The masking of chloride by the use of a HgSO4:Cl ratio of 20:1 prior to digestion, and the use of 3 g K2Cr2O7/L in the digestion solution resulted in an error of less than 10% and 12% for samples containing
40 g NaCl/L at 20–190 mg COD/L and 230 mg COD/L, respectively.