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Methods for the Examination of Water and Wastewater Method 5310).


Conclusion


TOC analysis attempts to measure carbon con- tained in organic molecules and report results as a single value. The value obtained is dependent on the oxidation technique and no single oxida- tion technique is adequate for every purpose. While HTCO has higher oxidation efficiency, the smaller sample volumes introduce sampling error at concentrations below about 1.0 mg/L of carbon; the lower oxidation efficiency of chemi- cal methods is offset by the ability to digest fairly large sample volumes. Thus, when HTCO and chemical oxidation results are compared, even though HTCO results trend higher than chemical oxidation, the results always seem to lie within each other’s experimental error. Figure 3 shows a comparison of chemical oxida- tion and HTCO in drinking water samples. The optimum choice of analyzer should always be made based on the intended application and required sensitivity levels. For lower detection levels, a method utilizing larger sample vol- umes (chemical oxidation) should be chosen. For carbon levels above 1.0 mg/L, the choice of oxidation technique is not so obvious.


Often mentioned but rarely defined, difficult- to-optimize compounds include humic acids, cellulose, alkaloids, large-chain surfactants and bacteria. If these compounds are known to exist in concentrations greater than 1.0 mg/L, then HTCO is the obvious choice of analyzer. If, however, they exist at lower concentrations, then partial recovery is better than no detec- tion at all and a chemical oxidation method should be used.


References


1. Menzel, D.W. and Vacarro, R.F. The mea- surement of dissolved organic and partic- ulate carbon in seawater. Limnology and Oceanography 1964, 9, 138–42.


2. Wilson, R.F. Measurement of organic car- bon in seawater. Limnology and Oceanogra- phy 1961, 6, 259–61.


3. Ehrhard, M. A new method for the auto- matic measurement of dissolved organic carbon in sea water. Deep Sea Research and Oceanography Abstracts 1969, 16(4), 393–7).


Aurora 1030 TOC Analyzer


4. Cauwet, G. Automatic determination of dissolved organic carbon in seawater in the sub-ppm range. Marine Chemistry June 1984, 14(4), 297–306.


5. Sugimara, Y. and Suzuki, Y. A high-temperature catalytic oxidation method for the determination of non-volatile dissolved organic carbon in seawater by direct injection of a liquid sample. Marine Chemistry June 1988, 24, 105–31).


William Lipps is environmental/chemical business unit manager, Shimadzu Scientific Instruments, Inc., 7102 Riverwood Dr., Columbia, Md. 21046, U.S.A.; tel.: 410-381-1227, ext. 1802; e-mail: wclipps@ shimadzu.com; www.shimadzu.com


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AMERICAN LABORATORY 15 MAY 2016


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