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METHOD 415.3 - MEASUREMENT OF TOTAL ORGANIC CARBON, DISSOLVED ORGANIC CARBON AND SPECIFIC UV ABSORBANCE AT 254 NM IN SOURCE WATER AND DRINKING WATER
Potter, B B. AND J. C. Wimsatt. METHOD 415.3 - MEASUREMENT OF TOTAL ORGANIC CARBON, DISSOLVED ORGANIC CARBON AND SPECIFIC UV ABSORBANCE AT 254 NM IN SOURCE WATER AND DRINKING WATER. U.S. Environmental Protection Agency, Washington, DC, 2005.
Establish optimum performance criteria for current TOC technologies for application to Stage 2 D/DBP Rule.
Develop a TOC and SUVA (incorporating DOC and UV254) method to be published in the Stage 2 D/DBP Rule that will meet requirements as stated in the Stage 1 D/DBP Rule (Revise Method 415.3, "Measurement of Total Organic Carbon, Dissolved Organic Carbon and Specific UV Absorbance at 254 nm in Source Water and Drinking Water", to include additional ruggedness data, method study data, and a combustion TOC procedure).
Investigate the cause for instrument response differences as observed between different kinds of TOC instrument systems.
Develop a method procedure that will control and/or eliminate the cause of TOC instrument response differences.
Revise Method 415.3 Quality Control section to include additional controls for the minimization and/or the elimination of instrument response differences.
Publish Method 415.3 and document in a journal article the development of the method.
2.0 SUMMARY OF METHOD
2.1 In both TOC and DOC determinations, organic carbon in the water sample is oxidized to form carbon dioxide (CO2), which is then measured by a detection system. There are two different approaches for the oxidation of organic carbon in water samples to carbon dioxide gas: (a) combustion in an oxidizing gas and (b) UV promoted or heat catalized chemical oxidation with a persulfate solution. Carbon dioxide, which is released from the oxidized sample, is detected by a conductivity detector or by a nondispersive infrared (NDIR) detector. Instruments using any combination of the above technologies may be used in this method.
2.2. Setteable solids and floating matter may cause plugging of valves, tubing, and the injection needle port. The TOC procedure allows the removal of settleable solids and floating matter. The suspended matter is considered part of the sample. The resulting water sample is then considered a close approximation of the original whole water sample for the purpose of TOC measurement.
2.3. The DOC procedure requires that the sample be passed through a 0.45 um filter prior to analysis.
2.4. The TOC and DOC procedures require that all inorganic carbon be removed from the sample before the sample is analyzed for organic carbon content. If the inorganic carbon (IC) is not completely removed, significant error will occur. The inorganic carbon interference is removed by converting the mineralized IC to CO2 by acidification and sparging with an inert gas to remove the generated CO2. The sample, which is now free from IC interference, is then injected into a TOC instrument system. The orgnaic carbon is oxidized to CO2 which is released from the sample, detected, and repoted as mg/L or ppm TOC or DOC.
2.5. The UVA procedure requires that the sample be passed through a 0.45 um filter and transferred to quartz cell. It is then placed in a spectrophotometer to measure the UV absorbance at 254 nm and reported in cm -1.
2.6. The SUVA procedure requires both the DOC and UVA measurement. The SUVA is then calculated by dividing the UV absorbance of the sample (in cm -1) by the DOC of the sample (in mg/L) and then multiplying by 100 cm/M. SUVA is reported in units of L/mg-M. The formula for the SUVA may be found in Section 12.2.