BACKFOLDING APPLIED TO DIFFERENTIAL GAS-CHROMATOGRAPHY MASS-SPECTROMETRY AS A MATHEMATICAL ENHANCEMENT OF CHROMATOGRAPHIC RESOLUTION

Differential gas chromatography/mass spectrometry (CC/MS) results in b oth positive and negative differential mass spectra. The method enhanc es the chromatographic resolution and cleans up spectra. Although the method is effective with respect to slowly changing signals, this is n ot true for statistical noise which is aggravated by subtracting spect ra. To remedy this, the two sets of data are combined, after they have been shifted with respect to each other by the width of the chromatog raphic peaks at half-height. This process, called backfolding, has the advantage that a conventional GC trace is produced. By repeating the process of differentiation and subsequent backfolding a number of time s, the chromatographic resolution can be further improved and the mass spectra resemble Library spectra much closer. The method was evaluate d using both simulated and real CC/MS data. The sensitivity of the met hod with respect to applied shift, chromatographic resolution, peak sh ape and concentration was investigated. Backfolding of differential CC /MS does not require sophisticated mathematics. It is easy to implemen t and it is not a burden in terms of CPU time. Application of this met hod allows for a significantly better identification of the components present in the sample to be analysed.