Selected individual mass recording

In the use of conventional mass spectrometers (beam instruments), the detection limit in the full scan mode is insufficient for trace analysis because the analyser only has a very short dwell time per ion available during the scan. Additional sensitivity is achieved by sharing the same dwell time between a few selected ions only by means of individual mass recording (SIM, MID) (Table 2.53 and Figure 2.221). 

Selected ion monitoring, recording of individual pre-selected ion masses, as opposed to full scan, -> also MID. 

Mass spectra recorded using LC/MS software may be displayed individually, signal averaged, and background subtracted. Furthermore, these data may be used to plot computer-reconstructed selected ion or total ion chromatograms. 

Data curves together with all associated parameters are stored on mass storage media. At retrieval, the stored curves and the related parameter are loaded and can be modified. After retrieval, (I) data can be plotted as multiple kinetic curves, and each individual curve, can be the average of several stored experiments, (2) spectra can be constructed at selected times from a file of kinetic curves recorded at various wavelengths, (3) computer simulation can be carried out and compared immediately with the kinetic data, as discussed below. 

The physical property measured and the corresponding thermal analysis technique are tabulated in Table 1.1 (3) and further elaborated on in Chapter 13. Notice that under the physical property of mass, thermogravimetry (TG), evolved gas detection (EGD), evolved gas analysis (EGA), emanation thermal analysis (ETA), thermoparticulate analysis, and others are included. Similar considerations can be included in the physical proparties of optical characteristics, electrical characteristics, magnetic characteristics, and so on. The definitions of each individual technique are given in the chapter in which they are discussed. A select number of the thermal analysis techniques are summarized in Table 1.2. Each technique is tabulated in terms of the parameter measured, a typical recorded data curve, the instrumentation needed, and the chapter in which it is described. 

Among these three conditions, only the first approach or its variations was used widely in practice. Accordingly, a total ion current chromatogram of each individual molecular ion can be extracted (i.e., selected-ion monitoring) from the recorded mass spectra in the full MS mode from an HPLC run. Indeed, many ions of interest can be extracted simultaneously in this way [51]. To perform quantitative analysis of lipids, the linear dynamic range, limit of detection, and calibration curves of the molecular species of interest are generally predetermined. Thus, the reconstituted ion peak area of each species can be compared to a standard curve obtained under identical experimental conditions. 

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