Improving single particle ICP-TOFMS using a desolvation sample introduction system and collision cell technology

Abstract

Inductively coupled plasma time-of-flight mass spectrometry (ICP-TOFMS) is increasingly used in various disciplines, especially for the characterization of single particles, because it allows truly simultaneous determination of isotopes over full mass range without sacrificing analytical sensitivity (Baalousha et al., 2021; Erhardt et al., 2019; Goodman et al., 2022). In particular, the extremely high time resolution of TOFMS allows us to detect individual mineral dust particles in the water stream obtained from Continuous Flow Analysis of Greenland Ice cores. Even though collision cell technology (CCT) and high-sensitivity sample introduction have been applied to the ICP-MS systems to overcome analytical limitations in spectral interferences and sensitivity (Burger et al., 2019; Lin et al., 2019), the impact of CCT and high-sensitivity desolvation sample introduction on analysis of single particles, unlikely to bulk analysis, are still relatively poorly understood. We investigated the effects of CCT and high-sensitivity desolvation sample introduction (individually and in combination) on the capability of single particle (sp) ICP-TOFMS including sensitivity and transport/transmission efficiency. To do so, we systemically investigated differences in the sensitivity of total Au, the transport efficiency of Au nano particles as well as the signal amplitude above the background of these nano particles. Application of the desolvation unit without CCT led to a significant improvement of the transport efficiency (number of particles introduced into the plasma) by a factor of about 5 but to a reduction of sensitivity (counts per particle) by about 30 percent. When CCT was used for sp-ICP-TOFMS without the high-sensitivity sample introduction system, the sensitivity for gold ion in particle signals increased by only about six percent. This is similar to the sensitivity improvement for gold ions in dissolved background signals from the ion focusing effect after the collision cell. However, when CCT was used in combination with the high-sensitivity sample introduction system, the sensitivity for gold ion in particle signals increased by another up to about 33 percent compared to the desolvation system without CCT. This could be because the collisional ion focusing is more effective under the high sample transport condition of the high-sensitivity sample introduction system. In conclusion, the high-sensitivity sample introduction system increased the number of detected particles by about 5 times while drying the sample and applying CCT enhanced the sensitivity of analyte ions in the ion optics of sp-ICP-TOFMS by about a third for gold particle signals and a factor of 2 for multi-elemental dissolved background signals. These enhancements will help us to analyze trace isotopes in ice core mineral dust particle analysis and to characterize the chemical composition of detected particles by sp-ICP-TOFMS.