Standard Methods: 4500-O3 B:  Ozone by Indigo Colorimetric Method

  • Summary
  • Analytes
  • Revision
  • Data and Sites
Official Method Name
4500-O3 B. Indigo Colorimetric Method
Current Revision
Standard Methods 21st Edition (2005); Standard Methods Online
Media
WATER
Instrumentation
Spectroscopy (Colorimetry; Photometry)
Method Subcategory
Inorganic
Method Source
  Standard Methods
Citation
  Standard Methods Online - Standard Methods for the Examination of Water and Wastewater
Brief Method Summary
In acidic solution, ozone rapidly decolorizes indigo. The decrease in absorbance is linear with increasing concentration.
Scope and Application
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.
Applicable Concentration Range
Interferences
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.
Quality Control Requirements
See Section 4020 Quality Assurance/Quality Control.
Sample Handling
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.
Maximum Holding Time
0.25 hour
Relative Cost
$51 to $200
Sample Preparation Methods