Method of mass analysis and mass spectrometer
Mass analysis method and mass spectrometer in which the S/N of mass spectra does not deteriorate due to accumulation if an ionization method, such as MALDI, producing spectral intensities that are not uniform in time is employed. Every given number of collected mass spectra are accumulated and stored to produce primary accumulation mass spectra. After the measurements, some of the stored primary accumulation spectra are selected according to a given rule based on a time trace of the intensities of the primary accumulation mass spectra. The selected spectra are accumulated to produce a secondary accumulation mass spectrum.
1. A method of mass analysis for finding an accumulation mass spectrum by performing multiple mass measurements using a mass spectrometer, collecting mass spectra from the measurements, and accumulating the collected mass spectra, said method of mass analysis comprising the steps of:
(a) accumulating every given number of the collected mass spectra and storing resulting spectra as primary accumulation spectra;
(b) selecting primary accumulation spectra from the stored primary accumulation spectra according to a given rule after the end of the measurements; and
(c) accumulating the selected primary accumulation spectra to obtain a secondary accumulation spectrum.
2. A method of mass analysis as set forth in claim 1 , wherein said mass spectra are obtained by MALDI (matrix-assisted laser desorption/ionization).
3. A method of mass analysis as set forth in claim 1 or 2 , wherein said mass spectrometer is a time-of-flight mass spectrometer.
4. A method of mass analysis as set forth in claim 1 or 2 , wherein said rule is to select one time interval or plural discrete time intervals from a period in which mass spectra are collected such that the primary accumulation spectra in the selected time intervals have good S/N.
5. A method of mass analysis as set forth in claim 1 or 2 , wherein said given rule consists of setting a minimum threshold value for spectral intensities and selecting primary accumulation spectra having intensities exceeding the minimum threshold value.
6. A method of mass analysis as set forth in claim 5 , wherein said given rule consists of further setting a maximum threshold value and excluding primary accumulation spectra having intensities exceeding the maximum threshold value.
7. A method of mass analysis as set forth in claim 1 or 2 , wherein said given rule consists of (i) selecting one time interval or plural discrete time intervals in which the primary accumulation spectra have high S/N, (ii) simultaneously setting a minimum threshold value for intensities of the primary accumulation spectra, and (iii) selecting the primary accumulation spectra having intensities exceeding the minimum threshold value.
8. A method of mass analysis as set forth in claim 7 , wherein said given rule consists of further setting a maximum threshold value and excluding the primary accumulation spectra having intensities exceeding the maximum threshold value.
9. A method of mass analysis as set forth in claim 1 , wherein said given rule is carried out based on a time trace of intensities of the primary accumulation spectra.
10. A method of mass analysis as set forth in claim 1 , wherein said spectral intensities are intensities of given peaks of the collected mass spectra.
11. A method of mass analysis as set forth in claim 1 , wherein said spectral intensities are intensities of all signals within all ranges of collected mass spectra or within a given range of mass-to-charge ratios.
12. A method of mass analysis as set forth in claim 1 , wherein said given rule consists of selecting primary accumulation spectra in turn out of the collected primary accumulation spectra from a primary accumulation spectrum having highest S/N and accumulating the selected primary accumulation spectra such that S/N of said secondary accumulation spectrum is improved best.
13. A method of mass analysis as set forth in claim 12 , wherein said given rule is to terminate accumulation for obtaining said secondary accumulation spectrum when S/N of the secondary accumulation spectrum has ceased to be improved.
14. A method of mass analysis as set forth in claim 1 , wherein the mass spectrometer is compensated for drift during the step (a) for obtaining the primary accumulation spectra.
15. A mass spectrometer having a function of obtaining an accumulated mass spectrum by performing multiple mass measurements, collecting mass spectra from the measurements, and accumulating the mass spectra, wherein every given number of the collected mass spectra are accumulated and stored to produce accumulation mass spectra, and wherein a time trace of intensities of the accumulation mass spectra is displayed on a display device.
16. A mass spectrometer as set forth in claim 15 , wherein said intensities of the accumulation mass spectra are intensities of given peaks of the collected mass spectra.
17. A mass spectrometer as set forth in claim 15 , wherein said intensities of the accumulation mass spectra are intensities of all signals within all ranges of collected mass spectra or within a given range of mass-to-charge ratios.