Multiple-reaction monitoring example

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. 

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. 

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. 

Modern triple quadrupole instruments can rapidly switch between many SRM transitions within a single acquisition cycle (MRM), enabling the measurement of multiple analytes simultaneously. It is critical to choose a unique molecular ion and product ion pair (the SRM transition ) for specific monitoring of the targeted analyte. An example of liquid chromatography-multiple reaction monitoring (LC-MRM) analysis of midazolam and its two major metabolites, T-hydroxymidazolam and 4-hydroxy midazolam, is shown in Figure 6.2 [18]. 

MS-MS) techniques. For example, for reliable biomarker data, it is imperative to use multiple reaction monitoring (MRM) or similar techniques that enable separation of different molecular weight hopanes and steranes. 

Electrospray MS. Analysis of methanol solutions in the positive ion mode gives molecular ions of distearyldimethylammonium chloride. Strong ions are seen for the Cj / Cis, Cis/Ci6, and Cifi/Cig homologs, as well as some minor components (15,120). It must be noted that the response factors differ sharply for similar compounds. For example, the response factor for hexadecyltrimethylammonium bromide is only 45% of that for dode-cyltrimethylammonium bromide (117). The same observations on calibration with deuter-ated analogs and fragments for MS-MS analysis made above for FAB also apply to electrospray (117). Electrospray MS was demonstrated for detection of benzalkonium chloride on human skin, using a triple quadrupole instmment in multiple reaction monitoring mode (121). 

By varying the time delay between the pump and probe pulses, information about the time it takes to form the intermediate can be gained. The actual lifetime of the intermediate can then be obtained by continuously monitoring the reactive intermediate over its short lifetime. This leads to decay traces such as that shown in Figure 7.17 A. These traces can be fit to the standard integrated rate laws to extract the appropriate rate constants. Some decay traces have more than one component. Figure 7.17 B, for example, shows a decay trace that indicates both a short and a long component. Hence, fast kinetic techniques can often be used to analyze multiple reactions of reactive intermediates. It may seem that the need to ini-... 

As far as the application of the NIR technique in the polymer field is concerned, a multiplicity of case studies and research papers are reported in the literature ranging from quality control of incoming material to reaction monitoring and extrusion processes. In view of these well-documented applications, only one example will be described here demonstrating the use of on-line NIR spectroscopy in the last stage of the life cycle of a polymer. 

---