GRAN PLOT TITRATION AND FLOW-INJECTION TITRATION OF SULFATE IN-GROUNDAND DRINKING-WATER WITH A BARIUM ION-SELECTIVE ELECTRODE

The application of a barium ion-selective electrode for the determinat ion of sulfate is reported. Titrations in the batch mode using the Gra n's plot method [1] have been carried out. In the presence of a lithiu m acetate buffer and after the addition of isopropanol it has been pos sible to determine sulfate with a relative standard deviation (RSD) of 1.5%. The concentration range of the samples was 5-400 mg sulfate/l. Interfering ions were separated by cation-exchange. This indirect titr ation constituted the basis of a flow injection titration (FIA titrati on) system for the continuous determination of sulfate. By plotting th e peakwidth vs. the logarithm of the sulfate concentration of the inje cted samples, linear calibration graphs in the range of 50-200 mg sulf ate/l were obtained. In this system, the sample stream was pumped thro ugh an ion-exchange column, mixed with a buffer stream of lithium acet ate and injected in a reagent stream of a BaCl2 solution. The resultin g free Ba(II) concentration was monitored with a barium ion-selective electrode. The content of sulfate in ground and drinking water samples has been determined with a RSD between 1.2% and 1.3%.