Processing of ion current measurements in time-of-flight mass spectrometers

A method for operating a time-of-flight mass spectrometer comprising an ion source, a pulser, a drift region, a reflector, an ion detector with a secondary electron multiplier, a digitization unit, and a data memory, to form a sum spectrum, comprising the steps:

• pulsing ions into the drift region of the time-of-flight mass spectrometer;
• sampling the electron current which is generated by the ion current in the secondary electron multiplier of the ion detector at the end of the drift region to thereby acquire an individual spectrum;
• in an arithmetic unit that has access to the data memory (i) calculating of total intensity and position on a flight time scale of a ion current peak in the individual spectrum, the latter as a center of gravity of measurement values of the ion current peak in the individual spectrum;
• (ii) selecting two entries in an addition time raster of the sum spectrum, the flight times of which are closest to the position of the ion current peak;
• (iii) determining distances, on the flight time scale, of the flight times of the two selected entries from the position of ion current peak;
• (iv) dividing the total intensity into two portions in proportion of the two distances, and (v) adding the two portions to the two selected entries, with the larger portion being added to the entry which is closer to the position of ion current peak.

A time-of-flight mass spectrometer comprising:

• an ion source;
• an ion guide;
• a pulser;
• a drift region;
• a reflector;
• an ion detector with a secondary electron multiplier;
• a digitization unit;
• and a data memory,
• wherein the pulser is arranged between the ion guide and the drift region and is configured to eject a packet of ions at right angles to the axis of the ion guide into the drift region,
• wherein the digitization unit comprises a module with a plurality of analog-to-digital converters and an arithmetic unit, said analog-digital converters being connected in parallel and configured to sample the electron current generated by the ion current in the ion detector at the end of the drift region to thereby acquire an individual spectrum, and
• wherein the arithmetic unit has access to the data memory and is configured (i) to determine the position of at least one ion current peak on a flight time scale of the individual spectrum as well as the total intensity of the at least one ion current peak, (ii) to select entries in an addition time raster of the sum spectrum, wherein the addition time raster is stored in the data memory and the selected entries are adjacent to the position of the at least one ion current peak, and (iii) to sum portions of the total intensity of the at least one ion current peak to the selected entries, wherein more of the total intensity is summed to selected entries which are closer to the position of the at least one ion current peak than is added to the selected entries which are further away from the position of the at least one ion current peak.