Advantage multichannel

Array detectors make it possible to employ the multichannel advantage and to construct compact instruments without moving parts, useful for process control. 

The large improvement in SNR available with multichannel spectrometers is illustrated in Figure 4.8. Note that the higher SNR was achieved for a shorter measurement time and lower laser power. Although (4.18) states the often quoted Nr multichannel advantage, it should be emphasized that all other experimental parameters were assumed equal. This is rarely the case (and was not in Fig. 4.8), but there is nevertheless a major gain in SNR for multichannel spectrometers. As additional warning deals with multiplex as... 

These multichannel advantages indeed apply under certain conditions, but the situation is rarely so simple. If the power density (Pd) is the same for a point-to-point profile compared to a line image, the point-to-point approach will require N times as long to acquire spectra from N positions along the line. However, the total laser power must be increased to achieve the same Pd for the line focus, by a factor of approximately N. If the same total power (rather than power density) is used for both experiments, the two techniques have comparable total acquisition times for the same SNR. Line imaging would... 

Although the signals predicted in Table 13.1 are indeed small, they are observable experimentally with modem equipment and a low background. The multichannel advantage and low detector noise of CCDs are critical in this regard, as they permit sufficiently long integration times to accumulate... 

Focal plane (array) detectors can detect a range of masses simultaneously. This provides a multichannel advantage that can improve the sensitivity for magnetic sectors, and detection limits can be improved if the analysis is limited by the analyte ion current instead of the chemical background level. This is the case for experiments such as MS/MS, electrospray ionisation, and field desorption. Array detectors can be used with pulsed ionisation methods, but the array detectors for commercial magnetic sector mass spectrometers can only detect a portion of the entire mass range at any given instant. 

Typical performance tests of one of these systems were published in 1985 [28] and 1987 [29]. Comparisons were made with a double 1-m spectrograph in use at the time. Spectra recorded on a triple with a PMT had slightly degraded spectral resolution (relative to a scanning double), but the multichannel advantage implicit in the technique was clearly... 

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