New torch design with an in-built chamber for liquid sample analysis by ICP-AES

Abstract

The analytical performance of the torch integrated sample introduction system (TISIS) for the analysis of very low sample volumes by ICP-AES is described. The TISIS consists of a commercially available torch with a low inner volume cavity (i.e., 5–9 cm³) placed at its base, which is attached to the shortened plasma injector tube through a special PTFE adapter. The nebulizer is vertically fitted to the torch base by means of a home-made Teflon adapter that has an exit for the drain solution. The aerosol is thus generated at the base of the TISIS cavity. The nebulization conditions corresponded to very low liquid flow rates (i.e., from 5 to 200 µl min⁻¹) and conventional gas flow rates (i.e., 0.7 l min⁻¹). Based on previously published work, these nebulization conditions favored aerosol solvent evaporation. At ambient temperature and below 40 µl min⁻¹, almost all the solvent was evaporated and no drain was needed. Therefore, the main purpose of the TISIS cavity was to promote efficient solvent evaporation (instead of selecting the maximum drop size introduced into the plasma) and to simplify the transport path. In order to enhance solvent evaporation, the primary aerosols must be as fine as possible. In the present work, two pneumatic micronebulizers were employed: a so-called high efficiency nebulizer (HEN) and a MicroMist. For the sake of comparison, the HEN was coupled to a double-pass spray chamber and the MicroMist to a cyclonic type spray chamber. The results indicated that the TISIS exhibited promising behavior in ICP-AES, giving rise to emission intensities similar to or higher than both conventional reference systems. No further deterioration of the plasma thermal characteristics was observed when using the TISIS with respect to conventional chambers. The signal stability and limits of detection were similar for the different systems employed.