Selectivity analysis spectrometry

Tandem mass spectrometry or ms/ms was first introduced in the 1970s and gained rapid acceptance in the analytical community. The technique has been used for stmcture elucidation of unknowns (26) and has the abiUty to provide sensitive and selective analysis of complex mixtures with minimal sample clean-up (27). Developments in the mid-1980s advancing the popularity of ms/ms included the availabiUty of powerhil data systems capable of controlling the ms/ms experiment and the viabiUty of soft ionisation techniques which essentially yield only molecular ion species. 

As in HPLC, the coupling of MS detection with CE has provided an excellent opportunity for more selective analysis, but the much reduced flow rates, small injection volumes, limitations in the types of buffers used [since electrospray ionization (ESI) is used in capillary electrophoresis/mass spectrometry (CE/MS)], and need to... 

Vreeken, R.J., P. Speksnijder, I. Bobeldijk-Pastorova, et al. 1998. Selective analysis of the herbicides gly-phosate and aminomethylphosphonic acid in water by on-line solid-phase extraction-high-performance liquid chromatography-electrospray ionization mass spectrometry. J. Chromatogr. A 794 187-199. 

A remarkably selective conversion of formaldehyde into glucose was reported by Weiss and co-workers.The reaction, carried out at 98°, was initiated by adding aqueous sodium hydroxide to a calcium chloride-formaldehyde solution. Under these conditions the induction period was IS seconds, and at 18% formaldehyde conversion level hexoses were formed with 84.3% selectivity. Analysis by glc of the products [in the form of trimethyl silyl (TMS) derivatives] revealed that no branched sugars were formed and glucose constituted about 90% of the reaction mixture. It should be noted that analysis—gas chromatography-mass spectrometry (gc-ms) of the corresponding alditol acetates—of the mixtures obtained in the formose reaction carried out under normal conditions revealed the presence of 33-37 components. ... 

Zaima, N., Goto-Inoue, N., Adachi, K., and Setou, M. 2011. Selective analysis of lipids by thin-layer chromatography blot matrix-assisted laser desorption/ionization imaging mass spectrometry, J. Oleo ScL, 60 93-98. 

Bieri S, Ilias Y, Bicchi C, Veuthey J-L, Christen P (2006) Focused microwave-assisted extraction combined with solid-phase microextraction and gas chnunatography-mass spectrometry for the selective analysis of cocaine from coca leaves. J Chromatogr A 1112... 

For example, by using the nanostructure-initiator mass spectrometry, Patti and colleagues [130] detected intact cholesterol and its derivative molecules in situ to provide the first images of brain sterol localization in a knockout mouse model of 7-dehydrocholesterol reductase. Other nanomaterials (e.g silver nanoparticles) have also been used to analyze lipids directly from tissue samples [133], From a thin film of colloidal graphite on rat brain tissue, direct lipid profiling was performed by graphite-assisted laser desorption/ionization mass spectrometry, which allowed to detect 22 HexCer species, whereas only eight HexCer species are detected with MALDI-TOF/MS [132], Chemically selective analysis for HexCer and ST species was successfully obtained. 

In order to reduce or eliminate off-line sample preparation, multidimensional chromatographic techniques have been employed in these difficult analyses. LC-GC has been employed in numerous applications that involve the analysis of poisonous compounds or metabolites from biological matrices such as fats and tissues, while GC-GC has been employed for complex samples, such as arson propellants and for samples in which special selectivity, such as chiral recognition, is required. Other techniques include on-line sample preparation methods, such as supercritical fluid extraction (SFE)-GC and LC-GC-GC. In many of these applications, the chromatographic method is coupled to mass spectrometry or another spectrometiic detector for final confirmation of the analyte identity, as required by many courts of law. 

Figure 15.8 Multidimensional GC-MS separation of urinary acids after derivatization with methyl chloroformate (a) pre-column cliromatogram after splitless injection (h) Main-column selected ion monitoring cliromatogram (mass 84) of pyroglutamic acid methyl ester. Adapted from Journal of Chromatography, B 714, M. Heil et ai, Enantioselective multidimensional gas chromatography-mass spectrometry in the analysis of urinary organic acids , pp. 119-126, copyright 1998, with permission from Elsevier Science.

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