Data processing technique in gas chromatography/time-of-flight mass spectrometry.

A complete mass spectrum was measured at an acquisition rate of 1 kHz using a femtosecond-multiphoton-ionization time-of-flight mass spectrometer for analyte eluting from a gas chromatograph. A contour-map display, i.e. a two-dimensional plot, of the data was first constructed for a simultaneous overview of the mass spectra and the mass chromatograms. The noise component in the signal was then reduced by digital filtering and reduced further by smoothing the data. The detection limit (S/N = 3) was improved from 240 to 76 fg for 2,3,4,6,7-pentachlorodibenzofuran, with no appreciable loss of resolution in the chromatogram. The achieved value was lower than the value (<100 fg) required by Japanese Industrial Standards for dioxin analysis. A new parameter, referred to as a 'reliability factor', was defined in this study to calculate the similarity between the intensity distribution of the isotope peaks observed in the mass spectrum and that calculated from the natural abundance ratio of the isotopes. This parameter was useful for evaluation of the purity of the chromatographic peak.