Analytical characteristics of a high efficiency ion transmission interface (S mode) inductively coupled Plasma mass spectrometer for trace element determinations in geological and environmental materials

摘要

The analytical performance of a high transmission interface (S mode), inductively coupled plasma-quadrupole mass spectrometer (the VGE Plasma Quad 3) was evaluated for multitrace element analysis of geological and environmental materials. The sensitivity; limits of detection (LODs), effect of Ca and Na and other major elements on mass response, background, percentage ~(156)CeO+/~(140)Ce~+, ~(70)Ce~(++)/~(140)Ce~+, and long- and short-term variations were compared with those obtained with the conventional mode (normal mode). Normal mode sensitivities varied from 20 MCPS ppm~(-1) (millions of counts per second per ppm) for ~9Be~+, 70-80 MCPS ppm~(-1) for ~(59)Co~+, 90 for ~(115)ln~+ and 40--50 MCPS ppm-t for the heavy masses. S mode sensitivities were 180 MCPS ppm~(-1), for SgCo~+, 350-380 for ~(115)In+ and 140Ce+, 300 MCPS ppm~(-1) for ~(208)Pb~+, and 150 MCPS ppm~(-1) for 232Th~+ and 238U~+, i.e. enhancements amounting to 7. Three #sigma# normal and S mode LODs-are mainly in the 1-2 and 0.1 ppt range, respectively. S mode LODs are enhanced relative' to the normal mode, for masses > 80 amu, by factors ranging from about 10 to 50. S. mode LODs are depressed relative to normal mode LODs for masses < 50 amu by a factor of 10, and the extent of depression is related linearly to mass. In the high- and mid-mass ranges, backgrounds were about 10. They were not affected by sample composition: at 8 amu the S mode background for real samples amounted to about 20, whereas at 220 amu it amounted to four counts. Sand normal mode percentage ~(156)CeO~+/~(140)Ce~+ and ~(70)Ce~(++)/~(140)Ce~+ ratios were about 1.5, and temporal variations were insignificant. The RSDs of normal and S mode Sr~+, Ag~+ and Pb~+ isotope ratios were about 0.1%, with the exception of S mode ~(208)Pb~+/~(207)pb~+ and ~(208)pb~+/~(206)pb~+ ratios in the presence of NaCI, which were degraded by a factor of about 2. Normal and S mode long-term variations for continuous aspiration of 0.1% NaCI for periods of up to 13 h were mass dependent, varying from 2.5-4% for ~7Li~+ and ~9Be~+ to about 2% for the mid-mass range, increasing slightly to about 3% for high masses. Most of this variation occurred during the first 100-150 rain of the analysis during cone priming. With compensation, normal and S mode long-term RSDs and drift were reduced to 1-2%. These variations indicate that extended periods of S mode analysis can be conducted without periodic recalibration. A calibration procedure, based on spiked HNO3, was validated by analysing spiked NaCI solutions, standard water and geological standard reference material (SRM) solutions with internal standardization using conventional solution delivery and flow injection. The agreement of the S mode data and the certified and literature values for ultratrace elements, including ppt levels of rare earth elements in the water standards, was satisfactory. An important conclusion is that ion sampling effects in the S mode are minimal and that the enhanced ion transmission interface is not only beneficial for microanalysis using laser ablation, but for geological and environmental type solutions as well. Sensitivity. enhancements were preserved and matrix effects were approximately +20% for solutions containing 0.1-0.2% total dissolved salt concentration. These variations were reduced to < 5% with internal Standards matched in mass and ionization potential.