1289230 Calculating ASSOCIATED ELECTRICAL INDUSTRIES Ltd 28 May 1971 [9 June 1970] 27920/70 Heading G4A A computer, supplied with input data containing information as to the magnitudes and positions of peaks in a measured mass spectrum, is programmed to identify peaks corresponding to three given mass/charge ratios by (i) identifying two of the peaks in the measured spectrum as those with the highest and lowest mass/charge ratio of the given three ratios on the basis of an initial assumption concerning the relative proportions of substances in the measured sample, (ii) calculating by interpolation the position of the peak corresponding to the intermediate one of the three ratios, (iii) attempting to identify the intermediate peak in the measured spectrum from its calculated spectrum and (iv) in the event of failure of (iii) to modify the initial assumption and repeat the process until successful identification of the intermediate peak is achieved or until a predetermined condition has been reached. The output of a mass spectrometer output may be digitized and entered into a disc or tape unit of the computer from which it is subsequently retrieved for analysis. The time centroid #V n t n /#V n and intensity #V n for each peak in a reference spectrum are calculated from successive amplitude samples of the peak. The eight peaks of highest intensity are identified and arranged in ascending mass/charge ratio order, the first P 1 being assumed to be the lowest of the three given peaks and the peak with highest intensity starting six peaks higher up in the spectrum being assumed to be the highest P 3 of the three given peaks. The intermediate peak position is calculated by exponential interpolation. If a peak is found in the measured spectrum within a predetermined range of the calculated position, its identification is conditional on its intensity being between 10 and 40% of that of P 1 . If P 2 is not successfully identified, the next peak of the list of eight is selected as P 2 and the process is repeated, the computer being stopped and the operator notified if successful identification is not achieved having tried all eight peaks. With P 1 , P 2 and P 3 successfully identified, the other peaks in the reference spectrum are identified by exponential extrapolation and/or interpolation and comparison with the measured peaks to construct an internal calibration table in the computer core memory. Using this table, unknown spectra stored in the computer can be identified, the time scale of each spectrum being shifted so that one of its peaks coincides with the corresponding peak in the reference spectrum, the charge/mass ratios of the peaks being calculated by interpolation and the results printed out or recorded by a digital plotter.