Processing baseline correction

Some extensions are not essential for CC, but greatly improve its capabilities. Interfaces to a data storage device and to a hard copy unit are valuable. Some facility for data processing afterwards (baseline correction and peak area determination) is desirable. 

Hippe et al. discussed numerical operations for computer processing of (gas) chromatographic data. Apart from a baseline correction method, a method of reco -tion of peaks is described. The relationship between the convexity of an isolated peak and the monotonic nature of its first derivative is used to find the most probable deflection points. The munber of maxima and shoulders are used for a decision if the segment of the chromatogram contains an isolated peak or an unresolved peak complex. The number of shouders and maxima determine the total number of component peaks. 

There are three main processing options based on the addition of a processing or correction function to the FID DC- or Baseline-Correction, Zero-Filling and Linear Prediction LP. 

With ID WIN-NMR the compensation of DC offsets is the only baseline correction option for ID FIDs. It is automatically performed prior to any processing when confirmed in the dialog box that appears on screen. The baseline of the FID is corrected with the zero-line set to the mean value of the last part of the FID. 

With 2D WIN-NMR baseline corrections are automatically applied for FIDs in t2 and tl prior to any processing when the Fourier transformation is initialized with the xfl, xfl, xfb or xtrf commands. According to the parameter BC mod set for F2 and Fl separately, either a simple DC correction or more sophisticated algorithms are applied to correct the FID baselines in F2 and Fl (Table 5.2), thereby taking into account the detection mode (single/quadrature). 

Try out the effect of several modes for DC correction available with 2D data. Load the raw data of the magnitude mode 2D COSY spectrum D NMRDATA GLUCOSE 2D HH GHHCO 001001.SER and choose no, quad and qpol as BC mod in F2. Note that usually for Fl no baseline correction is applied in the time-domain, i.e. BC mod (F1) = no. Fourier transform the data and store the individual spectra using ascending processing numbers. Compare corresponding rows to inspect the effect of different baseline corrections. 

After processing in the time domain, Fourier transformation, phasing and basic processing (calibration, peak picking, integration) ahs been performed, additional processing steps to improve spectral quality are at your disposal. This includes operations common to both ID and 2D spectra e.g. baseline correction in the frequency domain, as well as operations specific to these different type.s of data sets. 

In this section, we present the development of an automated protocol for prostate tissue histology [164] from infrared spectroscopic imaging data as an example of the techniques described (Fig. 8.11). The data is three dimensional with x-y—axes representing the image plane and the 2-axis representing the spectral dimension. After data acquisition, two important pre-processing steps, namely baseline correction and de-noising, are performed. Since the entire data set is derived from human tissue samples, the spectra have similar characteristics and, therefore, a manually chosen set of pre-defined wave number could be used as the reference points for baseline correction. It is... 

The data processing can be divided into three phases. Phase 1 is the removal of poor quality spectra with an automated routine. Phase 2 is the data preprocessing of the spectra, which passed the quality test. This usually entails some type of baseline correction and normalization process. Phase 3 is multivariate image reconstruction where the spectra are classified and reproduced as color points... 

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