Introduction of electromagnetic induction heating technique into on-line chemical oxygen demand determination

A flow injection system incorporating electromagnetic induction heating oxidation for on-line determination of chemical oxygen demand (COD) was proposed. The procedure utilised electromagnetic induction heating instead of conventional reflux heating, with acidic potassium dichromate acting both as an oxidant and as a spectrometric reagent. The elevated temperature and pressure inside the reaction coil contributed to the improvement of on-line sample oxidation, and hence, sample oxidation time was reduced to ca. 8 min (as compared to 2 h required for conventional method). The sampling frequency was 10 h(-1), along with a quantification limit of 4.0 mg L-1 COD and a linear range of 4-200 mg L-1 COD (potassium hydrogen phthalate, r = 0.9958). Relative standard deviation was evaluated to be 3.5% at 100 mg L-1 COD and the results were comparable to those obtained by the standard method.