Time-Resolved Inductively Coupled Plasma Mass Spectrometry Measurements with Individual, Monodisperse Drop Sample Introduction

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Abstract
Individual ion clouds, each produced in the ICP from a single drop of sample, were monitored using time-resolved mass spectrometry and optical emission spectrometry simultaneously. The widths of the ion clouds in the plasma as a function of distance from the point of initial desolvated particle vaporization in the ICP were estimated. The Li+ cloud width (full width at halfmaximum) varied from 85 to 272 μs at 3 and 10 mm from the apparent vaporization point, respectively. The Sr+ cloud width varied from 97 to 142 μs at 5 and 10 mm from the apparent vaporization point, respectively. The delays between optical and mass spectrometry signals were used to measure gas velocities in the ICP. The velocity data could then be used to convert ion cloud peak widths in time to cloud sizes in the ICP. Li+ clouds varied from 2.1 to 6.6 mm (full width at half-maximum) and Sr+ clouds varied from 2.4 to 3.5 mm at the locations specified above. Diffusion coefficients were estimated from experimental data to be 88, 44, and 24 cm2/s for Li+, Mg+, and Sr+, respectively. The flight time of ions from the sampling orifice of the mass spectrometer to the detector were mass dependent and varied from 13 to 21 μs for Mg+ to 93 to 115 μs for Pb+.