Any method that attempts to determine chemical oxygen demand (COD) by strong wet oxidative means in saline wastes encounters the problem of chloride interference. Chloride oxidation can be avoided by using mild oxidizing conditions but only at the expense of inefficient oxidation of organic matter. The standard procedure ( I ) for the determination of COD by the dichromate reflux method utilizes acid concentrations and heating times which will oxidize roughly 85-95’70 of the organic matter present but will also oxidize essentially 100% of the chloride ion (2). In the standard procedure, interference by chloride ion, at moderate concentrations, is largely prevented through the addition of mercuric sulfate to form unionized mercuric chloride (3). The complexing method, as currently practiced, using a weight ratio of HgS04:Cl equal to 1O:l will yield reproducible results at chloride concentrations up to 5,000 mg/l. Problems due to chloride interference arise in wastes of low to moderate COD with chloride concentrations approaching that of sea water.
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