Digestion efficiency study of an intraplasmic reactor for in-situ, halogen assisted direct solid sample digestion by inductively coupled plasma atomic emission spectroscopy

摘要

A new type of intraplasmic reactor designed for in-situ, batch digestion of refractory solid samples, the Modified Direct Sample Introduction (MDSI) reactor, is presented and qualitatively evaluated with CH3Cl, Cl-2 and Freon-12 as gaseous halogenating reagents. A comparison of the digestion capabilities of MDSI and CH3Cl or Freon-12 assisted electrothermal vaporization is also presented. The refractory model compounds used were Al2O3 and SiO2, which were deposited inside the reactor as 10 mu l of a 1% m/m slurry. A soil sample SO-3 CRM was also used to evaluate the detection limits, which were found to be in the ppb range for sensitive lines (Cu and Pb) and in the ppm range for less sensitive lines (Al, Fe, Si and Zn). The results obtained indicate that the MDSI reactor design rapidly achieved a sufficiently high temperature for quantitative vaporization of the samples. The study of the various halogenating reagents show that (1) the presence of carbon in the halogenating reagent acts as a reducing agent for the oxides and also forms a protective pyrolitic graphite coating on the reactor's inner walls, thereby reducing analyte permeation into those walls and (2) the ideal gaseous halogenating reagent must exhibit a good thermal stability to intermediate temperatures (similar to 200 degrees C) to avoid premature decomposition. The reactive intermediates must also be thermally stable to avoid formation of soot that may plug the reactor and reduce the vaporization. Of all reagents tested, Freon-12 remains the reagent of choice for in-situ digestion of refractory solids. (C) 1998 Elsevier Science B.V. [References: 31]