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.