Method for measurement of ion events

1. A mass spectrometer comprising:

an ion source;

an analyser;

an ion detector producing a data stream; and

a processor configured or programmed to:

detect at least one peak in the data stream having an apex with an amplitude above a predetermined threshold; and

extrapolate the segment of the peak which has an amplitude above the predetermined threshold, based on a shaped characteristic of the peak, to estimate the amplitude of the segments of the peak which have an amplitude less than said threshold;

produce a filtered data stream, comprising applying a predetermined threshold to the input data stream, such that the filtered data stream contains only the segment of the peak above the predetermined threshold; and

compile a compensated data stream including the filtered data and extrapolated peak data.

2. A mass spectrometer according to claim 1 , wherein the detecting at least one peak comprises detecting at least one of the leading edge, apex or trailing edge of the peak.

3. A mass spectrometer according to claim 1 , wherein the processor is configured or programmed to produce a filtered data stream, comprising applying a predetermined threshold to the input data stream, such that the filtered data stream contains only the segment of the peak above the predetermined threshold.

4. A mass spectrometer according to claim 1 , wherein if the amplitude of the input data stream at a time T n is less than said threshold, the amplitude in the filtered data stream at time T n is set to one of zero or a constant.

5. A mass spectrometer according to claim 3 , wherein the processor is configured or programmed to:

compile a compensated data stream including the filtered data stream and extrapolated peak data.

6. A mass spectrometer according to claim 1 , wherein the processor is configured or programmed to: sum the estimated amplitude of extrapolated peak data and the filtered data stream over time.

7. A mass spectrometer according to claim 1 , wherein the processor is configured or programmed to estimate a shape characteristic of the peak.

8. A mass spectrometer according to claim 1 , wherein the extrapolating comprises:

detecting the time, T T , at which the amplitude of the trailing edge of the peak in the input data stream falls below the predetermined threshold; and

estimating the amplitude of the peak at time T T by applying a decay function, based on the shape characteristic, to the amplitude of the data peak at time T T−1 , above the predetermined threshold.

9. A mass spectrometer according to claim 8 , wherein the extrapolating further comprises:

estimating the amplitude of the peak at time T n by applying the decay function, based on the shape characteristic of the peak, to the estimated amplitude of the peak at time T n−1 ; and

iteratively applying the decay function for all values of n until the amplitude of the input data stream at time T n is greater than or equal to the predetermined threshold, or the estimated amplitude at time T n is substantially equal to zero, a mean of the baseline, or a constant.

10. A mass spectrometer according to claim 8 , wherein the applying the decay function comprises multiplying the amplitude of the peak at time T n−1 by a constant decay value between 0 and 1.

11. A mass spectrometer according to claim 1 , wherein the extrapolating comprises:

detecting the time, T L , at which the amplitude of the leading edge of the peak in the input data stream increases above the predetermined threshold; and

applying a growth function, based on the shape characteristic, to the amplitude of the data peak at time T L , to produce an estimated amplitude of the peak at time T L−1 .

12. A mass spectrometer according to claim 11 , wherein the extrapolating further comprises:

estimating the amplitude of the peak at time T n−1 by applying a growth function, based on the shape characteristic of the peak, to the estimated amplitude of the peak at time T n ; and

iteratively applying the growth function for all values of n until the amplitude of the input data stream at time T n−1 is greater than or equal to the predetermined threshold; or the estimated amplitude at time T n−1 is less than or substantially equal to zero, a mean of the baseline, or a constant.

13. A mass spectrometer according to claim 11 , wherein the growth function is linear.

14. A mass spectrometer according to claim 11 , in which the amplitude at time T n−1 is estimated by subtracting a predetermined constant from the estimated amplitude at time T n .

15. A mass spectrometer according to claim 11 , wherein the growth function is based on the rate of change of at least part of the segment of the input data stream which is above the predetermined threshold.

16. A mass spectrometer according to claim 1 , wherein if the input data stream includes two or more peaks, and extrapolation of the respective peaks generates conflicting estimates for the amplitude at a time T, the highest of those estimates is selected for time T.

17. A mass spectrometer according to claim 1 , in which the input data stream comprises a signal output from an ion detector, a voltage signal, ion signal, ion current voltage pulse or an electron current pulse, or the output of an analogue to digital converter of an ion detector of a mass spectrometer.

18. A mass spectrometer according to claim 17 , wherein the processor is configured or programmed to apply a smoothing function to the input data stream using a finite impulse response or infinite impulse response filter.