Application of linear prediction to Fourier transform ion cyclotron resonance signals for accurate relative ion abundance measurements

Pulse ion cyclotron resonance (ICR) time domain signals arising from a mixture of ion species typically do not exhibit the smooth exponential decay one normally observes In FTIR and pulse nuclear magnetic resonance (NMR) time domain signals. This nonexponential decay is caused by a number of factors which leads to a time variation in the relative ion Intensities of the species present and to large errors in the accurate experimental measurement of those relative abundances. If pulse ICR signals of short time duration are used (e.g. the first 1K data points out of a total of 64K data points), the accuracy of the ion abundance measurements is greatly improved. It is shown that the linear prediction (LP) method gives more accurate intensity values for each frequency component of the time domain signal than those obtained from the more standard Fourier transform (FT) method, and for short acquisition times the resolution obtained with LP methods is much greater than for FT. In addition, the intensities determined by LP are much less sensitive to instrument operating conditions. The advantages of LP methods are particularly relevant to laser desorption ICR spectroscopy.