CONTINUOUS-FLOW THIN-LAYER HEADSPACE (TLHS) ANALYSIS .4. INDIRECT POTENTIOMETRIC DETERMINATION OF VOLATILE ORGANIC HALOGENS (VOX) IN WATER

The paper presents two methods of potentiometric VOX determination in drinking water utilizing the previously developed TLHS method for the isolation of the volatile analytes from aqueous samples. Halogen mineralization products are converted with the use of silver oxyiodide into iodine equivalent, reduced subsequently to iodide ions using ascorbic acid or sodium sulphite solutions. An iodine ion-selective electrode and Ag/AgI electrodes have been used for the final determination of iodides in the washing solution. Both methods proved to be very precise and accurate, the detection limit being lower in the case of the Ag/AgI electrode (of the order of hundreds of pg/ml). The derived compact form of the general equation describing the recovery of the volatile analyte enabled an easy estimation of the flattening of the recovery curve around the maximum, determining the magnitude of the effect of gas flow rate variations on the accuracy and precision of the determination.