Selective laser-induced ionization in inductively coupled plasma mass spectrometry

Abstract

Laser-induced ionization was performed in an inductively coupled plasma (ICP) with mass spectrometric detection to improve elemental selectivity through a combination of optical spectroscopic and mass selectivity. The technique was demonstrated using selective ionization of Sr by both resonance ionization spectroscopy and laser-enhanced ionization. A modified commercial ICP-MS system, capable of synchronized gated detection of the ion pulses generated by excimer-pumped dye lasers, was used for this work. The nebulizer flow of the ICP was adjusted to 1.75 l min^–1 in order to enhance the population of neutral Sr atoms. An enhancement in the Sr⁺ ion signal was observed following each pulse of the laser. This enhancement lasted for approximately 0.25 ms and peaked 0.2 ms after the laser pulse at a value of 11% relative to the Sr⁺ ion signal due to the plasma ionization alone. The laser-induced signal is limited by the high degree of direct plasma ionization and ion–electron recombination of laser-produced ions.