It is known to record or digitise individual signals or transients arising from ion arrivals at an ion detector or an electron multiplier using an Analogue to Digital recorder or an Analogue to Digital Converter (“ADC”). Orthogonal acceleration Time of Flight mass spectrometers may digitise ion arrival signals or transients relating to many thousands of individual time of flight separations. The digitised signals or transients are summed to produce a final summed or composite time of flight mass spectrum. Each individual time of flight spectrum, signal or transient may be processed in real time before summing. In the simplest case this processing may be the application of an amplitude threshold to isolate signals arising from ion arrivals from background noise or baseline noise. The signal at individual digitised samples (i.e. individual Analogue to Digital Converter time bins) or within a time of flight spectrum which is above the threshold may be recorded and all other samples or intensity values in Analogue to Digital Converter time bins may be set to zero or to a baseline value. Multiple time of flight spectra processed in this way may then be summed or averaged to generate a final summed spectrum with reduced noise.
It is also known to process individual signals or transients which have been digitised to reduce the ion arrival signals or transients into time and intensity pairs. Such a method is disclosed, for example, in U.S. Pat. No. 8,063,358 (Micromass). Individual signals or transients which are reduced to time and intensity pairs may then be summed with other time and intensity pairs relating to other time of flight spectra, signals or transients in order to produce a final summed, composite or average spectrum. This method advantageously substantially removes the profile or line width of the digitised signal from the final summed spectra thereby increasing the effective time of flight resolution.
However, one particular problem with conventional Analogue to Digital Converter detection systems is that they can still suffer from a relatively limited dynamic range.
Arrangements are known which comprise dual Analogue to Digital Converters in an attempt to extend the dynamic range as is disclosed, for example, in U.S. Pat. No. 8,354,634 (Micromass).
It is desired to provide an improved method of mass and/or ion mobility spectrometry.