II), 2 mg/L; Fe (II), 20 mg/L; Fe (III), 20 mg/L; Mn (II), 10 mg/L; Zn (II), 5 mg/L; Pb (II), 5 mg/L; Al (III), 5 mg/L; and Sn (IV), 5 mg/L. Orthophosphate precipitates calcium at the pH of the test. Strontium and barium give a positive interference and alkalinity in excess of 300 mg/L may cause an indistinct end point in hard waters. |
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Quality Control Requirements
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See Section 3020 Quality Assurance/Quality Control. |
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Sample Handling
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Plastic or glass containers. Add HNO3 to pH <2. See Sectio 3010 for more details. |
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Maximum Holding Time
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6 months (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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