Improving the sensitivity of a multi-collector inductively coupled plasma mass spectrometer via expansion-chamber pressure reduction

In this work, we improved the sensitivity of a multi-collector-inductively coupled plasma mass spectrometry system by increasing the vacuum of the expansion chamber using a high-speed EH mechanical booster pump (EH500, 500 m(3) h(-1), BOC Edwards) in conjunction with a standard E2M80 pump (80 m(3) h(-1), BOC Edwards). The vacuum was improved from 1.0 mbar to less than 0.5 mbar. The sample ion yield for heavy isotopes, such as those of Pb, was improved from 0.047% to 0.072% in the wet-plasma mode (sample uptake rate, 113 mu L min(-1)), and from 1.35% to 1.84% in the dry-plasma mode (sample uptake rate 105 mu L min(-1)); the variation in the background intensity was less than 1.3 mV for all the Faraday cups. Thus, the sample ion yield in the wet-plasma mode was enhanced more effectively than that in the dry-plasma mode owing to a slightly larger orifice in the wet cone setup. The accuracies for all the isotopes tested, including those of non-traditional metal ones, in both modes were identical to previously published data within an error of 2 s. These results indicate that improving the vacuum at the interface has no effect on the accuracy of isotope measurements and is an effective method for improving the detectability of isotopic compositions for bulk solution analysis with low element contents and the spatial resolution for measurements performed using the laser-ablation sampling technique. This work could provide an alternative for laboratories with a similar device, when tackling samples with low contents.