Time-resolved studies of particle effects in laser ablation inductively coupled plasma-mass spectrometry

Transient signal responses for ablated samples as a function of particle size and laser parameters are characterized. Data are acquired with time resolution of 5 or 6 ms per data point. Large positive spikes in signal are observed and increase in both amplitude and frequency with increasing particle size. Particle sizes are selected using a differential mobility analyzer. Spikes in the signal also increase with decreasing laser rastering rates. A comparison of lasers with pulse widths of 370 fs and 5 ns shows that shortening the pulse width significantly reduces the frequency and amplitude of positive spikes in signal. These large positive spikes are attributed to the vaporization, atomization, and ionization of individual large intact particles, which are considered to be a major cause of fractionation in laser ablation ICP-MS.