ESI/MS mass spectrum

Fig. 2.12.9. (a) FIA-ESI-MSC+) overview spectrum of cationic gemini surfactant lV,lV,lV,lV,-tetramethyl-lV,iV,-dicloclecyle-l,3-propane-cliyle-diammonium dibromide C12H25-N (CH3)2-CH2-CH2-CH2-N (CH3)2-C12H25 2Br- (b) FIA-ESI-MS(+) mass spectrum of cationic gemini surfactant as in (a) in the presence of methane sulfonic... 

Fig. 7.7 ESI-MS mass spectrum of the iridoid glycoside globularin, showing characteristic ions discussed in the text, i.e., [M+H]+ with m/z 493, [M + NH ] with tn/z 510, [M + Na] with m/z 515, and [M + K]+ with tn/z 531 as well as the adduct-bound dimers, i.e., [2M + NH4] with m/z 1002, [2M + Na]+ with m/z 1007, and [2M + K] with m/z 1023. The ions with m/z 131, 313, and 331 are fragment ions. (Reprinted from [163] with permission of Wiley copyright 2007, John Wiley and Sons, Ltd)...

Figure 1 Typical positive ESI-MS mass spectrum of Ginkgo biloba extract. ESI-MS, electrospray ionization mass spectrometry GA, ginkgolide A GB, ginkgolide B GC, ginkgolide C GJ, ginkgolide J. 

Figure 5 Typical positive ESI-MS mass spectrum of soybean extract. ESI-MS, electrospray ionization mass spectrometry. 

Next to this simple and straightforward approach, which can only be applied to relatively simple spectra with good signal-to-noise ratio (S/N), algorithms for the deconvolution or transformation of ESI-MS mass spectra of proteins were introduced [14] They use all the information available in the spectrum and provide good accuracies if other than protonated adducts are present. The software is readily available from the instrument manufacturers. 

FIGURE 2.3 (A) ESI-FTICR mass spectrum of a mixture of carbonic anhydrase II (CAII) and combinatorial library (289 components, 1). (B) MS-MS spectrum of the isolated complex of ions [CAII + Zn + 1] ". The expanded view shows the region of the singly charged inhibitors l , and the doubly expanded region shows the high resolution achieved in the experiment and the amino acid residue composition of the inhibitor ions. (Reprinted from Gao et al. [18], used with permission. Copyright 1996 by the American Chemical Society.)... 

Figure 12.16. ESI-MS/MS mass spectrum of PGD2. (Reproduced from ref. 59 by permission of Elsevier, copyright 2005.)...

ESI-MS has emerged as a powerful technique for the characterization of biomolecules, and is the most versatile ionization technique in existence today. This highly sensitive and soft ionization technique allows mass spectrometric analysis of thermolabile, non-volatile, and polar compounds and produces intact ions from large and complex species in solution. In addition, it has the ability to introduce liquid samples to a mass detector with minimum manipulation. Volatile acids (such as formic acid and acetic acid) are often added to the mobile phase as well to protonate anthocyanins. A chromatogram with only the base peak for every mass spectrum provides more readily interpretable data because of fewer interference peaks. Cleaner mass spectra are achieved if anthocyanins are isolated from other phenolics by the use of C18 solid phase purification. - ... 

Effect of dimer formation on deactivation. Another possible mode of deactivation is formation of inactive Co dimers or oligomers. To test for these species, we examined the ESI-mass spectram of fresh and deactivated Co-salen catalysts in dichloromethane solvent (22). The major peak in the mass spectram occurred at m/z of 603.5 for both Jacobsen s Co(II) and Co(III)-OAc salen catalysts, whereas much smaller peaks were observed in the m/z range of 1207 to 1251. The major feature at 603.5 corresponds to the parent peak of Jacobsen s Co(II) salen catalyst (formula weight = 603.76) and the minor peaks (1207 to 1251) are attributed to dimers in the solution or formed in the ESI-MS. The ESI-MS spectrum of the deactivated Co-salen catalyst, which was recovered after 12 h HKR reaction with epichlorohydrin, was similar to that of Co(II) and Co(III)-OAc salen. Evidently, only a small amount of dimer species was formed during the HKR reaction. However, the mass spectram of a fresh Co(III)-OAc salen catalyst diluted in dichloromethane for 24 h showed substantial formation of dimer. The activity and selectivity of HKR of epichlorohydrin with the dimerized catalyst recovered after 24 h exposure to dichloromethane were similar to those observed with a fresh Co-OAc salen catalyst. Therefore, we concluded that catalyst dimerization cannot account for the observed deactivation. 

