<?xml version='1.0' encoding='utf-8'?>
<oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
  <dc:contributor>Pete J. Cinotto</dc:contributor>
  <dc:contributor>Galen W. Frahm</dc:contributor>
  <dc:contributor>Mark T. Woodworth</dc:contributor>
  <dc:contributor>Jeffrey W. Pritt</dc:contributor>
  <dc:creator>Mark R. Burkhardt</dc:creator>
  <dc:date>1995</dc:date>
  <dc:description>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.</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.3133/ofr95189</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>U.S. Geological Survey</dc:publisher>
  <dc:title>Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory-Determination of methylene blue active substances by spectrophotometry</dc:title>
  <dc:type>reports</dc:type>
</oai_dc:dc>