DISPERSION BEHAVIOR OF CHROMOGENIC REAGENTS IN A MICROWAVE FIELD IN A FLOW SYSTEM - APPLICATION TO THE SPECTROPHOTOMETRIC FLOW-INJECTION DETERMINATION OF PALLADIUM AND RHODIUM

Microwave heating associated with flow-injection (FI) analysis was used to expand the field of application of FI analysis. A laboratory-made microwave-irradiation flow-injection analyser and a chromogenic reagent, 4-(5-chloro-2-pyridylazo)-1,3-diaminabenzene (5-Cl-PADAB), were used to establish an FI spectrophotometric method for the sequential determination of Pd and Rh. The relationship between the dispersion coefficient D of various chromogenic reagents and the microwave irradiation time, t(m), was established as D = a + bt(m)/(t(m) + c), where a, b and c are constants. The relationship between D and the molecular weight M of the solvent (methanol, ethanol, propan-1-ol, propan-2-ol, butan-1-ol and pentan-1-ol) was found to be D = a' + b'M, where a' and b' are constants. The effect of microwave irradiation on the coordination reactions between 5-Cl-PADAB and Pd, Rh, Ru, Os, Ir and Pt was studied.