Reduction of Space Charge Effects Using a Three-Aperture Gas Dynamic Vacuum Interface for Inductively Coupled Plasma-Mass Spectrometry

Abstract

A three-aperture gas dynamic vacuum interface for ICP-MS has been developed which reduces the ion current within the ion optics. The effect on performance limitations previously associated with space charge were determined. The gas and ion dynamics within the first stage of the vacuum interface are similar to those of current ICP-MS instruments and allow delineation of the relative effects of space charge in the interface region and within the ion optics. The sensitivity of the instrument to trace elements is similar to that of current commercial instruments. The instrument shows an improvement in the discrimination against low mass ion transmission. It also shows a dramatic improvement in both the magnitude and analyte-ion mass dependence of the signal suppression induced by a high concentration of a heavy concomitant element (Tl). The new design results in more uniform ion kinetic energies as a function of ion mass-to-charge ratio. The performance improvements are ascribed to the reduction of space charge effects resulting from both the reduction of the ion current within the ion optics and the reduction of the mass dependence of the ion kinetic energies. It is concluded that the discrimination against low-mass ions and the magnitude and analyte mass dependence of the signal suppression induced by concomitant heavy elements observed with current ICP-MS instruments derive from space charge effects within the ion optics. These effects are less significant within the first stage of the vacuum interface or within the mass analyzer.

Systematic evaluation of a strontium-specific extraction chromatographic resin for obtaining a purified Sr fraction with quantitative recovery from complex and Ca-rich matrices

“…Digestion of the dental tissues was accomplished by means of a hotplate digestion using a HNO 3 -HCl mixture (2:1) in a closed Savillex vial. After digestion was completed, the sample was evaporated to nearly dry and the residue was taken up in 14 M HNO 3 and diluted with milli-Q H 2 O. This procedure was validated by applying the protocol to $ 0.1 g of the bone certified reference materials NIST SRM 1400 Bone Ash and NIST SRM 1486 Bone Meal, selected in view of the similar matrix composition of bone and dental tissues.…”

“…Strontium was leached from the fluorite samples using 6 M HCl, 32 while for the dissolution of glass samples, a HF-HNO 3 mixture (3:1) was used in a first step, followed by evaporation and redissolution in aqua regia (HCl-HNO 3 3:1) in a second step. 33 After the digestion step, both sample types were evaporated to nearly dry, the residue was taken up in 14 M HNO 3 and diluted with milli-Q H 2 O.…”

“…A number of studies conducted with both quadrupole-based and multi-collector ICP-MS have shown that the instrumental mass discrimination can vary considerably with the sample matrix and that the response of two elements of similar mass to a different matrix may not be sufficiently correlated. [2][3][4][5][6] The matrix-related occurrence of spectral interferences and mass discrimination indicate that accurate and precise measurements of small differences in isotopic composition should preferably be conducted on target elements that have been chemically isolated from the sample matrix.…”

“…15 On the other hand, the capacity factor for Rb is lower at 7 M HNO 3 than at 3 M HNO 3 , 17 so that a more efficient separation of Rb and Sr can be accomplished at 7 M HNO 3 . As both HNO 3 concentrations provide some benefits, it was investigated whether or not a difference in Sr recovery could be established depending on the HNO 3 concentration used.…”

“…As both HNO 3 concentrations provide some benefits, it was investigated whether or not a difference in Sr recovery could be established depending on the HNO 3 concentration used. Hereto, a digest of NIST SRM 1400 Bone Ash was split into two aliquots, where one was diluted to 3 M HNO 3 , and the other to 7 M HNO 3 . An amount of these aliquots, equivalent to 10 mg Sr, was loaded onto a pre-packed (2 mL resin) extraction chromatographic column.…”