Solid sample introduction by laser ablation for inductively coupled plasma source mass spectrometry
The results are described of a preliminary study of the mass spectrometry of solid samples using a ruby laser to ablate the sample into an inductively coupled plasma (ICP) source mass spectrometer. Standard rock samples were used, pelletted with a binder into the form of a disc. Some 200 ablation pits could be accommodated on each sample. Laser pulse energies of 0.3–1 J were used in the fixed Q mode and the ablated material transferred from the ablation cell into the plasma torch by means of the plasma injector gas flow. The mass spectrometer was used in the fixed ion mode using mean ion current detection to evaluate the reproducibility of successive pulses on major constituents and in the scanning mode at the rate of 10 scans s–1 to produce spectra using mean current detection for major elements and pulse counting detection for traces. Problems were experienced with saturation of the detection system in both the mean current and pulse counting modes owing to the transient nature of the sample pulse from the laser, when attempting to quantify major elements, but except where a major peak was saturated, reasonably uniform sensitivity for most elements across the mass range from 7 to 238 m/z was obtained. Isotope ratio measurements were made on lead at 29 µg g–1 and detection limits for the elements examined appear to be 10 ng g–1 or less.