AUTOMATIC-DETERMINATION OF OPTIMUM DILUTION LEVELS FOR LASER-ENHANCEDIONIZATION DETECTION OF MATRIX-INTERFERED SAMPLE BY FLOW-INJECTION

A flow injection (FI) system is interfaced to laser-enhanced ionizatio n (LEI) apparatus to handle the sample introduction, With the use of F I-LEI apparatus, the electrical interference induced by the matrix may be effectively diminished, A significant LEI signal of trace In is re covered in a solution containing an Na-matrix concentration greater th an the threshold level, 4-10 ppm (mu g ml((-)1)) in our conditions; at which no conventional LEI signal is detectable. The dilution gradient , resulting from injection of a water plug into the carrier stream of sample solution, leads to the appearance of a double-peak LEI signal, By taking into account the dispersion behaviour of sample solution and the ion-sheath effect, we are able to derive an explicit formula, Acc ording to the formula,me may successfully predict the measured intensi ty of the FI-LEI signal and characterize the features of the double-pe ak observed.