Digital Electronics for Ion Counting Detectors

The most accurate and precise quantitative measurements do not employ the current measurement methods described thus far, but instead use ion counting techniques. The use of ion counting techniques in mass spectrometric analyses of very small samples was first intoduced (Barton 1960 Ihle 1971) for determination of relative isotope abundances in radioactive metals, but the first published report of application to trace level quantitation of organic analytes by GC/MS appears to have been somewhat later (Picart 1980) modem practice uses the same fundamental principles but with greatly improved detector and electronics technology. 

CEMA dead times, typically lns (i.e. of the same order as the width of a TOFMS mass peak but usually less than the spacing between mass peaks 1 Th apart), provide a limit to the upper end of the dynamic range for any ion counting strategy. However, since ion arrival times are described by Poisson statistics (see the text box in this 

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