Noise identification and sampling frequency determination for precise Pb isotopic measurements by quadrupole-based Inductively Coupled Plasma Mass Spectrometry

Analytical precision of the isotope ratios measured by quadrupole-based ICP-MS is drastically controlled by the lowfrequency noises which originate from nebulisation and vaporisation processes, and from sample introduction systems. The undesirable influence of these latter can be however reduced by choosing efficiently the operating parameters. In the present study, the choice of the stabilisation time necessary in peak jump mode, and the one of the number of sweeps are discussed in the light of noise power spectra obtained with various speeds of the peristaltic pump used as sample introduction system. Obviously, the settings proposed are probably efficient only on our own ICP-MS, but they can be determined without any difficulty on any other equipment, only by following the methodology detailed here. With such guidelines, experimental within-run RSD % were observed following closely those predicted by the counting statistics (∼ 110 %). The isotopic measurements of natural samples (overbank sediments, airborne particulate matter, lichens and rainwater) exhibited fair accuracy and good reproducibility, making highly convenient the use of the ICP-MS, at least in an environmental purpose.