Multiple-reaction monitoring transition

The second ones are structural analogues with different masses or even the same mass. In the latter case, chromatographic separation between the analyte and its internal standard must be achieved when distinctive MRM (multiple reaction monitoring) transitions could not be found. It is preferable that the key structure and functionalities (e.g., -COOH, -S02, -NH2, halogens, and heteroatoms) of an internal standard are the same as those of the analyte and differ only by C-H moieties (length and/or position). Modifications in functionalities would result in significant differences in ionization efficiency and extraction recovery [8],... 

MS condition — An API 4000 equipped with a Turbo Ionspray from Applied Biosystems was used as the mass detector and [M + NH4]+ was chosen as the precursor ion for multiple reaction monitoring (MRM) due to the lack of protonated molecular ions. A transition of m/z 434.4 — 273.2 was chosen for paricalcitol and m/z 450.5 —> 379.2 was selected for the structure analog internal standard. 

FIGURE 11.6 Representative multiple reaction monitoring (MRM) chromatogram of whole blood of patient treated with sirolimus (A) m/z 931.5 — 864.6 represents transition of sirolimus at concentration of 10 pg/L eluted at 0.93 min (B) m/z 809.4 — 756.4 represents transition of internal standard ascomycin eluted at 0.89 min. (Source Wallemacq, P.E. et al., Clin Chem Lab Med. 41, 922, 2003. With permission.)... 

Fig. 2.2.9 High-performance liquid chromatography-tandem mass spectrometric analysis of AdoMet and AdoHcy. The analytes were evaluated by multiple reaction monitoring with the following transitions m/z 399 -> 250 for AdoMet m/z 402 -> 250 for the internal standard, tridenterated AdoMet (AdoMet +3) m/z 385 -> 135 for AdoHcy m/z 390 ->- 135 for the internal standard, pentadenterated AdoHcy (AdoHcy+5). Mass spectrometric conditions are described in the text. TIC total ion current, SRM selected reaction monitoring (Figure courtesy of Dr. Ries Duran, Amsterdam)...

Homocarnosine is a dipeptide of GABA and L-histidine. After deproteinizing the sample with ethanol, the mixtures are centrifuged. The clear supernatant is evaporated to dryness and derivatized with butanol. The sample is evaporated to dryness and redissolved in the mobile phase. The homocarnosine-butyl derivatives (Fig. 2.3.4) are quantified using liquid chromatography mass spectrometry/mass spectrometry (LC-MS/MS) operating in the positive mode. With multiple reaction monitoring (MRM), the transitions of m/z 297.0 to m/z 212.0 for homocarnosine and m/z 299.0 to m/z 212.0 for 2H2-L-homocarnosine are quantified. 

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. 

Fig. 4.7.2 Multiple reaction monitoring (MRM) chromatogram of pooled urine spiked with C7-polyols produced by method 1 (without separation of polyol isomers). MRM transitions are given for each mass transition. IS Internal standard...

For the detection, a tandem mass spectrometer Quattro Micro API ESCI (Waters Corp., Milford, MA) with a triple quadrupole was employed. The instrument was operated in electrospray in the positive ionization mode (ESI+) with the following optimized parameters capillary voltage, 0.5 kV source block temperature, 130 °C nebulization and desolvation gas (nitrogen) heated at 400 °C and delivered at 800 L/h, and as cone gas at 50 L/h collision cell pressure, 3 x 1(F6 bar (argon). Data was recorded in the multiple reaction monitoring (MRM) mode by selection of the two most intense precursor-to-product ion transitions for each analyte, except for the ISs, for which only one transition was monitored. The most intense transition for each analyte was used for quantitative purposes. Table 2 shows MRM transitions, cone voltages and collision energies used for the analysis of the antidepressants included in the LC-MS/MS method. 

Multiple Reaction Monitoring (MRM) methods are most commonly used in analytical methods as they provide the opportunity for fast and simple detection and quantification. However, a large number of published methods do not fulfill the international requirement of at least two MRM transitions for reliable identification of an analyte [56-58] which can cause problems particularly... 

Figure 5.4 Chromatograms with multiple reaction monitoring (MRM) transitions at 625/287 (A) and 639/301 (B) that show the multiple glucuronide forms of cyaniding-3-glucoside and peonidin-3-glucoside, respectively. (From Hager, 2008).

A highly specific MS/MS detection, multiple reaction monitoring (MRM), is used to detect C-CTX-1 by mass spectrometry. Three precursor/product transition pairs of (M-I-H-H20) m/z... 

Multiple-reaction monitoring is the most commonly used function for quantification and confirmation. The first quadrupole is set to only filter the selected precursor ion into the collision cell. This ion is then collisionally dissociated to form product ions. A small number of these product ions, which are chosen by the analyst for their structural significance, are then allowed to pass through the third quadrupole to the detector. MRM filters out chemical matrix noise, which results in superior selectivity and great sensitivity. Table 6.1 lists the MRM transitions of... 

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 use of a mass spectrometer as a detector for LC analysis brings a number of benefits to mycotoxin analysis. There is no need for chromophores or fluorophores in the analytes so derivatization can be avoided. The chemical structure of the analytes can be confirmed from molecular mass and fragmentation information and the use of tandem MS (MS/MS) allows greater selectivity. Multiple reaction monitoring and selected ion monitoring modes mean that chromatographic separation of all analytes is not necessary, as differentiation is carried out by the different ion transitions measured, and many multiresidue mycotoxin LC-MS methods now exist. These data acquisition modes can also increase the sensitivity of the method as the background noise is often reduced. 

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