A novel detection scheme of trace elements using ICP-MS

Abstract

A novel sample modulation method for inductively coupled plasma mass spectrometry (ICP-MS) is presented. Analyte ions (Ba, Cd and La) are spatially concentrated onto Fe(OH)3 particles of size of 102 nm. The particles in the original aliquot were introduced into ICP-MS for time-resolved measurement. The spatially concentrated analyte ion on each Fe(OH)3 particle produces a plume of gaseous analyte ions in the ICP. The plume is detected as a current spike in the mass spectrometer. Time-resolved measurement using the time-resolved analysis (TRA) mode of the ICP-MS and a digital oscilloscope showed ICP-MS current spikes corresponding to the preconcentrated analyte of original concentration of 1 pg mL−1 to 1 ng mL−1. The full width at half maximum (FWHM) of the current spikes of the adsorbed analyte is of the same order of magnitude as that of the Fe(OH)3 particles. Enhancement in signal-to-background ratio by the spatial preconcentration–sample modulation method enables the detection of ultra-trace metal (<pg mL−1) using ICP-MS. The detection limit of Ba is 0.05 pg mL−1. Using ICP-MS TRA measurement, the log–log plot of the sum of spike intensity of Ba in a Ba–Fe(OH)3 mixture versus Ba concentration is linear from 1 to 100 pg mL−1. A novel method to generate the Fe(OH)3 particles by spraying Fe(NO3)3 solution onto a basic receiving solution is also presented.