SOME ASPECTS OF THE USE OF HETEROPOLY ANIONS IN ELEMENTAL ANALYSIS BYSIMPLE POTENTIOMETRIC ION-PAIR FORMATION-BASED TITRATION

The possibility of the use of heteropoly anions formed by addition of phosphate to the solutions of either molybdate or tungstate in the det ermination of phosphorus by the simple method of potentiometric titrat ion was studied. The heteropoly anions are titrated on the ion-pairing principle using a titrant containing a lipophilic counter-ion, i.e. 1 -(ethoxycarbonyl)pentadecyltrimethylammonium bromide (Septonex), the t itration bring monitored by carbon paste electrode, although other liq uid membrane-based electrodes can also be used. Calibration plots of t he titrant end-point consumption vs, concentration are not linear, but allow one to evaluate the content of phosphorus. Similar procedures, when optimized, should be elaborated for determination of numerous oth er elements forming heteropoly anions. (C) 1998 Elsevier Science B.V. All rights reserved.