TIME-RESOLVED MEASUREMENTS OF INDIVIDUAL ION CLOUD SIGNALS TO INVESTIGATE SPACE-CHARGE EFFECTS IN PLASMA-MASS SPECTROMETRY

A new approach to directly monitor space charge induced effects due to high concentrations of efficiently ionized elements in inductively co upled plasma mass spectrometry (ICP-MS) is described. The broadening o f ion clouds produced from individual, monodisperse drops of sample is measured by using time-resolved ICP-MS. The extent of broadening due to high concentrations of Pb in the sample is related inversely to the analyte mass. For the lightest analyte investigated, Li+, the relativ e width of the time-resolved analyte peak increases and then shows a d ip in the center as the Pb concentration is increased to 500 and then 1500 mu g/mL. The initial results of experiments that investigated che mical matrix effects as a function of concomitant species concentratio n, analyte mass, and sampling location in ICP-MS are consistent with s pace-charge effects.