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The coulometric determination of chemical oxygen demand
Author(s) -
Pamplin Kim L.,
Johnson Dennis C.
Publication year - 1997
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/elan.1140090403
Subject(s) - coulometry , chemistry , chemical oxygen demand , reagent , electrolysis , electrolyte , analytical chemistry (journal) , chromatography , electrochemistry , wastewater , electrode , organic chemistry , waste management , engineering
Abstract The chemical oxygen demand ( COD ) of solutions containing various organic compounds is calculated from the net faradaic charge ( Q net ) estimated for the total electrolytic oxidation of Cr III generated during oxidative degradation of the organic compounds in acidic media containing excess Cr VI . Values of Q net for conversion of Cr III to Cr VI are estimated from the linearized chronoamperometric data plotted as In { i tat, t } vs. t . This procedure is preferred over determinations of Q net from the total integrals of i tot over the entire electrolysis period because of large errors that can result from uncertainty in the background current ( i bkg ) for t → ∞. The proposed coulometric procedure offers the benefit that reagent solutions can be reused, thereby minimizing the need for disposal of wastes containing toxic Cr VI . This procedure was applied in a single digest solution for consecutive determinations of COD . Average COD values for potassium acid phthalate and glucose were 103.8% ( s ‐ 6.0, N ‐ 10) and 100.2% ( s ‐ 4.2, N ‐ 11), respectively, based on the theoretical degradation to CO 2 . In comparison for these same samples, an EPA approved method, based on colorimetric determination of Cr III , gave COD values of 101.4% ( S ‐ 1.4, N ‐ 5) and 100.1% ( s ‐ 1.4, N ‐ 5) of the theoretical. Statistical tests indicate no significant difference in the COD values determined for these compounds using the coulometric and EPA methods.