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By by Birendra N. Pramanik (Editor), A.K. Ganguly (Editor), Michael L. Gross (Editor)

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Quantitative analysis is also adversely affected by limited detector dynamic range. One approach to dealing with the limitations of a single TDC-based detector with a single time-to-digital converter is to use multiple detectors with multiple time-to-digital converters (438). This requires that the ion beam be defocused so that as ion current increases, individual ions have a higher probability of striking physically different detectors. This reduces the likelihood of two or more ions striking the detector during the TDC recovery period.

An alternative approach has been proposed by Cody (286c). Instead of measuring n samples one at a time, one can measure n/2 samples simultaneously in n linearly independent combinations. This provides a set of n equations in n unknowns, and the mass spectrum for each analyte can be obtained by using Hadamard transform techniques. This provides a signal-to-noise (S/N) improvement that increases with n: S/N ϭ 1n 2 (3) For large n, it reduces the time required to achieve a given signal-to-noise ratio to 4/n.

Scanning array detectors such as position- and timeresolved ion counting (PATRIC) detectors (349) and charge-coupled device (CCD) array detectors (350) have been used with good success for ESI-MS experiments with magnetic sector mass spectrometers. Tandem mass spectrometry capabilities are possible with linked-scanning methods, which also provide kilovolt collision energies for high energy CID experiments that tend to be information-rich and relatively insensitive to variations in experimental conditions (Fig.

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