Optimization of ETV-ICP(TOF)MS and transient signal profiles for reducing isobaric interferences

Abstract

One of the advantages of the ETV sample introduction is the ability to temporally separate analyte elements in complex mixtures by differences in their vaporization temperatures within the ETV for ICPMS. However, the broadening of the transient peaks in the transport tubing often obscures this temporal resolution. This study shows that decreasing the transport tubing diameter produces little broadening beyond that produced during aerosol production in the ETV. Maintaining such narrow peaks through the transport process to the ICP permits time resolution to circumvent atomic isobaric interferences. Differences in vaporization characteristics of the elements were used to resolve the isobaric overlaps among Zn, Ni, Se, Ge, Cd, In and Sn. A Monte Carlo simulation that focused on particle motion from the ETV to the plasma source was employed to evaluate the roles of diameter of transport tubing and heating rate of the ETV on signal broadening. It was shown that laminar flow broadening was reduced by decreasing the transport tubing diameter and thus more closely reflected the generation function of the ETV. However, for some elements there was as much as a 75% reduction in signal from use of the smaller, 1.5 mm i.d. tubing. There was also a trend to further improve the resolution using lower heating rates of the ETV, although the longitudinal non-isothermality of the graphite furnace broadened the peaks beyond the values expected if there was no gradient along the length of the ETV. This was more noticeable for lower heating rates, e.g., <400 °C s⁻¹. Results are presented for Monte Carlo simulations and time resolved signals obtained on an ETV-ICP(TOF)MS system.