In a number of experiments it was shown that the dithionate ion possesses a
higher effective mobility than the chloride ion in aqueous solution, thus
enabling the direct and simultaneous isotachophoretic determination of chlo
ride and other anions. Using an acid-base titration, we found only one pK(a
) value for dithionic acid, which is in contrast to the two pK(a) values st
ated in the literature. Based on this pK(a) value, theoretical calculations
and the experimentally observed effective mobility of the dithionate ion i
ndicate a higher effective mobility compared to the chloride ion from pH 3.
Taking into account the physico-chemical properties of the dithionate, its
unrestricted use as isotachophoretic leading ion was confirmed. Based on t
he dithionate ion, new electrolyte systems for the determination of chlorid
e were used. One system was optimised for the determination of chloride and
other low-molecular-mass anions and applied to the analysis of waste water
and drinking water. The water samples were analysed in parallel by ion chr
omatography and compared with the isotachophoretic results. (C) 1999 Elsevi
er Science B.V. All rights reserved.