Novel setup for investigation of the plasma conditions in direct sample insertion inductively coupled plasma atomic emission spectrometry (DSI-ICP-AES)

Abstract

Insertion of a sample probe into the inductively coupled plasma (ICP) for direct sample insertion (DSI) could change the plasma excitation conditions. In this study, a novel setup is proposed for the investigation of the probe effects. A hollow graphite tube was used as a stand-in for the DSI sample probe to exert probe effects on the plasma. Laser-ablated testing elements (Fe, Zn and Mg) were introduced separately into the central channel of the plasma via the hollow graphite tube for measurement of plasma excitation temperature and electron number density. A relatively low Ar carrier gas flow rate (0.42 L min 21 ) was used to minimize perturbation to the plasma due to the gas flow. The study shows that the extent of reduction in plasma excitation temperature and electron number density increases with probe insertion position at all observation heights. In addition, the probe effects strongly depend on the relative distance of the observation position to the tip of the probe. The probe effects are the strongest near the tip of the probe and reduce at observation positions further away from the tip. Signal-to-background ratios (SBR) of the testing elements also depend strongly on the probe insertion position and the relative distance of the observation position to the tip of the probe. The SBR peaks at 5-10 mm above the tip of the sample probe. The vertical profile of SBR depends on analyte diffusion in the plasma and the plasma excitation conditions.

Atomic Spectroscopy

“…The potential of quadrupole ICPMS was studied as an alternative to X-ray spectrometry for the measurement of 129 I in environmental samples by Bienvenu et al (189). Although ICPMS exhibits attractive features for the measurement of this radionuclide, the occurrence of natural iodine 127 I at substantial levels in the solutions recovered after dissolution and extraction steps was shown to induce an interference on the 129 I signal, due to the formation of a polyatomic IH 2 species, as well as a substantial matrix effect for quantitative analyses.…”

“…These difficulties were overcome by analyzing diluted solutions and using 133 Cs as internal standard. The use of ICPMS after sample pretreatment allowed detection limits for 129 I in the range of 10 -4 Bq/g (10 -11 g/g). The accuracy of the measurements was estimated in comparison with results obtained on the same samples by X-ray spectrometry.…”

“…Izmer et al (229) presented an improved method for the determination of 129 I in sediments by quadrupole collision cell ICPMS. The hot extraction of iodine from environmental samples and on-line introduction of analyte via the gas phase into the ICPMS was equipped with a cooling finger, which allowed intermediate iodine enrichment and improved the detection limits for 129 I down to 0.4 pg g -1 without additional sample preparation. A mixture of oxygen and helium as reaction gases in the hexapole collision cell was used for minimizing interferences caused by 129 Xe + .…”

“…The hot extraction of iodine from environmental samples and on-line introduction of analyte via the gas phase into the ICPMS was equipped with a cooling finger, which allowed intermediate iodine enrichment and improved the detection limits for 129 I down to 0.4 pg g -1 without additional sample preparation. A mixture of oxygen and helium as reaction gases in the hexapole collision cell was used for minimizing interferences caused by 129 Xe + . The developed analytical method was applied for 129 I determination at the ultratrace level and for isotope ratio measurements of 129 I/ 127 I down to 10 -7 in contaminated sediments and in Ocean Sediment reference material.…”

Atomic spectrometry update. Advances in atomic emission, absorption and fluorescence spectrometry, and related techniques

“…Cheung et al 216 have reported on the use of a hollow graphite tube as a surrogate for a direct sample insertion (DSI) probe in order to study the effects of DSI on plasma excitation. They found that T exc and n e increased on probe insertion, with the effect being strongest near the tip.…”