Secondary ion mass spectrometry measurements of isotopic ratios: Correction for time varying count rates

Published

January 15, 2005

Author(s)

Kevin Coakley, A M. Leifer, David S. Simons

Abstract

In Secondary Ion Mass Spectrometry measurement systems, the count rate of isotopes may vary in time as a particle is consumed during the analysis. Since only one isotope at a time is measured, this drift can introduce systematic error into the estimate of the ratio of any two isotopes. We correct the measurements for drift by aligning the time series of isotopic pairs using a linear interpolation approach. We estimate an isotopic ratio for each of two cases. In one case the time series of the more abundant isotope is aligned with respect to the time series of the less abundant isotope. In the second case the less abundant isotope is aligned with respect to the more abundant one. We average both of these estimates to get a drift-corrected estimate. We present an analytical formula for the uncertainty of the isotopic ratio which accounts for correlation introduced by interpolation. We also present an approximate hypothesis test procedure to detect and quantify possible temporal variation of the measured isotopic ratio during a single analysis. In a Monte Carlo study, we quantify the performance of our methods for simulated data with complexity typical of experimental data collected.

Citation

Intl. J. Mass Spectrometry

Volume

240

Issue

2

Pub Type

Journals

Keywords

drift correction, interpolation, isotopic ratio, Secondary Ion Mass Spectrometry, temporal variation, uncertainty analysis

Citation

Coakley, K. , Leifer, A. and Simons, D. (2005), Secondary ion mass spectrometry measurements of isotopic ratios: Correction for time varying count rates, Intl. J. Mass Spectrometry (Accessed May 11, 2025)