National Water Quality Laboratory

Friday October 19, 2018

USGS Open-File Report 97-380

Methods of Analysis by the U.S. Geological Survey National Water Quality Laboratory — Determination of Nonpurgeable Suspended Organic Carbon by Wet-Chemical Oxidation and Infrared Spectrometry

Mark R. Burkhardt, James A. Kammer, Virendra K. Jha, Peggy G. O'Mara-Lopez, and Mark T. Woodworth


Precision and accuracy results are described for the determination of nonpurgeable suspended organic carbon (SOC) by silver-filter filtration, wet-chemical oxidation, and infrared determination of the resulting carbon dioxide (CO2) used at the U.S. Geological Survey’s National Water Quality Laboratory. An aliquot of raw water is filtered through a 0.45 micrometer silver filter. The trapped organic material is oxidized using phosphotic acid and potassium persulfate in a sealed glass ampule, and the resulting CO2 is measured by an infrared CO2 detector. The amount of CO2 is proportional to the concentration of chemically oxidizable nonpurgeable organic carbon in the sample. The SOC method detection limit for routine analysis is 0.2 milligrams per liter. The average percent recovery is 97.1 percent and the average standard deviation is 11 percent.

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