Effect of temperature on direct chemical vapor generation for plasma optical emission spectrometry: an application of programmable temperature spray chamber

Jacek Giersz , Krzysztof Jankowski

Abstract

A new approach based on a programmable temperature spray chamber (PTSC) is described that extends the analytical capability of a direct chemical vapor generation technique (DCVG) by affecting the sensitivity of measurements by both microwave induced plasma (MIP) and inductively coupled plasma (ICP) optical emission spectrometry. Examination of DCVG process and instrumental conditions was performed to characterize the new approach when coupled with the robust and non-robust argon ICP, and helium or argon low-power MIP. Hence, a real comparison between four examined plasma spectrometry systems may be attained based on determination of hydride-forming elements including As, Se and Sb, and Hg forming atomic vapor as well as iodine forming molecular vapor. All observed trends are discussed and explained so that the influence of analyte vapor generation process on analytical figures of merit clearly may be distinguished from that of the water aerosol and vapor delivery process. The main advantage of the DCVG system based on PTSC is its full compatibility with conventional pneumatic nebulization system used in plasma spectrometric techniques, and the improvement in determination of elements that are released from aqueous solutions as easily volatile species. In order to improve the sensitivity, the PTSC was either cooled at 0 °C in the case of MIP-OES or electrically-heated at 60 °C when coupled with the ICP-OES. For ICP-OES, a slight improvement in sensitivity with increasing temperature was observed due to increased sample delivery rate to the plasma rather than that due to increased analyte vapor generation efficiency. With PTSC, the figures of merit by ICP-OES are improved for all analytes studied comparing with those by ICP-OES with a conventional solution nebulization. The LODs obtained for As, Se, Sb, Hg and I were 5, 5.4, 2.7, 0.085 and 9 μg L−1 , respectively. Concerning DCVG-PN-PTSC-MIP-OES system, a predominant role of the analyte vapor generation efficiency on the analytical performance was found rather than increased analyte transport efficiency. The beneficial effect of the analyte vapor release is enhanced, however, by combination with reduction of the water loading to the plasma by PTSC cooling. The performance of the DCVG-PN-PTSC-He MIP-OES system was evaluated by determining LODs, which are 20, 14, 19, 2.5 and 8 μg L−1 for As, Se, Sb, Hg, and I, respectively.