Full scan monitoring

Like the UV detector, the mass spectrometer may be employed as either a general detector, when full-scan mass spectra are acquired, or as a specific detector, when selected-ion monitoring (see Section 3.5.2.1) or tandem mass spectrometry (MS-MS) (see Section 3.4.2) are being used. 

To answer this question, we must consider the ways in which the data are acquired. An RIC is generated, post-acquisition, from consecutive full scans in which a small amount of time is spent monitoring each ion, as discussed above. The data produced in a SIM experiment are generated by monitoring only a small number of ions, thus taking advantage of the increased time spent monitoring each ion. 

LC/MS is used as a multi-residue analytical method. The recovery of imidacloprid from tomato was 90-105% for 0.05 and 0.5mgkg . The LOD for imidacloprid was < 10 pg kg in the full-scan mode and 1 pg kg in the selected-ion monitoring (SIM) mode. ... 

The sensitivity depends on the mode of operation. In the full scan mode the sensitivity is limited, while in the selected ion monitoring mode the sensitivity is high. The desired resolution also affects sensitivity (see above). 

Figure 16.1. Screening method for fentanyl analogs in blood using LC-MS/APCI. Monitored ions [M + H]+ were chosen from full scan spectra. The blood sample was spiked with fentanyl, its three analogs and internal standard to the concentration of 5 ng/mL [6].

When operated as a specific detector the ion-trap detector is more sensitive still but not to the extent that would be expected from the performance of other mass spectrometers operated in this mode in view of the large number of ions monitored in full scan mode there is little more sensitivity to be gained by spending a little extra time scanning a narrow mass range, and the detection limit in this mode is in the region of l-2pg. 

The number of ions chosen has an effect on the sensitivity of the analysis. The advantage of SIM is achieved through spending more time monitoring the ions of interest - the more ions being monitored, then the less time will be spent on each of them and the lower the increase in sensitivity of SIM over full scanning. 

Fig. 3.65. Chromatograms monitored in full-scan MS corresponding to solutions of methyl orange degraded at 0, 5, 10, 15, 22 and 27 min each peak is characterized by its mJz value. Reprinted with permission from C. Baiocchi et al. [136],...

Monitoring mode Full scan, SIM Full scan, SIM, product ion scan Full scan, SIM Full range spectrum Full scan, SIM, product ion scan... 

Due to their comparatively low costs and easy operation, quadtupole instruments are the most common instruments used for hyphenation in CEC analyses. However, these instruments only operate at low mass resolution. Sensitivity can be enhanced by operating in selected ion monitoring mode instead of full scanning acquisitions. Unfortunately, this leads to the loss of structural information. The expansion of biological applications has been largely accommodated by the TOE, quadtupole mass filter, and ion-trap instruments. The major advantage of TOE is its potential for speed, resolution, and good mass accuracy. 

Full scan Ql/single ion monitoring (SIM) Ql Scan/fixed Rf mode... 

In this case the survey scan was set as a full scan and the dependent scan as a product ion scan. The problem with data dependent acquisition is to determine the selection criteria. In most cases the system picks up the most abundant ion in the full scan spectrum. An inclusion list with masses of potential metabolites or exclusion list of known interferences significantly improves the procedure. In the example shown in Fig. 1.39, a procedure called dynamic background subtraction (DBS) was applied. This procedure considers chromatographic peak shapes and monitors not the most abundant signal in the spectrum but the largest increase of an ion in a spectrum. The advantage is that once a signal of a peak has... 

The biochemical MS assay performance was studied for various biotin derivatives, such as biotin [m/z 245), N-biotinyl-6-aminocaproic acid hydrazide (m/z 372), biotin-hydrazide (m/z 259), N-biotinyl-L-lysine (m/z 373) and biotin-N-succinimi-dylester m/z 342). These five different bioactive compounds were consecutively injected into the biochemical MS assay. Figure 5.12 shows triplicate injections in the biochemical MS-based system of the different active compounds. Each compound binds to streptavidin, hence the MS responses of peaks of the reporter ligand (fluorescein-biotin, m/z 390) are similar. The use of SIM allows specific components to be selected and monitored, e.g. protonated molecule of the biotin derivatives. In this case, no peaks were observed for biotin-N-succinimidylester (m/z 342), because under the applied conditions fragmentation occurred to m/z 245. In combination with full-scan MS measurements, the molecular mass of active compounds can be determined simultaneously to the biochemical measurement. 

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