In the last few years MALDI has rapidly become a routine tool for the mass analysis of peptides and proteins. It is the nature of the technique that it provides simple to interpret mass spectra with usually only the intact [M+H]+ ion being observed.
Fragment ions of the sample however, can provide valuable structural information. Such fragmentation of peptides can be stimulated by the use of excess laser power during the ionisation process. Separation of the sequence ion fragments is not achieved in linear time-of-flight systems and is difficult in conventional reflectron systems as the ions are not brought into a time focus under the same conditions as the parent ion. Until recently the sequence ion spectrum has only been accessible by a complicated process involving incrementally adjusting the reflectron voltage and collecbng multiple spectra which then all need to be separately calibrated and stitched together in a timeconsuming and laborious manner with little or no guarantee of consistent sensitivity or accuracy of results.
Until now this limitation has prevented the widespread application of peptide sequencing by MALDI as a routine laboratory tool. The instrument described in this paper addresses and uniquely resolves this problem. Using a novel curved field reflectron [1], the sequence ions can be brought into simultaneous time focus without the need for voltage stepping. This seamless data acquisition (SDA) allows an entire sequence spectrum to be acquired extremely quickly in a single scan representing a considerable saving in time and effort.
Calibration is similarly straightforward hence ensuring the accuracy of the results and is performed in seconds. Results are shown from the analysis of a selection of peptide samples. A custom software package prwides full control of all instrument functions. Special tools are provided which aid in the interpretation of the sequence ion spectrum.