MULTICOMPONENT ANALYSIS IN SOLUTION USING PIEZOELECTRIC QUARTZ SENSORS .1. DETERMINATION OF O-CRESOL AND M-CRESOL IN WATER

An array of four piezoelectric crystals, each working at a certain pH, was constructed for the simultaneous determination of omicron- and m-cresol in water. As there are differences in the reaction of omicron- and m-cresol with iodine under different pH conditions and because iodine in water can be adsorbed by quartz sensors coated with silver, the two cresols can be determined when excess of iodine is added to solutions containing the compounds and a crystal array is used to measure the remaining iodine. The data obtained were treated by two calibration techniques: multiple linear regression (MLR) and partial least-squares (PLS). With the use of this array of sensors, collinearity may occur, which affects the regression results. The experiments and computations indicated that better concentration estimates can be obtained with PLS than with MLR and the average relative prediction errors for omicron- and m-cresol in five unknown samples were 10.0% and 4.8%, respectively, with MLR and 5.2% and 3.4%, respectively, with PLS.