Non-linear signal response functions and their effects on the statistical and noise cancellation properties of isotope ratio measurements by multi-collector plasma mass spectrometry |
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| Institution: | 1. School of Dentistry, Cardiff University, Heath Park, Cardiff CF14 4XY, United Kingdom;2. Research Unit of Oral Health Sciences, Faculty of Medicine, University of Oulu, Oulu, Finland;3. Medical Research Center Oulu (MRC Oulu), Oulu University Hospital, Oulu, Finland;4. Medical Imaging Research Center, UZ Leuven, 3000 Leuven, Belgium;5. Department of Human Genetics, KU Leuven, 3000 Leuven, Belgium;6. OMFS IMPATH Research Group, Department of Imaging and Pathology, Faculty of Medicine, KU Leuven, Leuven, Belgium;7. Facial Sciences Research Group, Murdoch Children''s Research Institute, Melbourne, Australia;8. Department of Paediatrics, University of Melbourne, Melbourne, Australia;9. Department of Electrical Engineering, ESAT/PSI, KU Leuven, 3000 Leuven, Belgium;1. Department of Environment, Earth and Ecosystems, CEPSAR, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK;2. School of Earth Sciences, University of Bristol, Wills Memorial Building, Queen''s Road, Bristol BS8 1RJ, UK;3. Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ. Paris Diderot, CNRS, F-75005 Paris, France;4. Institut Universitaire de France, France;5. School of Environmental Science and Engineering, Tianjin University, 92 Weijin Road, Nankai District, 300072 Tianjin, PR China;6. Department of Earth Sciences, Durham University, Science Labs, Durham DH1 3LE, UK |
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| Abstract: | A nebulizer-centric response function model of the analytical inductively coupled argon plasma ion source was used to investigate the statistical frequency distributions and noise reduction factors of simultaneously measured flicker noise limited isotope ion signals and their ratios. The response function model was extended by assuming i) a single gaussian distributed random noise source (nebulizer gas pressure fluctuations) and ii) the isotope ion signal response is a parabolic function of the nebulizer gas pressure.Model calculations of ion signal and signal ratio histograms were obtained by applying the statistical method of translation to the non-linear response function model of the plasma. Histograms of Ni, Cu, Pr, Tl and Pb isotope ion signals measured using a multi-collector plasma mass spectrometer were, without exception, negative skew. Histograms of the corresponding isotope ratios of Ni, Cu, Tl and Pb were either positive or negative skew. There was a complete agreement between the measured and model calculated histogram skew properties.The nebulizer-centric response function model was also used to investigate the effect of non-linear response functions on the effectiveness of noise cancellation by signal division. An alternative noise correction procedure suitable for parabolic signal response functions was derived and applied to measurements of isotope ratios of Cu, Ni, Pb and Tl. The largest noise reduction factors were always obtained when the non-linearity of the response functions was taken into account by the isotope ratio calculation.Possible applications of the nebulizer-centric response function model to other types of analytical instrumentation, large amplitude signal noise sources (e.g., lasers, pumped nebulizers) and analytical error in isotope ratio measurements by multi-collector plasma mass spectrometry are discussed. |
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