Raw NMR spectra of biofluids need several pre-processing steps before multivariate data anlysis can be applied to the set of spectra. The first steps are typical NMR pre-processing steps routinely applied to all NMR spectra. These steps include the Fourier transformation of the free induction decay (FID), a phasing of spectra and finally a baseline correction of spectra. These steps are all included in pre-processing of typical NMR spectra, whereby the water background of biofluids often pushes these procedures to the limits. Two pre-processing methods, which are rather specific for metabonomic measurements, are the binning of spectra and the normalization of spectra. In addtion, specific regions of the spectra, which contain non-reproducible peaks, are often excluded from further analyses.These three methods are explained in more detail in this section.
NMR spectrum before and after pre-processing steps (region exclusion and binning), which are typical for analyses of spectra from metabonomic studies.