Automatic determination of optimum dilution levels for laser-enhanced ionization detection of matrix-interfered sample by flow injection

Abstract

A flow injection (FI) system is interfaced to laser-enhanced ionization (LEI) apparatus to handle the sample introduction. With the use of FI–LEI apparatus, the electrical interference induced by the matrix may be effectively diminished. A significant LEI signal of trace In is recovered in a solution containing an Na-matrix concentration greater than the threshold level, 4–10 ppm (µg 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. According to the formula, we may successfully predict the measured intensity of the FI–LEI signal and characterize the features of the double-peak observed.