Selected/multiple reaction monitoring

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. 

When using MS/MS and more selective multiple reaction monitoring detection, it is recommended that the formation of sodimn adducts is suppresses, as these fragment poorly. ESI-MS/MS permits unambiguous identification and structure elucidation vmder negative ionization conditions of acidic alkyl-phenolic compounds (i.e., APECs) and fully de-ethoxylated alkylphenols. An example of MS/MS spectra of NP and NPjEC is shown in Figure 3. 

Selected/Multiple Reaction Monitoring for LC-MS Selected/multiple reaction monitoring (SRM/MRM), which is the special case of either PIS or NLS (see Chapter 2), becomes the preferred method for detection of a particular ion since it can be done in a very short time frame. SRM/MRM could be very specific if the monitored fragment ion is specific to the precursor in combination with an LC separation and no interfering transitions are concomitantly present. 

Once the analyte has been identified and characterized, it is possible to determine its quantity. This is important information in a lot of fields and in cultural heritage in particular. There are specific experimental set-ups for quantitative analysis, such as selected ion monitoring (SIM) and multiple reaction monitoring (MRM). By considering that MS is highly sensitive, it is possible to carry out quantitative determinations of compounds at trace level.[7,8]... 

SIM, selected ion monitoring SRM, selected reaction monitoring MRM, multiple reaction monitoring. 

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. 

Multiple Reaction Monitoring (MRM) See selected reaction monitoring. 

Selected Reaction Monitoring (SRM) Data acquired from specific product ions corresponding to m/z selected precursor ions recorded via two or more stages of mass spectrometry. Selected reaction monitoring can be preformed as tandem mass spectrometry in time or tandem mass spectrometry in space. The term multiple reaction monitoring is deprecated [1],... 

Multiple reaction monitoring (MRM)a Detection of selected mass transfers quantitation Low High... 

GC/MS(/MS) is also popular for quantifying DBFs. Selected ion monitoring (SIM) or multiple reaction monitoring (MRM) mode are used with GC/MS and GC/ MS/MS, respectively, to maximize the sensitivity and provide low detection limits. Some EFA Methods utilize GC/MS, including EFA Method 524.2, which uses GC/ EI-MS for THM analysis [155], and EFA Method 521, which uses for GC/CI-MS/ MS for nitrosamine analysis [55]. In addition, many priority unregulated DBFs have been measured using GC/MS in a U.S. Nationwide Occurrence Study [11,12]. 

Following extractive deproteinization of the plasma, the amino acids (and their stable-isotope-labeled internal standards) are separated by HPLC and introduced into the mass spectrometer. Electrospray ionization results in the formation of electrically charged molecules, which are separated on the basis of their mass/charge (m/z) ratio in the first quadrupole. Following fragmentation in the collision cell, the characteristic fragment for each amino acid is selected in the second quadrupole. This process is named multiple reaction monitoring. 

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)...

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. 

Lopshire [188] explored the exchange reaction of chlorine by oxygen with polychlorobiphenyl anions as a method of compound-selective polychloro-biphenyl congener detection in a gas chromatography-mass spectrometric system. Multiple reaction monitoring allowed separate chromatograms to be detected for each different polychlorobiphenyl composition from tetra-through nonachloro. 

DE, two-dimensional gel electrophoresis WB, Western blot MS, mass spectrometry LC, liquid chromatography 2DE DICE, two-dimensional difference gel electrophoresis, SRM, selected-reaction monitoring MRM, multiple reaction monitoring AQUA, absolute protein quantitation SMIM, selected MS/MS ion monitoring. ... 

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. 

Gschwend MH, Arnold P, Ring J, Martin W (2006) Selective and sensitive determination of amisulpride in human plasma by liquid chromatography-tandem mass spectrometry with positive electrospray ionisation and multiple reaction monitoring. J Chromatogr B Analyt Technol Biomed Life Sci 831(1-2) 132-139. doi S1570-0232(05)00890-l [pii] 10.1016/j.jchromb.2005.11.042... 

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