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Chromatography/negative Electrospray Ionization Tandem Mass Spectrometry (negative + electrospray_ionization_tandem_mass_spectrometry)
Selected AbstractsQuantitation of methylated hemoglobin adducts in a signature peptide from rat blood by liquid chromatography/negative electrospray ionization tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2008Fagen Zhang Hemoglobin adducts are often used as biomarkers for exposure to reactive chemicals in toxicology studies. Therefore, fast, sensitive, accurate, and reproducible methods for quantifying these protein adducts are key to evaluate test material dosimetry. A methodology has been developed for the quantitation of methylated hemoglobin adducts isolated from rats exposed to the model alkylating agent: methyl methane sulfonate (MMS). After 4 days of MMS exposure by oral gavage, hemoglobin was isolated from rat blood and digested with trypsin. The tryptic digestion solution was used for the adducted hemoglobin signature peptide quantitation via liquid chromatography/negative tandem mass spectrometry (LC/ESI-MS/MS). The limit of quantitation (LOQ) for the methylated hemoglobin beta chain N-terminal signature peptide (MeVHLTDAEK) was 1.95,ng/mL (5.9,pmol/mg globin). The calibration curves were linear over a concentration range of 1.95 to 625,ng/mL, with a correlation coefficient R2 >0.998, accuracy of 85.8 to 119.3%, and precision of 0.9 to 19.4%. Copyright © 2008 John Wiley & Sons, Ltd. [source] Quantitative analysis of amyloid , peptides in cerebrospinal fluid of Alzheimer's disease patients by immunoaffinity purification and stable isotope dilution liquid chromatography/negative electrospray ionization tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2006Tomoyuki Oe The 40 and 42 amino-acid residue forms of amyloid beta (A,1,40 and A,1,42) in cerebrospinal fluid (CSF) have been proposed as potential biomarkers of Alzheimer's disease (AD). Quantitative analyses of A, peptides in CSF have relied almost exclusively on the use of immunoassay-based assays such as the enzyme-linked immunosorbent assay (ELISA) procedure. However, due to the ability of the A, peptides to readily self-aggregate or bind to other proteins and glassware, such analyses are extremely challenging. Analyses are further complicated by the potential of the peptides to undergo post-translational modifications and the possibilities for cross-reaction in the ELISA assays with endogenous components of the CSF. An approach based on liquid chromatography/tandem mass spectrometry (LC/MS/MS) has now been developed which overcomes these methodological issues. The key steps in implementing this new approach involved immunoaffinity purification coupled with the use of [15N]-labeled A, peptides as internal standards, a basic LC mobile phase, negative ion electrospray ionization, and a basic solvent for dissolving the peptides and washing the injection needle to prevent carryover of analytes during multiple injections on the LC/MS system. The validated method had limits of quantitation of 44,fmol/mL (200,pg/mL) for A,1,42 and 92,fmol/mL (400,pg/mL) for A,1,40. An excellent correlation was found between the LC/MS/MS assay and an ELISA assay for A,1,42 in human CSF (r2,=,0.915), although less correlation was observed for A,1,40 (r2,=,0.644). Mean CSF A,1,42 concentrations for samples collected 2 weeks apart from a limited number of AD patients provided additional confidence in the reproducibility of the LC/MS/MS assay. Concentrations for duplicate samples from AD patients were slightly higher than most previously reported values (mean 1.06,±,0.25,ng/mL; n,=,7). A,1,40 concentrations in duplicate samples obtained from AD patients were also reproducible but were found to be slightly lower than most previously reported values (mean 6.36,±,3.07,ng/mL; n,=,7). Consistent with literature reports, mean A,1,42 concentrations were found to be lower in AD patients compared with the normal subjects (mean 1.49,±,0.59,ng/mL; n,=,7), whereas there was no difference in A,1,40 concentrations between AD patients and normal subjects (mean 5.88,±,3.03,ng/mL; n,=,7). The accuracy and precision of the LC/MS assay mean that it will be a useful complement to existing ELISA assays for monitoring therapeutic interventions designed to modulate CSF A,1,42 concentrations in individual AD patients. Moreover, the introduction of stable isotope labeled internal standards offers the potential to achieve a more rigorous account of the influence of methodological effects related to sample collection and processing. Copyright © 2006 John Wiley & Sons, Ltd. [source] Study of the reaction products of flavonols with 2,2-diphenyl-1-picrylhydrazyl using liquid chromatography coupled with negative electrospray ionization tandem mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 12 2004Erlend Hvattum Abstract The products obtained after the reaction between flavonols and the stable free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH,) in both methanol and acetonitrile were characterized using liquid chromatography coupled with negative electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) and NMR spectroscopy. The flavonols studied were quercetin, kaempferol and myricetin. In methanol, two reaction products of oxidized quercetin were identified using LC/ESI-MS/MS and NMR. Quercetin was oxidized through a transfer of two H-atoms to DPPH, and subsequently incorporated either two CH3OH molecules or one CH3OH- and one H2O molecule giving the products 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy-2,3-dimethoxy-2,3-dihydrochromen-4-one and 2-(3,4-dihydroxyphenyl)-3,3,5,7-tetrahydroxy-2-methoxy-2,3-dihydrochromen-4-one, respectively. LC/ESI-MS/MS analysis revealed that in methanol, kaempferol and myricetin also gave rise to methoxylated oxidation products similar to that identified for quercetin. Kaempferol, in addition, also exhibited products where a kaempferol radical, obtained by a transfer of one H-atom to DPPH,, reacted with CH3OH through the addition of CH3O,, yielding two isomeric products. When the reaction took place in acetonitrile, LC/ESI-MS/MS analysis showed that both quercetin and myricetin formed stable isomeric quinone products obtained by a transfer of two H-atoms to DPPH,. In contrast, kaempferol formed two isomeric products where a kaempferol radical reacted with H2O through the addition of OH,, i.e. similar to the reaction of kaempferol radicals with CH3OH. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||