Multiple reactions quantitative analysis

So far, as in Equation (3.33), the hydrolyses of ATP and other high-energy phosphates have been portrayed as simple processes. The situation in a real biological system is far more complex, owing to the operation of several ionic equilibria. First, ATP, ADP, and the other species in Table 3.3 can exist in several different ionization states that must be accounted for in any quantitative analysis. Second, phosphate compounds bind a variety of divalent and monovalent cations with substantial affinity, and the various metal complexes must also be considered in such analyses. Consideration of these special cases makes the quantitative analysis far more realistic. The importance of these multiple equilibria in group transfer reactions is illustrated for the hydrolysis of ATP, but the principles and methods presented are general and can be applied to any similar hydrolysis reaction. 

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]... 

Wolf-Yadlin, A., Hautaniemi, S., Lauffen-burger, D.A. and White, E.M. (2007) Multiple Reaction Monitoring for Robust Quantitative Proteomic Analysis of Cellular Signaling Networks. Proc Natl Acad Sci, 104, 5860-5865. 

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 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. 

For purposes of quantitative analysis, selected ion monitoring (SIM) and selected reaction monitoring (SRM) are two commonly utilized approaches. The latter is also referred to as multiple reaction monitoring (MRM). In both modes, considerable structural information is lost nonetheless, these techniques are extremely powerful for target compound quantihcation in biological matrices, if the compound of interest is known. 

Wolf-YadUn A, Hautaniemi S, Lauffenburger DA, White FM. Multiple reaction monitoring for robust quantitative proteomic analysis of cellular signaling networks. Proc Natl Acad Sci U. S. A. 2007 104 5860-5865. 

Multiple sprayers from several liquid streams were used to study gas-phase ion-ion and ion-molecule reactions in the ESI source. A seven-channel ESI device was applied to study gas-phase reactions of proteins [59], but also to facilitate the protonation of highly reactive pyrolytically-produced ketenes [60]. The analyte is fed through the centre capillary, while a reagent solution is introduced through the outer six channels A dual-sprayer device was used to study the mechanism of matrix-related ion-suppression effects in quantitative analysis (Ch. 11.5.1, [61]). 

Multiple reaction monitoring (MRM) Selective mass filter Selective mass filter Yes Quantitative analysis Selective detection of target ions. Optimum ion detection mode. No mass spectrum obtained. Triple-quadrupole only... 

For a comprehensive assessment of electrocatalytic specificity, a quantitative determination of the rate and the kinetics of each possible path is necessary under various conditions. We recently discussed a phenomenological analysis of multiple reactions in parallel or in series to obtain electrode kinetic information and criteria for selectivity control (60, 61. Previous... 

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