Characteristics and capabilities of an ICP-MS with a dynamic reaction cell for dry aerosols and laser ablation

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Abstract
The characteristics of a dynamic reaction cell (DRC), used to reduce interferences from molecular or elemental ions in an inductively coupled plasma quadrupole mass spectrometer (ICP-MS), were investigated for dry sample introduction. The dependence of the signals from molecular ions formed in the ICP or in the interface region was monitored with the variation of the concentration of reaction or buffer gas used. The differences between wet aerosols, generated with a standard cyclonic spray chamber and concentric nebulizer, to dry aerosols, generated by a desolvating nebulizer or laser ablation, were determined. The comparison of prominent background signals to ion signals from selected analyte ions was used to determine parameters that lead to optimum signal/background ratios and analytical performance for laser ablation analysis. Ammonia and hydrogen were used as reactive gases in these experiments. Additionally, He, Ne and Xe were used as a buffer gas to enhance thermalization in the DRC. The reaction rate with ammonia was found to be distinctly higher than with hydrogen. On the other hand, side reactions with analyte ions, leading to additional interferences and analyte loss through the formation of clusters, were severe with ammonia. Hydrogen, having a smaller reactivity, reduces cluster formation and retains analyte sensitivity even at a high gas concentration. It is therefore better suited for methods that allow only short measurement times, like laser ablation (LA) or electrothermal vaporization (ETV). The capabilities of the DRC for LA are demonstrated through the determination of Ca in a quartz sample and Nb in a chromium matrix, which suffer from either Ar-ions or Ar-based interferences. Reduction of the background intensities and use of the most abundant isotope led to a reduction of the limit of detection for Ca in quartz by two orders of magnitude and an improvement of accuracy for the determination of Nb in a chromium-matrix.