Mass negative ionization

Electrospray is the softest mass spectrometry ionization technique and electrospray spectra therefore usually consist solely of molecular ions. Electrospray is unique, however, in that if the analyte contains more than one site at which protonation (in the positive-ion mode) or deprotonation (in the negative-ion mode) may occur, a number of molecular ions with a range of charge states is usually observed. For low-molecular-weight materials (< 1000 Da), the number of sites... 

Figure 5.62 Product-ion MS-MS spectra of the molecular ions from 8-hydroxy-2 -deoxyguanosine, obtained by (a) positive, and (b) negative ionization. Reprinted by permission of Elsevier Science from Comparison of negative- and positive-ion electrospray tandem mass spectrometry for the liquid chromatography-tandem mass spectrometry analysis of oxidized deoxynucleosides , by Hua, Y., Wainhaus, S. B., Yang, Y., Shen, L., Xiong, Y., Xu, X., Zhang, F. Bolton, J. L. and van Breemen, R. B., Journal of the American Society for Mass Spectrometry, Vol. 12, pp. 80-87, Copyright 2000 by the American Society for Mass Spectrometry.

A triple-quadrupole mass spectrometer with an electrospray interface is recommended for achieving the best sensitivity and selectivity in the quantitative determination of sulfonylurea herbicides. Ion trap mass spectrometers may also be used, but reduced sensitivity may be observed, in addition to more severe matrix suppression due to the increased need for sample concentration or to the space charge effect. Also, we have observed that two parent to daughter transitions cannot be obtained for some of the sulfonylurea compounds when ion traps are used in the MS/MS mode. Most electrospray LC/MS and LC/MS/MS analyses of sulfonylureas have been done in the positive ion mode with acidic HPLC mobile phases. The formation of (M - - H)+ ions in solution and in the gas phase under these conditions is favorable, and fragmentation or formation of undesirable adducts can easily be minimized. Owing to the acid-base nature of these molecules, negative ionization can also be used, with the formation of (M - H) ions at mobile phase pH values of approximately 5-7, but the sensitivity is often reduced as compared with the positive ion mode. 

Fig. 2.6 Titration assay of BSA and methyl orange (MO, MW 305 Da, Kj = 450 pM) by GPC spin column/ESI-MS methodology as a function of [MO]/[BSA] molar ratios in the positive ionization mode (A) and the negative ionization mode (B). The mass spectra in the top five panels are exploded...

ESI Mass Spectrometer ESI, APCI, Photodissociation, Positive/Negative Ionization... 

Fig. 2.12 ESI (negative ionization mode) mass spectral analysis of the GPC spin column eluate of a mixture containing ten known MMP-1 inhibitors (A) with MMP-1 and (B) without MMP-1 (background). The [M-H] ions for the ten compounds are indicated by solid circles ( ) on the spectra.

Fig. 2. 13 Negative ionization APCI mass spectra of the GPC spin column eluates of 20 pM 1 7jS-estradiol (MW 272 Da, Kj 1 nM) titrated with a variety of ER concentrations (1.25, 2.5, 5.0, 10.0, 20.0 pM). A miniature P6 CPC spin column was used with 10-pL samples, of which 2 pL was injected into the APCI TOP mass spectrometer under low flow...

Fig. 2.14 Positive and negative ionization ESI mass spectra of the CPC spin column eluates ofWY234 (MW 253 Da, IQ 1 pM), a weak non-covalent binder, with ER, initially prepared at a variety of [WY234]/[ER] molar ratios. A miniature P6 CPC spin column was used with 10 pL samples. The same absolute intensity scale is used for all panels. The masses and intensities of the peaks are labeled.

R. H. Negative ionization micro electrospray mass spectrometry of oligodeoxyribonucleotides and their complexes. Rapid Commun Mass Spectrom 1996, 10, 47-50. 

Dirtu AC, Roosens L, Geens T, Gheorghe A, Neels H, Covad A (2008) Simultaneous determination of bisphenol A, triclosan, and tetrabromobisphenol A in human serum using solid-phase extraction and gas chromatography-electron capture negative-ionization mass spectrometry. Anal Bioanal Chem 391 1175-1181... 

The analytical performance of four modes of LC-MS, multiple MS (MS"), and tandem MS operation (APCI and ESI with positive and negative ionizations) has been compared for two mass spectrometers, a triple-quadrupole and an ion-trap instrument.With 15 flavonoids as test compounds, the use of APCI in the negative-ion mode gave the best response, with the signal intensities and the mass-spectral characteristics not differing significantly between the two instruments. Under optimum conditions, full-scan limits of detection of... 

In the absence of tandem mass spectrometry equipment, almost equally reliable estimations of the PA concentrations can be made using gas chromatography-mass spectrometry (GC-MS). A standard quadrupole instrument, such as the one used for organic acid analysis, will be sufficient. Depending on the derivative, a choice between positive and negative ionization will have to be made. In general, a more extensive prepurification of the biological samples, will have to be realized. 

Each methylenethio unit adds three daltons to the peptide weight compared to the parent amide. Mass spectrometry can both confirm the expected mass as well as demonstrate preferred cleavages at both C—S bonds. In a linear pseudopeptide N-terminal or C-terminal fragments allow partial characterization of the location and sequence of the replacement by identification of the fragments using positive and negative ionization, respectively.t56 ... 

Yinon H.G. Boettger, Modification of a High-Resolution Mass Spectrometer for Negative Ionization , IntJMassSpectromlonPhys 10 (2) (1972) 73) M. Aubar J.T. Moseley, USP... 

During the analysis of PBDE in the particle phase of atmosphere samples from various sites in the United States, Hoh et al. [60] noticed a significant, unknown, bromine-containing gas chromatographic (GC) peak in some samples. To identify this unknown substance, full-scan mass spectra were obtained in both electron-impact and electron-capture negative ionization modes. Based on this analysis, it was suspected that this GC peak might be... 

Dearth, M.A., Hites, R.A., 1991a. Complete analysis of technical chlordane using negative ionization mass spectrometry. Environ. Sci. Technol. 25, 245-254. 

Fig. 5 Discovery metabolite profiling of brain tissue, where mass ion intensity ratios (FAAH / / FAAH+/+) of metabolites are presented on three-dimensional surface plots. Global view of the relative levels of metabolites in FAAH / and FAAH+/+ brains, plotted over a mass range of 200-1,200 m/z and liquid chromatography retention times of 0-105 min (plot shown for negative ionization mode). FAAH / brains possessed highly elevated levels of A-acyl ethanolamines (NAEs) (lipid group 4) and an unknown class of lipids (group 5), identified as A-acyl taurines (NATs). Other lipids, e.g., free fatty acids (group 1), phospholipids (group 2), and ceramides (group 3) were unaltered in these samples...

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