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Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory-Determination of methylene blue active substances by spectrophotometry

Mark R. Burkhardt·Pete J. Cinotto·Galen W. Frahm·Mark T. Woodworth·Jeffrey W. Pritt
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Abstract

A method for the determination of methylene blue active substances in whole-water samples by liquid-liquid extraction and spectrophotometric detection is described. Sulfate and sulfonate-based surfectants are reacted with methylene blue to form a blue-colored complex. The complex is extracted into chloroform, back-washed with an acidified phosphate-based buffer solution, and measured against external standards with a probe spectrophotometer. The method detection limt for routine analysis is 0.02 milligram per liter. The precision is plus/minus 10 percent relative standard deviation. The positive bias from nitrate and chloride and U.S. Geological Survey method O-3111-83 for methylene blue active substances is minized by adding a back-washing step.

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Mark R. Burkhardt, Pete J. Cinotto, Galen W. Frahm, Mark T. Woodworth, Jeffrey W. Pritt. 1995. Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory-Determination of methylene blue active substances by spectrophotometry. https://doi.org/10.3133/ofr95189

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