Applications With the current use of soft ionisation techniques in LC-MS, i.e. ESI and APCI, the application of MS/MS is almost obligatory for confirmatory purposes. However, an alternative mass-spectrometric strategy may be based on the use of oaToF-MS, which enables accurate mass determination at 5 ppm. This allows calculation of the elemental composition of an unknown analyte. In combination with retention time data, UV spectra and the isotope pattern in the mass spectrum, this should permit straightforward identification of unknown analytes. Hogenboom et al. [132] used such an approach for identification and confirmation of analytes by means of on-line SPE-LC-ESI-oaToFMS. Off-line SPE-LC-APCI-MS has been used to determine fluorescence whitening agents (FWAs) in surface waters of a Catalan industrialised area [138]. Similarly, Alonso et al. [139] used off-line SPE-LC-DAD-ISP-MS for the analysis of industrial textile waters. SPE functions here mainly as a preconcentration device. 

Schmitt [17] in his book on the analysis of surfactants includes details of a number of HPLC-based procedures. LC-MS can be used for positive identification. Figure 29 shows the molecular ion mass spectrum for the surfactant lauryl hydrogen sulfate detectable as its (M—H) ion by positive ESI. 

Figure 4.14 Mass spectrum obtained by ESI MS of beeswax in the mass range m/z 800 1000 and mass spectrum obtained by ESI MS/MS of hexacosanediol 1,15 dipalmitoyl. Adapted from Gamier et al., 2002...

A similar analysis of cochineal can be performed with the use of CE with ESI MS detection. The results are similar to those obtained with HPLC MS.[20] In the lac dye extract, the signal of laccaic acid A is found in the mass spectrum as the dominant one at m/ z 536. However, a second peak is observed on the electropherogram, and the eluted substance can be identified as laccaic acid E, on account of the mass spectrum which consists of the following signals at m/z 494 [M H], 476 [M H20 H] and 450 [M C02 H]. ... 

The soft API techniques such as APCI and ESI, which are predominantly applied nowadays fulfil the most desirable criteria for an ionisation method in MS-MS, especially for mixture analysis, where each compound contained in the mixture produce as few—ideally only one—ions of different mass-to-charge ratio (m/z) as possible upon ionisation. The result would be a quite simple FIA-MS overview spectrum with few interferences in the parent ion to be selected... 

Fig. 2.6.1. RP-LC-ESI-MS analysis of flocculation sludge from a Barcelona drinking water treatment plant. Column Cig LiChrolute 250 X 4.6 mm, 5 pm, gradient elution with ACN-water. Upper trace total ion current (TIC), lower traces extracted ion chromatograms for NPEOs, raE0 = 1-5. Inset ESI mass spectrum of NPEO oligomeric mixture.

A rapid technique for the identification of surfactants in consumer products by ESI-MS was proposed by Ogura and co-workers [6], After a simple preparation procedure, infusion of the sample, which was prepared in a water/methanol mixture (50 50) containing 10 mM ammonium acetate, allowed assignment of the [M + NH4]+ ions of Cio- and Ci2-mono- and -diglucoside in the mass spectrum (ion masses as in Table 2.7.1). The approach even permitted quantitative analysis when deuterated internal standards were used. 

Fig. 2.9.6. (Inset) ESI-FIA-MS(+) overview spectrum of (a) PEG homologues and (b) PPG homologues contained in wastewater effluent SPE extract (7) ESI-LC-MS(+) RIC and selected mass traces of (l)-(3) PEG and (4)-(6) PPG homologues from mixture of (a) and (b) CiS-SPE with selective elution, compounds ionised as [M + NH4]+...

Fig. 2.9.26. ESI-FIA-MS-MS(-I-) (CID) product ion mass spectrum of [M + NH4]+ parent ion of fatty acid polyglycolester surfactant blend (C H2 +i-C(0)-0-(CH2-CH2-0)m-H) selected ion under CID m/z 406 fragmentation behaviour in the inset [24],...

Fig. 2.9.27. ESI-FIA-MS-MS(+) (CID) parent ion mass spectrum of product ion at m/z 283 of Cig-SPE extract presenting fatty acid polyglycolester characteristic ions at m jz 406, 450, 494, 538 and 582, all equally spaced with A m/z 44 [16].

Fig. 2.9.31. ESI-FIA-MS-MS(+) (CID) product ion mass spectrum of parent ion with m/z 244 of FAMA homologue (C H2 +1-C(0)-N(H)-CH2-CH2-0H n = 11) (inset) fragmentation scheme observed under CID conditions [24].

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