Tandem mass spectrometry with feedback control
View Patent ↗The invention relates to acquisition methods for fragment ion spectra of biopolymer molecules in tandem mass spectrometers which are coupled to separation devices. The invention provides a real-time method for calculating a quality coefficient for each fragment ion spectrum. The quality coefficient indicates whether the fragment ion spectrum can be used successfully for identifying the biopolymer molecule or whether it should be acquired once more, possibly with other acquisition parameters.
1. Method for the acquisition of a fragment ion spectrum of biopolymer ions in a tandem mass spectrometer, comprising the following steps:
a) acquiring a first fragment ion spectrum of a biopolymer ion using a fragmentation method with first fragmentation method parameters,
b) calculating a quality coefficient in real time from the first fragmention ion spectrum data, wherein the quality coefficient corresponds to a length of a chain of polymer building blocks inferred from signals of the first fragment ion spectrum data,
c) deciding from the value of the quality coefficient, whether a further fragment ion spectrum of this biopolymer ion is to be acquired, and
d) in case of a positive decision, immediately reacquiring a second fragment ion spectrum of a biopolymerion of a same type as that used in step (a) using the same fragmentation method used in step (a) with second fragmentation method parameters that differ from the first fragmentation method parameters.
2. Method according to claim 1 , wherein the tandem mass spectrometer measures samples of biopolymers which have been separated by a separation method such as liquid chromatography or capillary electrophoresis.
3. Method according to claim 2 , wherein the tandem mass spectrometer is directly coupled to the separation method.
4. Method according to claim 1 , wherein the biopolymer ions are digest peptide ions.
5. Method according to claim 1 , wherein the calculation of the quality coefficient comprises the steps:
calculation of the mass values of the fragmentions in the fragment spectrum, and
examining the mass differences of these mass values for coincidences with masses of biopolymer building blocks, of biopolymer building block modifications, or of short chains of biopolymer building blocks.
6. Method according to claim 5 , wherein the mass differences can be checked for coincidences by means of a check mass table, having positive entries for all possible mass values for single polymer building blocks, polymer building block modifications, or short chain of polymer building blocks with and without possible modifications.
7. Method according to claim 6 , wherein the graduation of the mass values in the check mass table is as fine as the measuring accuracy of the mass spectrometer allows.
8. Method according to claim 6 , wherein the sum of the entries in the check table gives the quality coefficient for the longest closed chain.