USGS-NWQL: O-1122-92: Dissolved Organic Carbon in Water by Persulfate Oxidation and Infrared Spectrometry

Summary
Analytes
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Data and Sites

Official Method Name

METHODS OF ANALYSIS BY THE U.S. GEOLOGICAL SURVEY NATIONAL WATER QUALITY LABORATORY - DETERMINATION OF DISSOLVED ORGANIC CARBON BY UV-PROMOTED PERSULFATE OXIDATION AND INFRARED SPECTROMETRY

Current Revision

1992

Media

WATER

Instrumentation

Total Organic Carbon Analyzer

Method Subcategory

Organic

Method Source

USGS-NWQL

Citation

R.W. Brenton and T.L. Arnett, 1993, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory--Determination of dissolved organic carbon by uv-promoted persulfate oxidation and infrared spectrometry: U.S. Geological Survey Open-File Report 92-480

Brief Method Summary

The sample is acidified, purged to remove carbonates and bicarbonates, and the organic carbon is oxidized to carbon dioxide with persulfate, in the presence of an ultraviolet light. The carbon dioxide is measured by nondispersive infrared spectrometry.

Scope and Application

This method is suitable for the analysis of water, brines, and waste water containing at least 0.1 mg/L of dissolved organic carbon (DOC). Samples containing more than 20 mg/L DOC either need to be diluted or have the sample volume reduced. The method is not suitable for the determination of volatile organic constituents.

Applicable Concentration Range

0.1 - 20 (undiluted)

Interferences

Carbonates and bicarbonates usually present in most water are readily converted to carbon dioxide when acidified. Samples must be purged with nitrogen gas to remove carbon dioxide after acidification. Volatile organic compounds are lost during this step. Water samples containing large concentrations of chloride ion will interfere by decomposing the persulfate oxidant and reducing UV excitation energy. This interference becomes significant when chloride concentrations are equal to or greater than 0.1 percent (1,000 mg/L). The American Public Health Association (1989) reports that strongly acidic solutions and some brines interfere with this technique by producing infrared-absorbing aerosols.

Quality Control Requirements

Quality-control samples area analyzed at a minimum of one in every ten samples. These QC samples include at least one of each of the following: blanks, quality control samples, third party check solutions, replicates, and spikes. Correlation coefficients for calibration curves must be at least 0.99. QC samples must fall within 1.5 standard deviations of the mean value. If all of the data-acceptance criteria in the SOPs are met, then the analytical data are acceptable.

Sample Handling

Description: 125 mL Glass bottle, amber. Treatment and Preservation: Bottle baked at 450^oby laboratory. DO NOT RINSE BOTTLE BUT RINSE FILTER WITH ORGANIC-FREE WATER. Filter sample using supor or glass fiber filter (see Lab Code description above for filter type), acidify to pH < 2 with 1 mL of 4.5N sulfuric acid (H₂SO₄), chill and maintain at 4^oC, ship immediately.

Maximum Holding Time

28 days from sampling

Relative Cost

Less than $50

Sample Preparation Methods

This method has 1 analyte associated with it.

Analyte	Detection Level	Bias	Precision	Pct False Positive	Pct False Negative	Spiking Level
Dissolved organic carbon(N-55776) DOC Dissolved organic carbon	0.100 mg/L	N/A	N/A

Precision Descriptor Notes:	Spike samples were prepared by dissolving potassium biphthalate in laboratory distilled water at four different concentrations. Ten replicates of each concentration were analyzed. Single operator precision and recovery information are as follows: for samples with theoretical recovery values of 1.0, 5.0, 15.0 and 20.0 mg/L the mean recoveries were 1.0, 5.0, 14.9 and 19.8 mg/L and 0.07, 0.11, 0.18 and 0.16 mg/L standard deviations with 7.0, 2.2, 1.2 and 0.8 %-RSD, respectively. Five samples from district sites, ranging in DOC content from about 0.3 to about 18 mg/L, were analyzed seven times each to evaluate analytical precision when analyzing natural-water samples. The mean recoveries were 0.3, 2.3, 8.1, 13.7 and 17.9 mg/L and 0.03, 0.11, 0.34, 0.46 and 0.23 mg/L standard deviations with 8.4, 5.0, 4.2, 3.3 and 1.3 %-RSD, respectively.
Detection Level Note:	Method detection limits (MDLs) were determined for this method using the procedures of the U.S. Environmental Protection Agency (1997).

Precision Descriptor Notes:

Spike samples were prepared by dissolving potassium biphthalate in laboratory distilled water at four different concentrations. Ten replicates of each concentration were analyzed. Single operator precision and recovery information are as follows: for samples with theoretical recovery values of 1.0, 5.0, 15.0 and 20.0 mg/L the mean recoveries were 1.0, 5.0, 14.9 and 19.8 mg/L and 0.07, 0.11, 0.18 and 0.16 mg/L standard deviations with 7.0, 2.2, 1.2 and 0.8 %-RSD, respectively. Five samples from district sites, ranging in DOC content from about 0.3 to about 18 mg/L, were analyzed seven times each to evaluate analytical precision when analyzing natural-water samples. The mean recoveries were 0.3, 2.3, 8.1, 13.7 and 17.9 mg/L and 0.03, 0.11, 0.34, 0.46 and 0.23 mg/L standard deviations with 8.4, 5.0, 4.2, 3.3 and 1.3 %-RSD, respectively.

Detection Level Note:

Method detection limits (MDLs) were determined for this method using the procedures of the U.S. Environmental Protection Agency (1997).

Revision	PDF/Link
1992

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USGS-NWQL: O-1122-92: Dissolved Organic Carbon in Water by Persulfate Oxidation and Infrared Spectrometry

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