Photographic ion detection

Figure 3.6 Schematicofa double-focusing sector field mass spectrograph with Mattauch-Herzog geometry with a linear imaging curve (double focusing for ions of all masses simultaneously) modified field combination with 70°. In the mass spectrograph, photographic ion detection or focal plane array detectors are used for quasi-simultaneous detection of separated ion beams. (H. Kienitz (ed.), Massen-spektrometrie (1968), Verlag Chemie, Weinheim. Reproduced by permission of Wiley-VCH)...

The pulse repetition rate is normally 100 pulses per sec. with pulse durations of either 10 or 32/u.s. After presparking, spark gap and ion illumination angle control is performed automatically (Conzemius and Svec, 1973b) and the analytical measurements are recorded by either electrical or photographic ion detection techniques. 

To obtain a mass spectrum, ions need to be converted into a usable signal by a detector. The simplest form of ion detection is a photographic plate or a Faraday cup for the direct measurement of the charge. In a Faraday cup the induced current is generated by an ion which hits the surface of a dynode and emits... 

Table 2. Comparison of Photographic and Electro-Optical Ion Detection Methods...

The microchannel plate detector can, however, also work with a metal anode that gathers the stream of secondary electrons at every channel exit. To avoid any confusion, the term array detector is preferably used to describe a microchannel plate where every microchannel remains as an individual ion-detecting element. This array detector acts as electronic photoplates. Indeed, it resembles that of a photographic plate ions with different m/z ratios reach different spots and may be counted at the same time during the analysis. The advantage of array detectors is that analyser scanning is not necessary and therefore sensitivity is improved because simultaneous detection of ions implies that more ions are collected, and this greater efficiency leads to lower limits of detection than for other detectors. 

For ion detection, several approaches are possible. From classical spark source mass spectrometry, the use of photographic plates is known, where very hard... 

For ion detection, several approaches are possible. Classical spark source mass spectrometry has developed the use of photographic plates. Very hard emulsions with low gelatin content are required. Emulsion calibration is similar to that described in optical emission spectrography, but usually varying exposure time are applied instead of using optical step filters. Provided an automated microdensitometer is used, mass spectrography is still a useful tool for survey analysis of solids down to the sub-pg/g level. 

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