Novel sample introduction and measurement strategies for SC-ICP-MS and SP-ICP-MS

Abstract

The research focuses on two areas. A novel sample introduction method based on electrospray of suspension of biological cells has been developed and characterized for single-cell inductively coupled plasma-mass spectrometry (SC- ICP-MS) measurement. Methods to improve the limit of detection (LOD) of single-particle ICP-MS (SP-ICP-MS) were also investigated.

Single-cell ICP-MS is a powerful technique to determine the elemental contents and distribution of a cell population. The current sample introduction method of SC-ICP-MS is based on solution nebulization. Direct analysis of a cell suspension is not feasible because the high ICP-MS background of the nutrient-rich culture medium may mask the ICP-MS intensity spikes of individual cells. Extensive cleanup of the cell suspension by centrifugation and resuspension of the cells in deionized water is needed. The cleanup procedures induce substantial mechanical and osmotic stress on the cells, which is not desirable.

Electrospray is a viable nebulization method of biological cells. The nebulized cells appear to be intact and proliferate normally. In this study, an electrospray device has been developed for preparation-free sample introduction to the ICP. The batch-type electrospray device consists of an electrospray head which is converted from a stainless-steel fountain-pen nib and a cylindrical copper spray chamber. The electrospray head is enclosed in a glass tube and flushed with a gentle stream of CO2 to avoid electrical breakdown of the atmosphere during electrospray. The CO2 sheath gas is combined with the main Ar carrier gas stream for sample introduction into the ICP. Stable electrospray of a few microliters of cell suspension is obtained by applying an electrical potential of +5.5 to +6.5 kV to the nib. The nebulization and transport efficiency of the system is approximately 10%. C. vulgaris, a unicellular green alga, was used as model cells. The sprayed cells were successfully introduced into the ICP. The characteristics and analytical performance of the electrospray-SC-ICP-MS set up will be presented.