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

The characteristics of a dynamic reaction cell (DRC), used to reduce interf erences from molecular or elemental ions in an inductively coupled plasma q uadrupole mass spectrometer (ICP-MS), were investigated for dry sample intr oduction. The dependence of the signals from molecular ions formed in the I CP or in the interface region was monitored with the variation of the conce ntration of reaction or buffer gas used. The differences between wet aeroso ls, generated with a standard cyclonic spray chamber and concentric nebuliz er, to dry aerosols, generated by a desolvating nebulizer or laser ablation , were determined. The comparison of prominent background signals to ion si gnals from selected analyte ions was used to determine parameters that lead to optimum signal/background ratios and analytical performance for laser a blation analysis. Ammonia and hydrogen were used as reactive gases in these experiments. Additionally, He, Ne and Xe were used as a buffer gas to enha nce 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 thr ough the formation of clusters, were severe with ammonia. Hydrogen, having a smaller reactivity, reduces cluster formation and retains analyte sensiti vity even at a high gas concentration. It is therefore better suited for me thods that allow only short measurement times, like laser ablation (LA) or electrothermal vaporization (ETV). The capabilities of the DRC for LA are d emonstrated 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 isot ope led to a reduction of the limit of detection for Ca in quartz by two or ders of magnitude and an improvement of accuracy for the determination of N b in a chromium-matrix.