NEMI Method Summary

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Method Summary

Method Information	Descriptive Name: Ozone by Indigo Colorimetric Method Official Name: 4500-O3 B. Indigo Colorimetric Method Method Number: 4500-O3 B Revision: Standard Methods 21st Edition (2005); Standard Methods Online
Media	Media: WATER
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 Conc Range
Method Download	This is a proprietary method. Please visit the method owner's site for method documentation
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.
QC 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.
Max Holding Time	0.25 hour
Relative Cost/Effort	$51 to $200
Sample Prep Method(s)

Method 4500-O3 B has 1 analytes associated with it.

Analyte	Detection Level	Bias	Precision	Pct False Positive	Pct False Negative	Spiking Level
Ozone (10028-15-6)	N/A	N/A	N/A

export_analytes

Precision Descriptor Notes	For the spectrophotometric volumetric procedure in the absence of interferences, the relative error is less than 5% without special sampling setups. In laboratory testing this may be reduced to 1%. No data are available for the spectrophotometric gravimetric procedure.
Detection Level Note	2 ug O3/L

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