Factors Affecting the Production of Fast Transient Signals in Single Shot Laser Ablation Inductively Coupled Plasma Mass Spectrometry

Abstract

Low sample consumption and high achievable spatial resolution combine to make laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) an attractive direct sampling technique for the analysis of solids. These desirable characteristics are best realized when the laser ablation system is operated in a single-shot fashion, in which each laser pulse produces a transient analyte signal. The temporal width of a single-shot LA analyte transient is inversely related to the best achievable signal-to-noise ratio (S/N). Thus, production of fast transient signals is an important consideration in single-shot LA analyses. In this study we explore the effects on transient pulse width of ablation-cell volume, the diameter and length of tubing used to connect the ablation cell to the ICP, and the composition and flow rate of ablation-cell sweep gas. Minimization of ablation-cell volume and the length and diameter of the transfer tube was found to dramatically decrease the peak widths of transient signals. However, use of helium gas to sweep analyte particles from the ablation cell was found to significantly reduce the effect of cell volume on transient width. Use of a cell volume of 0.70 cm3 and optimization of other instrumental parameters produced a transient sample pulse 85 ms in duration and limits of detection in the tens of femtograms range for single-shot laser-ablation events.

Peer Reviewed: Numerical Simulation of Aerosol Transport in Atomic Spectrometry

“…The corresponding mass flow calculated for a larger ablation cell (volume = 3 cm 3 ) resulted in a dispersion that was 10 times larger. It is interesting that the runs of the mass flow curves are in reasonable agreement with LA-ICPMS data measured recently for ablation cells of a comparable size (17 ). We are currently conducting experiments to verify calculated mass flows, especially for small ablation cells.…”

Peer Reviewed: Plasma Source TOFMS

“…Not surprisingly, S/N is maximized when the dispersion of ablated particles is minimized. In LA-ICP-TOFMS, measured peak widths of ~85 ms fwhm provided optimal S/N and detection limits of 10-200 fg for most elements (33). This approach to multielemental analyses places a premium on the speed of the detection system, making TOFMS particularly attractive.…”

Use of a novel array detector for the direct analysis of solid samples by laser ablation inductively coupled plasma sector-field mass spectrometry*1

“…The pulse repetition rate is selectable between 1 and 20 Hz and the ablation crater can be varied in diameter from 10 to 300 m by means of a ceramic aperture. The ablation cell provided with the system was replaced with one described by Leach and Hieftje [24]. This cell has been designed to provide fast sample washout through use of a low internal volume …”