Abstract

The influence of electrical interference induced by the easily ionized sodium matrix upon the laser-enhanced ionization (LEI) detection of indium analyte is studied. A flow injection analysis (FLA) system is interfaced to an LEI apparatus to handle the sample introduction. With the use of FIA-LEI apparatus, as shown in Fig. 1, the electrical interference may be effectively diminished. A significant LEI signal of trace In sample can be resumed in a solution with Na matrix beyond the threshold level, at which no conventional LEI signal is detectable. Figure 2 shows that the In LEI signal is completely suppressed electrically with addition of 2 ppm Na, while our design FIA-LEI apparatus may resist the Na interference more than 40 ppm (Fig. 3).¹ In the FIA-LEI design, a segment of distilled water flow is injected into the carrier stream of sample solution; the mixed solution is then nebulized into the flame. The resulting dilution gradient leads to appearance of a double-peak LEI signal, as shown in Fig. 4. In this work, we employed a single-tank model to satisfactorily describe the total dispersion effect involved in the FIA-LEI system. The relationship between the LEI response and the electrical interference may also be well interpreted in terms of the concept of ion sheath.² Taking into account the dispersion behavior 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 FIA-LEI signal (Fig. 5) and characterize the feature of double-peak profile observed.³ Accordingly, the essence of FIA-LEI apparatus as a tool to reduce the electrical interference may be deeply understood, as is helpful to make the best use of this new design.

© 1995 IEEE