Multiple-ion monitoring

Multiple-ion monitoring is, however, of considerable value in structural studies, but only if model compounds of known structure are available for comparison. Such an approach has been used in the study of the carbohydrate structures of glycoproteins from different tissues.50 Separation of glycopeptides obtained from various tissues was performed on columns of concanavalin A-Sepharose. Structural analysis by multiple-ion monitoring of partially methylated, alditol acetates derived from the various fractions indicated that the glycopeptides were separated according to the linkage pattern of mannose (see Fig. 1). 

Current detection limits are < 1 ng for full scan mass spectra and < 1 pg for multiple ion monitoring mass spectrometry. Compound identifications are based on the comparisons with authentic standards, GC retention time, literature mass spectra and the interpretation of mass spectrometric fragmentation patterns. The MS methods used for the various markers and studies are listed in Table 1. 

The combination of enantio-MDGC with high-resolution MS or mass-selective detectors, both used in full scan or (at least) in the multiple ion monitoring (MIM) mode is currently the most potent analytical tool in enantioselective analysis of chiral compounds from complex mixtures. 

Time-domain waveforms generated from a constant-phase Initial spectrum by the SWIFT procedure just described have been successfully applied to broad-band excitation, windowed excitation, and multiple-ion monitoring (11), and to mult1ple-1on ejection for enhancement of FT/ICR dynamic range (21) as described below. 

Lee, M. G. Millard, B. J. 1975. A comparison of unlabelled and labelled internal standards for quantification by single and multiple ion monitoring. /. Biomed. Mass Spectrom., 2,78-81. 

For positive identifications by GC/MS, the full mass spectrum of a tentatively identified component was compared to the mass spectrum of an authentic sample. If the spectra were identical, within experimental error, and if the gas chromatographic retention times of standard and unknown components on a 30-meter SE-54 fused silica capillary column agreed within two seconds, the identification was considered positive. When the amount of material present was insufficient for detection using full scan GC/MS techniques, the more sensitive single and multiple ion monitoring techniques were employed. Confirmation in these cases consisted of coincidences of retention times of mass chromatograms of the unknown and of the authentic sample. For chlorinated materials, the molecular ions contained additional information about the chlorine isotope distribution. Confirmation in those cases included the correct isotope... 

As mentioned previously, the formation of the methyl derivative is similar to several methods that already have been developed for organotin pesticides. The utilization of this derivative in conventional gas chromatographic residue procedures presents many challenges. Electron capture detection is sensitive enough but requires extensive clean-up while with FID and FPD the sensitivity is lower than desired. The development of a routine GC/MS procedure (single or multiple ion monitoring) was chosen then as the only possible alternative. A SIM (selective ion monitoring) method is specific for retention time and as well as for characteristic ions (m/e). 

In cases where low detection limits are required, single ion monitoring (SIM) or multiple ion monitoring (MIM) can be applied. Although less specific... 

Using SIFT-MS it is possible to record mass spectra in the full-scan mode (FS) of quadrupole MS or in multiple ion monitoring mode (MIM) when ions are passed thorough the quadrupole with a certain m/z ratio. FS mode allows the full mass spectrum of analytes in a defined range of m/z values to be registered within a specified time period. In the case of MIM, precursor ions and selected ions, formed during reaction of the reagent ion and the analyte, are scanned. 

Yao, M. et al., Rapid screening and characterization of drug metabolites using a multiple ion monitoring-dependent MS/MS acquisition method on a hybrid triple quadrupole-linear ion trap mass spectrometer, J. Mass Spectrom., 43(10), 1364, 2008. 

The application of GC-MS to PAH-analysis will allow considerable simplification of the work-up procedure. As far as solubility and dynamic range considerations will permit, the major PAH in airborne particulate matter samples can be accurately measured in the electron impact single or multiple ion monitoring mode, using the molecular ions of the respective PAH as specific ions, in the presence of much larger amounts of aliphatic hydrocarbons and carboxylic acids. Polar and ionic material is first removed from the combined benzene-methanol extract by liquid-liquid partition in water-diethylether. After drying, the addition of diazomethane results in derivatisation of the acidic components and the sample can be injected onto the column (Van Vaeck and Van Cauwenberghe (30)). 

Aqueous samples (0.5 ml) were mixed with 1 ml of acetonitrile containing 40 pg of pentafluorobenzaldehyde (PFB) and heated for 30 min at 85 °C. The reaction mixtures was cooled and, after addition of 0.5 ml of water, extracted with 10 ml of hexane. The organic layer was concentrated to I ml and analyzed by GC-MS or by GC with multiple-ion monitoring. Detection limits of lOppb could be obtained. For lower limits, 5 ml of aqueous sample and 10 ml of acetonitrile containing 0.5 mg of PFB were used. 

A QTRAP instrument is capable of a wide variety of scan modes full MS scan (MS), product ion scan (MS and MS ), PI scan, NL scan, MRM, predictive MRM (pMRM), multiple ion monitoring (MIM), enhanced multiply charged (EMC) scan and time-delayed fragmentation (TDF) (Hopfgartner et al., 2004 King and Fernandez-Metzler, 2006). Most of these scan modes can be incorporated into an IDA experiment to achieve metabolite detection and MS/MS spectral recording in a single run. 

Yao M, Ma L, Duchoslav E, Zhu M. Rapid screening and characterization of drug metabolites using multiple ion monitoring—depedent MS/MS scan and postacquisition data mining on a hybrid quadrupole—linear ion trap mass spectrometer. Rapid Commun Mass Spectrom 2009 23 1683-1693. 

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