Time-of-flight effects in matrix-assisted laser desorption/ionization fourier transform mass spectrometry

✍ Scribed by T.-P. E. Sze; T.-W. Dominic Chan

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 137 KB
• Volume: 13
• Category: Article
• ISSN: 0951-4198
• DOI: 10.1002/(sici)1097-0231(19990315)13:5<398::aid-rcm499>3.0.co;2-d

✦ Synopsis

The time-of-flight effect in Fourier transform mass spectrometry (FTMS) with an external ion source was quantified. The time-of-flight profiles of ions of different masses were measured by stepping the time interval between the ionization pulse and the gating of the trapping voltage (T gate ). The optimal gate times for trapping ions of different masses were found to correlate with the mass-to-charge ratios of the ions using a typical time-of-flight equation (i.e. t G p (m/z)). The time-of-flight effect narrowed the effective mass range of matrix-assisted laser desorption/ionization (MALDI)-FTMS hence limiting the applicability of the technique for mixture analysis. To overcome this time separation effect, T gate was incremented while summing individual MALDI-FT mass spectra. Early attempts at using this 'scanning' FTMS method experienced substantial signal cancellation during spectral summation. This signal cancellation was subsequently attributed to the T gate -dependent alternation of the phase angle of the MALDI-FTMS signals. By incorporating suitable compensation delays in the pulse program, we succeeded in preserving the phase coherency of the FTMS signals at different values of T gate , and managed to obtain a MALDI mass spectrum of a mixture of 3-aminoquinoline (3-AQ), luteinizing hormone releasing hormone (LHRH) and gramicidin-D (m/z range from $150 to 2000).