Electrothermal vaporization for sample introduction in AAS and plasma spectrometry

Complete text of publication follows. Electrothermal vaporization (ETV) sample introduction of solutions, slurries and solid samples in inductively coupled plasma-optical emission spectrometry (ICP-OES) and -mass spectrometry (ICP-MS) has been applied successfully for the analysis of a variety of samples (M. Resano et al., J. Anal. At. Spectrom., 23 (2008) 1450-1475.). One of the clear advantages is the possibility of matrix removal during the pyrolysis step, similar to what is normal practice in electrothermal atomic absorption spectrometry (ETAAS). Pyrolysis curves are traditionally measured in ETAAS to select the maximum pyrolysis temperature that can be applied to remove most of the sample matrix without loosing the analyte(s) and chemical modifiers are generally used to stabilize the analyte and/or to facilitate matrix removal. Although this approach has also been adopted in ETV sample introduction in plasmas, the situation is more complicated there because the transport of the analytes to the plasma depends on the amount of vaporized substance. Consequently, the degree of removal of the sample matrix may influence the sensitivity (A.F. Silva et al., Spectrochim. Acta Part B, 63 (2008) 755-762.). In ETV-ICP-MS, non-linear calibration curves are frequently observed with low-matrix or matrix-free standard solutions. If chemical modifiers co-vaporize with the analyte, their effect is manifested in increased transport efficiency for the analytes, which can be explained by considering that the vapor of the modifier nucleates to a higher extent than the analyte vapor and the latter can condense onto the modifier nuclei. In addition to this, chemical condensation can also be the case with complex matrices when a less volatile compound is formed by a chemical reaction in the vapor phase. Optimization of the temperature program for ETV-ICP-MS work is therefore more complicated than the traditional optimization of the temperature program in ETAAS. Due to the somewhat higher analyte concentrations used in ETV-ICP-OES, the situation is less critical. A variety of pyrolysis curves will be presented and discussed. In addition to being a useful technique for solid, slurry and liquid samples, ETV has proven to be a nice tool for the introduction of small sample volumes in the plasma, e.g. in single-drop microextraction methods (S. Gil et al., Spectrochim. Acta Part B, 64 (2009) 208-214.).