Scanning multiple-reaction monitoring

Several MS acquisition and data processing strategies are used for detection and structure elucidation of metabolites. The common metabolite detection strategies are summarized in Section 9.2.1, which include full MS scan, constant neutral loss, parent ion scan, multiple reactions monitoring, and mass defect filtering. The structure elucidation strategies feature product ion scan, multistage scan, and accurate mass measurement, which are reviewed in Section 9.2.2. 

Skutlarek D, Faerber H, lippert F, Ulbrich A, Wawrzun A, Buening-Pfaue H (2004) Determination of glucosinolate profiles in Chinese vegetables by precursor ion scan and multiple reaction monitoring scan mode (LC-MS/MS). Eur Food Res Technol 219 643-649... 

Formiminoglutamate (FIGLU), a marker for glutamate formimino-transferase deficiency, was recently also shown to be detectable by acylcarnitine analysis represented as a peak with m/z 287 (Fig. 3.2.3d) [64]. In poorly resolved acylcarnitine profiles, this peak may be confused with iso-/butyrylcarnitine (m/z 288). To avoid the incorrect interpretation of acylcarnitine profiles, we recommend performing the analysis in product scan mode as opposed to multiple reaction monitoring (MRM) mode. For example, the FIGLU peak at m/z 287 would not have been correctly identified in MRM mode because the transition of 287 to 85 is typically not selected. However, the 288/85 transition would reveal abnormal results, but in fact not represent either butyryl- or isobutyrylcarnitine, but another FIGLU related ion species. 

Several scan modes are unique to the triple-quadrupole instrument, and most of these modes are superior in duty cycle versus an ion trap, Fourier transform (FT), or time-of-flight (TOF) mass spectrometers. Different elements of the triple-quadrupole perform different operations for each scan mode. These scan modes, each of which will be described in detail, are single-reaction monitoring (SRM) or multiple-reaction monitoring (MRM), precursor ion scanning (PIS), and constant-neutral-loss scanning (NLS). These scan modes and applications for structural elucidation have been described in detail (Yost and Enke, 1978, 1979). 

QqQ MS) are, on the other hand, a good option for sensitive, quantitative targeted analysis using multiple reaction monitoring (MRM), and they can also be used for class-specific detection through precursor ion and neutral loss scanning (4-6). 

For abbreviation of analyte names see Sect. Abbreviations . ACN acetonitrile, APCI atmospheric pressure chemical ionization, dial, microdialysis samples, ESI electrospray ionization, FA formic acid, iso isocratic, IT ion trap, lin range linear range, MeOH methanol, MRM multiple reaction monitoring, MS full scan mass spectrometry, n.s. not specified, OAc acetate, QqQ triple quadrupole mass spectrometer, SIM selected ion monitoring, Solv HPLC solvent, SQ single quadrupole mass spectrometer, T temperature Ratios given as v/v... 

Fig. 5 Statistical evaluation of LC-MS-based methods for tropane alkaloids referred in this chapter. (a) Relative frequency of ionization methods. +APCI positive atmospheric pressure chemical ionization, +ESI positive electrospray ionization, FAB fast atom bombardment, +TSP positive thermospray, (b) Relative frequency of scan modes used. MS full scan MS, MS/MS tandem mass spectrometry (product ion scan), MRM multiple reaction monitoring, SIM selected ion monitoring, (c) Relative frequency of mass analysers used. EBQtQ2 double focusing sector field mass spectrometer, IT ion trap, QqQ triple quadrupole, SQ single quadrupole. Considered publications were found by PubMed data-based search and references cited in these articles...

For trace analysis, in which full-scan data cannot be obtained and selected ion monitoring (SIM) or multiple reaction monitoring (MRM) is required, no criteria have been established by the OPCW. Rodriguez and Orescan (23) proposed the following criteria for confirmation of trace levels of pesticides by LC/API/MS under MS conditions that promoted in-source CID ... 

Two approaches are often used to improve the detection limit, including selected ion monitoring (SIM) and multiple reaction monitoring (MRM). In LC/MS studies, it is often desirable to increase detection sensitivity by hmit-ing the mass analyzer scan to just one ion— that is, SIM. In this mode, a single ion of interest is monitored continuously by a mass spectrometer and no other ions are detected. This results in signihcant improvement of signal-to-noise ratio. SIM trades specihcity for sensitivity. In general, the sensitivity in SIM is increased by a factor of 100 to 1000 over full-scan mass spectra. This can be quite useful in detection and quantihcation of specihc compounds at low levels. 

For example, some parameters are the same in both applications and present no problem in the data migration project. An example of this parameter is the scan type such as Multiple Reaction Monitoring (MEM) that is present in both applications. Therefore, the migration is relatively straightforward and the acceptance criteria that are set are an exact match. 

Depending on the objectives of the analysis, the mass spectrometer will be operated in various modes of data acquisition such as MS, tandem MS or MS/MS, selected ion monitoring (SIM), multiple reaction monitoring (MRM), fiill-scan or limited mass range, data dependent, and so forth. SIM/MRM conditions will improve the detection limits, while data-dependent MS/MS acquisitions will worsen them. The data acquisition/storage speed and the number of averaged spectrum are all factors that will ultimately affect the detection limits. 

Figure 2.2 Scan types utilized in lipidomic analysis by ESl-MS/MS. An MS/MS instrument consists of an initial mass (m/z) analyzer (MSi), a collision cell, and a second mass (m/z) analyzer (MSj). The two mass (m/z) analyzers and collision cell are separated in space on a beam instrument, such as tandem quadrupoles and Q-TOFs, and in time in ion traps. Product-ion, precursor-ion, and neutral-loss scans are performed by respectively scanning MSj, MSj, or MSj and MS2 in parallel. Multiple reaction monitoring (MRM) chromatograms are recorded with MSj and MSj fixed for transitions of interest. MS or MS/MS/MS spectra are recorded when a third mass (m/z) analyzer MS3 is utilized following a second collision cell. MS and further MS" spectra are often recorded on ion-trap instruments.

The fourth scan, selected-reaction monitoring (SRM), is useful in quantitative measurements of analytes present in complex mixtures (see Chapter 14). Conceptually, this scan mode is similar to the product-ion scan. However, instead of scanning the second mass spectrometer in a broad mass range, the two mass analyzers are adjusted to monitor one or more chosen precursor-product pairs of the analyte. This operation is identical to the selected-ion monitoring mode (SIM see Chapter 14) of data acquisition. Monitoring more than one reaction is termed multiple-reaction monitoring (MRM). 

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