Multiple reactions monitoring

Figure 5.64 LC-UV and LC-MS-MS (multiple-reaction monitoring (MRM)) traces from the analysis of a synthetic mixture of four native and five oxidized deoxynucleosides (for nomenclature, see text). Reprinted by permission of Elsevier Science from Comparison of negative- and positive-ion electrospray tandem mass spectrometry for the liquid chromalography-landem mass speclrometry analysis of oxidized deoxynucleosides , by Hua, Y., Wainhaus, S. B., Yang, Y., Shen, L., Xiong, Y., Xu, X., Zhang, F., Bolton, J. L. and van Breemen, R. B., Journal of the American Society for Mass Spectrometry, Vol. 12, pp. 80-87, Copyrighl 2000 by Ihe American Society for Mass Spectrometry.

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

LC/MS/MS. LC/MS/MS is used for separation and quantitation of the metabolites. Using multiple reaction monitoring (MRM) in the negative ion electrospray ionization (ESI) mode, LC/MS/MS gives superior specificity and sensitivity to conventional liquid chromatography/mass spectrometry (LC/MS) techniques. The improved specificity eliminates interferences typically found in LC/MS or liquid chro-matography/ultraviolet (LC/UV) analyses. Data acquisition is accomplished with a data system that provides complete instmment control of the mass spectrometer. 

Electrospray (Turbo lonSpray), negative ion mode MS/MS with multiple reaction monitoring (MRM) -4500 V... 

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. 

Various analyzers have been used to analyze phenolic compounds. The choice of the MS analyzer is influenced by the main objective of the study. The triple quadrupole (QqQ) has been used to quantify, applying multiple reaction monitoring experiments, whereas the ion trap has been used for both identification and structure elucidation of phenolic compounds. Moreover, time-of-flight (TOF) and Fourier-transform ion cyclotron resonance (FT-ICR) are mainly recommended for studies focused on obtaining accurate mass measurements with errors below 5 ppm and sub-ppm errors, respectively (Werner and others 2008). Nowadays, hybrid equipment also exists, including different ionization sources with different analyzers, for instance electrospray or atmospheric pressure chemical ionization with triple quadrupole and time-of-flight (Waridel and others 2001). 

The LC-MS/MS technique has been used to quantify and identify phenolic compounds. In order to quantify, multiple reaction monitoring (MRM), in which there is a combination of the precursor ion and one of its daughter fragments, is used to characterize a particular compound. This behavior should be as specific as possible in samples with a complex mixture of phenolic compounds. This technique has been largely used to quantify phenolic compound metabolites in urine and plasma (Urpf-Sarda and others 2005, 2007). In this context, LC-ESI-MS/MS with negative mode has been applied for the identification of a variety of phenolic compounds in a cocoa sample (Sanchez-Rabaneda and others 2003 Andres-Lacucva and others 2000). 

FIGURE 1.9 Multiple reaction monitored ion chromatograms for desloratadine (top), 3-hydroxydesloratadine (middle), and phosphatidylcholine monoester (bottom) during post-column infusion and subsequent injection of a SPEC(R) MPl-extracted control blank plasma sample.111 (Reproduced with permission from Elsevier.)... 

The multiple reaction monitoring (MRM) conditions for each analyte were optimized by infusing 0.1 jxglmL of analyte in mobile phase. The Ionspray needle was maintained at 4.0 kV and the turbo gas temperature was 650°C. Nebulizing gas, auxiliary gas, curtain gas, and collision gas flows were set at 35, 35,40, and 4, respectively. In the MRM mode, collision energies of 17,16, and 15 eV... 

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. 

MS condition — An API 3000 equipped with a Turbo Ionspray from Applied Biosystems was used as the mass detector. [M - II was chosen as the precursor ion for multiple reaction monitoring... 

Weaver, R. et al. 2003. Cytochrome P450 inhibition using recombinant proteins and mass spectrom-etry/multiple reaction monitoring technology in a cassette incubation. Drug Metab. Dispos. 31 955. 

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.)... 

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... 

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