Optimization of the evaporation cavity in a torch integrated sample introduction system based ICP-AES system. Applications to matrix and transient effects, analysis of microsamples and analysis of certified solid samples

Abstract

Results corresponding to the optimization of the aerosol evaporation cavity of the previously published torch integrated sample introduction system (TISIS) are shown in the present work. A micronebulizer (i.e., MicroMist) operated at liquid delivery rates in the 20–200 µl min⁻¹ range was used throughout. Theoretical calculations suggested that the TISIS chamber allowed the evaporation of a significant fraction of the solvent contained in primary aerosol, while the remaining droplets first impacted against its inner walls and then evaporated. The cavity dimensions (i.e., length and inner diameter) were optimized in terms of sensitivity and memory effects. The results demonstrated that the longer the cavity, the higher the sensitivity, whereas an increase in its diameter did not significantly modify the aforementioned parameters. The optimized TISIS cavity, with a conical shaped end, proved to significantly shorten the wash-out times with respect to a double pass spray chamber and a low inner volume cyclonic type one (i.e., a Cinnabar spray chamber). Besides, the TISIS was used for discrete sample introduction of very low sample volumes (i.e., from 0.3 to 32 µl). The peaks found were narrower and higher than those provided by a double pass spray chamber. Matrix effects caused by sodium, acetic acid and ethanol solutions were less severe for TISIS than for the double pass and the Cinnabar spray chambers, while transient effects caused by nitric acid solutions almost disappeared when using the TISIS. As a result of the mitigation of the interferences, the recoveries found for three certified solid samples while calibrating with plain water standards were closer to 100% for the TISIS than for double pass and mini cyclonic spray chambers.