Electrospray ionization analysis

Eor direct characterization of disubstituted piperidine alkaloids in extracts of L. inflata, tandem mass spectrometric method was developed using electrospray ionization. Analysis was performed in positive ion mode on a triple quadropole LC/MS system. The identification and structural elucidation of the alkaloids were performed by comparing their changes in molecular mass (AM), full-scan MS-MS spectra with those of lobeline, lobelanine, norlobelanine, and lobelanidine. These alkaloids and ten other derivatives were identified in the plant extracts. 

Electrospray ionization. Analysis was demonstrated using electrospray ionization of HPLC effluent. Efficiency of ionization varies between PEG, monoester, and diester, so the MS signal is not suitable for use in quantification (91). 

Two relatively new techniques, matrix assisted laser desorption ionization-lime of flight mass spectrometry (MALDI-TOF) and electrospray ionization (FS1), offer new possibilities for analysis of polymers with molecular weights in the tens of thousands. PS molecular weights as high as 1.5 million have been determined by MALDI-TOF. Recent reviews on the application of these techniques to synthetic polymers include those by Ilantoif54 and Nielen.555 The methods have been much used to provide evidence for initiation and termination mechanisms in various forms of living and controlled radical polymerization.550 Some examples of the application of MALDI-TOF and ESI in end group determination are provided in Table 3.12. The table is not intended to be a comprehensive survey. 

The fundamental piece of information on which the subsequent spectral analysis is based is the total-ion-current (TIC) trace. Such a trace, obtained from the LC-MS analysis of a pesticide mixture, is shown in Figure 3.13, together with the UV trace recorded simultaneously. For the purposes of this discussion, the HPLC and MS conditions used to generate the data, other than the fact that electrospray ionization was used, are irrelevant. 

The suppression effects associated with electrospray ionization have been discussed earlier although if the compounds present are similar in behaviour these may be minimal. The intention, when using chromatography as an introduction device, is to allow individual components to enter the mass spectrometer for analysis. The separation capability of HPLC has been discussed previously and it is not unusual, particularly when complex mixtures are being studied, to encounter electrospray spectra from more than one component. 

The polarity and thermal instability of biopolymers, together with the almost exclusive formation of singly charged ions renders APCl an inappropriate ionization technique for their study. Much of the early work involving electrospray ionization, on the other hand, was connected with the analysis of this type of molecule, in particular determining the molecular weight of proteins for which it is particularly effective. 

MALDI-ToF is a technique that allows the molecular weights of proteins and peptides to be determined. It is less susceptible to suppression effects than electrospray ionization and thus is able to be used for the direct analysis of mixtures. In the case of a crude tryptic digest, MALDI-ToF will provide a molecular weight profile of the polypeptides present without the analysis time being extended by the need to use some form of chromatographic separation. 

A method has been reported for the quantification of five fungicides (shown in Figure 5.39) used to control post-harvest decay in citrus fruits to ensure that unacceptable levels of these are not present in fruit entering the food chain [26]. A survey of the literature showed that previously [27] APCl and electrospray ionization (ESI) had been compared for the analysis of ten pesticides, including two of the five of interest, i.e. carbendazim and thiabendazole, and since it was found that APCl was more sensitive for some of these and had direct flow rate compatibility with the HPLC system being used, APCl was chosen as the basis for method development. 

Paganga, G. et al.. The polyphenolic content of fruit and vegetables and their antioxidant activities what does a serving constitute Free Radical Res., 30, 153, 1999. Maatta, K.R. et al.. High-performance liquid chromatography (HPLC) analysis of phenolic compounds in berries with diode array and electrospray ionization mass spectrometric (MS) detection Rihes species, J. Agric. Food Chem., 51, 6736, 2003. 

The most recent progress in MS analysis of chlorophylls has been obtained with the development of atmospheric ionization methods such as atmospheric pressure chemical ionization (APCl) and electrospray ionization (ESI). These techniques have demonstrated much more sensitivity than thermospray ionization, detecting chloro-... 

Tian, Q. et al., Screening for anthocyanins using high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry with precursor-ion analysis, product-ion analysis, common-neutral-loss analysis, and selected reaction monitoring, J. Chromatogr. A, 1091, 72, 2005. 

Electrospray ionization (ESI) and APCI are the two popular API techniques that will be discussed here. The applications to the analysis of pesticides that will be discussed include imidazolinone herbicides, phenoxy acid herbicides, and A-methyl carbamate insecticides. Matrix effects with respect to quantitation also will be discussed. Eor the... 

