Standard Methods: 4500-O3 B: Ozone by Indigo Colorimetric Method
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Official Method Name
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4500-O3 B. Indigo Colorimetric Method |
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Current Revision
| Standard Methods 21st Edition (2005); Standard Methods Online |
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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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In acidic solution, ozone rapidly decolorizes indigo. The decrease in absorbance is linear with increasing concentration. |
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Scope and Application
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The indigo colorimetric method is quantitative, selective, and simple; it replaces methods based on the measurement of total oxidant. The method is applicable to lake water, river infiltrate, manganese-containing groundwaters, extremely hard groundwaters, and even biologically treated domestic wastewaters. |
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Applicable Concentration Range
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Interferences
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Hydrogen peroxide and organic peroxides decolorize the indigo reagent very slowly. H2O2 does not interfere if ozone is measured in less than 6 h after adding reagents. Organic peroxides may react more rapidly. Fe(III) does not interfere. Mn(II) does not interfere but it is oxidized by ozone to forms that decolorize the reagent. Chlorine also interferes but it can be masked by malonic acid. Bromine, which can be formed by oxidation of Br, interferes (1 mole HOBr corresponds to 0.4 mole ozone.) In the presence of HOBr, an accurate measurement of ozone cannot be made with this method. |
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Quality Control Requirements
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See Section 4020 Quality Assurance/Quality Control. |
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Sample Handling
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React sample with indigo as quickly as possible, because the residual may decay rapidly. Avoid loss of ozone residual to off-gassing during sample collection. Do not run sample down side of flask. Add sample so that completely decolorized zones are eliminated quickly by swirling or stirring. |
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Maximum Holding Time
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0.25 hour |
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Relative Cost
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$51 to $200 |
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Sample Preparation Methods
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