ASTM: D1068D: Iron by Photometric Bathophenanthroline
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Official Method Name
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Standard Test Methods for Iron in Water |
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Current Revision
| 1996 |
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Media
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WATER |
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Instrumentation
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Spectroscopy (Colorimetry; Photometry) |
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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 analysis for BPA-reactive ferrous iron consists of the addition of BPA to a buffered sample which forms a red-colored complex with ferrous iron. The red ferrous complex is extracted from the aqueous solution with n-hexyl or isoamyl alcohol and the intensity of its color is measured. HCl-reactive ferrous iron is determined by the addition of buffer and BPA to a previously acidified sample followed by extraction and measurement of the red ferrous complex. Maximum absorption of the complex occurs at 533 nm, and Beer's law is valid. |
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Scope and Application
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These test methods cover the determination of iron in water. Procedures are given for determining total iron, dissolved iron, and ferrous iron. Undissolved iron may be calculated from the total iron and dissolved iron determinations. |
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Applicable Concentration Range
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40 - 1000 ug/L |
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Interferences
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The metal ions other than ferrous iron which can form a complex with bathophenanthroline are manganese, cadmium, copper, zinc, cobalt, nickel, chromium, and ruthenium. The complexation/extraction is carried out at pH 4.0 to 4.5 in the presence of excess bathophenanthroline to achieve maximum color development with Fe(II) and also to eliminate interferences of competing ions. In acid solution, all competing ions form colorless complexes except ruthenium and cobalt which are yellow, and none except the colorless copper complex are extractable into an organic solvent. In a natural water sample buffered at pH 4, cuprous copper is the only metal ion that could potentially affect the measurement of ferrous iron; both species compete for the complexing agent. However, excess bathophenanthroline is present to complex both the ferrous iron and cuprous copper in the sample. |
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Quality Control Requirements
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Sample Handling
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Collect the sample in accordance with Practice D 1066, Specification D 1192, or Practices D 3370, as applicable. Samples should be preserved with HNO3 or HCl (sp gr 1.42) to a pH of 2 or less immediately at the time of collection. If only dissolved iron is to be determined, the sample shall be filtered through a 0.45-um membrane filter before acidification. |
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Maximum Holding Time
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The holding time for samples can be calculated in accordance with Practice D 4841. If ferrous iron is to be determined, the sample should be analyzed as soon as possible after collection and contact with atmospheric oxygen should be minimized. |
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Relative Cost
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Unknown |
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Sample Preparation Methods
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