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... 

Wunschel, D. S. Pasa-Tolic, L. Feng, B. B. Smith, R. D. Electrospray ionization Fourier transform ion cyclotron resonance analysis of large polymerase chain reaction products. J. Am. Soc. Mass Spectrom. 2000,11, 333-337. 

Different mass analysers can be combined with the electrospray ionization source to effect analysis. These include magnetic sector analysers, quadrupole filter (Q), quadrupole ion trap (QIT), time of flight (TOF), and more recently the Fourrier transform ion cyclotron resonance (FTICR) mass analysers. Tandem mass spectrometry can also be effected by combining one or more mass analysers in tandem, as in a triple quadrupole or a QTOF. The first analyzer is usually used as a mass filter to select parent ions that can be fragmented and analyzed by subsequent analysers. 

Fang, J. Barcelona, M. J. Structural determination and quantitative analysis of bacterial phospholipids using liquid chromatography electrospray ionization mass spectrometry./. Microbiol. Meth. 1998,33,23-35. 

Wang, W. Liu, Z. Ma, L. Hao, C. Liu, S. Voinov, V. G. Kalinosvskaya, N. I. Electrospray ionization multiple-stage tandem mass spectrometric analysis of digycosyldiacylglycerol glycolipids from the bacteria Bacillus pumilus. Rapid Comm. Mass Spectrom. 1999,13,1189-1196. 

Dunlop, K. Y. Li, L. Automated Mass Analysis of low-molecular-mass bacterial proteome by liquid chromatography-electrospray ionization mass spectrometry. J. Chromatogr. A 2001, 925,123-132. 

Schneiter, R. Brugger, B. Sandhoff, R. Zellnig, G. Leber, A. Lampl, M. Athenstaedt, K. Hrastnik, C. Eder, S. Daum, G. Paltauf, F. Wieland, F. T. Kohlwein, S. D. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) analysis of the lipid molecular species composition of yeast subcellular membranes reveals acyl chain-based sorting/remodeling of distinct molecular species en route to the plasma membrane. J. Cell Biol. 1999,146,741-754. 

Jiang, Y. Hofstadler, S. A. A highly efficient and automated method for purifying and desalting PCR products for analysis by electrospray ionization mass spectrometry. Anal. Biochem. 2003,316,50-57. 

Ivanov, A.R., Zang, L., Karger, B. L. (2003). Low-attomole electrospray ionization MS and MS/ MS analysis of protein tryptic digests using 20 pm-i.d. polystyrene-divinylbenzene monolithic capillary columns. Anal. Chem. 75, 5306-5316. 

Racaityte, K., Lutz, E.S.M., Unger, K.K., Lubda, D., Boos, K.S. (2000). Analysis of neuropeptide Y and its metabolites by high-performance liquid chromatography—electrospray ionization mass spectrometry and integrated sample cleanup with a novel restricted-access sulphonic acid cation exchanger. J. Chromatogr. A 890, 135-144. 

Liu, H. J., Berger, S. J., Chakrahorty, A. B., Plumh, R. S., Cohen, S. A. (2002). Multidimensional chromatography coupled to electrospray ionization time-of-fhght mass spectrometry as an alternative to two-dimensional gels for the identification and analysis of complex mixtures of intact proteins. J. Chromatogr. B 782(1-2), 267-289. 

Tang, Q., Harrata, A. K., Lee, C. S. (1997). Two-dimensional analysis of recombinant E. coli proteins using capillary isoelectric focusing electrospray ionization mass spectrometry. Anal. Chem. 69(16), 3177-3182. 

Blonder, J., Rodriguez-Galan, M.C., Chan, K.C., Lucas, D.A., Yu, L.R., Conrads, T.P, Issaq, H. J., Young, H.A., Veenstra, T.D. (2004). Analysis of murine natural killer cell microsomal proteins using two-dimensional liquid chromatography coupled to tandem electrospray ionization mass spectrometry. J. Proteome Res. 3, 862-870. 

FIGURE 13.4 Total ion chromatograms from the ID LC/MS analysis of a yeast ribosomal protein fraction separated using 0.1% TFA (Panel a) and 0.1% formic acid (Panel b) as mobile phase modifiers. TFA produced narrower, more concentrated, peaks for mass analysis that did not overcome the significant electrospray ionization suppression associated with using this modifier for LC/MS studies, resulting in an overall reduction in component intensities. 

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