Fitting of the beat pattern observed in NMR free-induction decay signals of concentrated carbohydrate-water solutions

A series of mathematical functions has been used to fit the proton free-induction decays (FIDs) of concentrated carbohydrate-water samples. For the solid protons, these functions included a sine function, as well as the Fourier transforms of single and multiple Pake functions multiplied by a Gaussian broadening. The NMR signal from the mobile protons is described by an exponential function. It is found that in most cases the sine function gives a satisfactory result and provides valuable information about the second moment M-2 and the ratio of solid to mobile protons (f(s)/f(m)). A good indication for using the sine function is the presence of a beat in the FID. For high temperatures this approach breaks down, and a biexponential fit is more appropriate. If a clear dipolar splitting is observable in the NMR spectra, the Pake function (or a multiple Pake fit) should be used. In this case information about M-2 and f(s)/f(m) can also be obtained. (C) 2004 Elsevier Inc. All rights reserved.