Novel methods for automatic phase correction of NMR spectra

Abstract

A new and simple algorithm for performing fully automatic phase correction of ( in vivo) NMR spectra with zero-, first-, and even higher-order phase distortions is presented. The method employs the measured phases at the peak positions of spectral lines to calculate the phase distortion. Additionally, two other new methods are discussed. In one method a crude model of the measured spectrum is estimated and deliberately phase-distorted. The phase curve of the spectral model outside the region where the spectral lines are positioned is compared with the phase curve of the measured spectrum over the same regions to iteratively determine the phase distortion. The last method extrapolates the measured time signal to the t = 0 time point. The criterion by which to decide when the applied time shift is correct is derived from the phase curve over the outer regions of the spectrum obtained from this extrapolated time signal. This should be +π/2 at the low-frequency side of the spectral lines and −π/2 at the high-frequency side. The phase distortion is then calculated from the time shift. The feasibility of these new techniques for correcting spectra with low signal-to-noise ratio, overlapping lines, and broad baseline distortions is demonstrated.