LC/ESI

Kato, S., Oba, Y., Ojika, M., and Inouye, S. (2004). Identification of the biosynthetic units of Cypridina luciferin in Cypridina (Vargula) hilgen-dorfii by LC/ESI-TOF-MS. Tetrahedron 60 11427-11434. 

Schultz MM, Furlong ET (2008) Trace analysis of antidepressant pharmaceuticals and then-select degradates in aquatic matrixes by LC/ESI/MS/MS. Anal Chem 80 1756-1762... 

Figure 5.31 LC-electrospray-MS-MS spectrum of the column eluate at around 22 min in the analysis of the peptide mixture from the tryptic digest of glycoprotein TIME-EA4 from silkworm diapause eggs. Reprinted from Bioorg. Med. Chem., 10, Kurahashi, T., Miyazaki, A., Murakami, Y., Suwan, S., Franz, T., Isobe, M., Tani, M. and Kai, H., Determination of a sugar chain and its linkage site on a glycoprotein TIME-EA4 from silkworm diapause eggs by means of LC-ESI-Q-TOF-MS and MS/MS , 1703-1710, Copyright (2002), with permission from Elsevier Science.

Recently, 19 diarylheptanoids, of which 6 are new, were separated and identified in turmeric by LC-ESI-MS/MS coupled to a DAD detector. More than 20 compounds were identified in the volatile oil extracted from turmeric by different meth-... 

Carmona, M. et al., Crocetin esters, picrocrocin and its related componnds present in Crocus sativus stigmas and Gardenia jasminoides frnits. Tentative identification of seven new compounds by LC-ESI-MS, J. Agric. Food Chem., 54, 973, 2006. 

Rentel, C. et al.. Silver-plated vitamins a method of detecting tocopherols and carotenoids in LC/ESI-MS coupling. Ana/. Chem., 70, 4394, 1998. 

Tomoyuki, O. et al., Determination of acylated anthocyanin in human urine after ingesting a purple-fleshed sweet potato beverage with various contents of anthocyanin by LC-ESI-MS/MS, Biosci. Biotechnol Biochem., 70, 2540, 2006. 

The fenoxycarb recoveries for orange, onion, grape, and tomato samples ranged from 63 to 70%. The LOQ and LOD were 0.01 mg kg and 0.005 mg kg , respectively, when using liquid chromatography/electrospray ionization mass spectrometry (LC/ESI/MS). 

Liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS)... 

Water samples, received from the respective groundwater trials, are analyzed by direct aqueous injection (DAI) by LC/ESI-MS/MS. A 1-mL volume of the water is pipetted into a 1.8-mL autosampler vial. The internal standard solution is added (200 qL) and mixed. The vials are capped and analyzed by LC/ESI-MS/MS using the selected reaction monitoring (SRM) mode. 

Prepare a calibration curve in the following manner. Measure 1 mL of control water into a series of 1.8-mL autosampler vials. Fortify each water sample with 200 o.L of the appropriate calibration standard to make a 0.1, 0.5 and 2.5ngmL calibration curve. Mix the sample by vortexing or shaking the vial and analyze 200 iL by LC/ESI-MS/MS. For well and lysimeter water, mix 1 mL of sample water with 200 uL of the lOngmL" mixed internal standard solution in a 1.8-mL autosampler vial, cap the vial, mix the contents and analyze 200 iL by LC/ESIMS/MS. 

Applications of hyphenated ESI mass-spectrometric techniques are described elsewhere LC-ESI-MS (Section 73.3.2), SFC-ESI-MS (Section 73.2.2) andCE-ESI-MS (Section 73.6.1) for polar nonvolatile organics. 

In direct insertion techniques, reproducibility is the main obstacle in developing a reliable analytical technique. One of the many variables to take into account is sample shape. A compact sample with minimal surface area is ideal [64]. Direct mass-spectrometric characterisation in the direct insertion probe is not very quantitative, and, even under optimised conditions, mass discrimination in the analysis of polydisperse polymers and specific oligomer discrimination may occur. For nonvolatile additives that do not evaporate up to 350 °C, direct quantitative analysis by thermal desorption is not possible (e.g. Hostanox 03, MW 794). Good quantitation is also prevented by contamination of the ion source by pyrolysis products of the polymeric matrix. For polymer-based calibration standards, the homogeneity of the samples is of great importance. Hyphenated techniques such as LC-ESI-ToFMS and LC-MALDI-ToFMS have been developed for polymer analyses in which the reliable quantitative features of LC are combined with the identification power and structure analysis of MS. 

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. 

ESI and APCI are soft ionisation techniques which usually result in quasi-molecular ions such as [M + H]+ with little or no fragmentation molecular weight information can easily be obtained. However, experimental conditions can also be chosen in such a way that a sufficiently characteristic pattern is obtained, allowing verification [540]. ESI is amenable to thermally labile and nonvolatile molecules. Both ESI and APCI are much more sensitive than PB and very well suited for quantitative analysis, but less so for unknown samples. The choice among the two is usually determined by the application. Recently, nanoscale LC-ESI-MS has been developed [541]. The nano-electrospray ion source offers the highest sensitivity available for LC-MS (atto-to femtomole range) and can also be used as an off-line ion source. 

Many excellent reviews on the development, instrumentation and applications of LC-MS can be found in the literature [560-563]. Niessen [440] has recently reviewed interface technology and application of mass analysers in LC-MS. Column selection and operating conditions for LC-MS have been reviewed [564]. A guide to LC-MS has recently appeared [565]. Voress [535] has described electrospray instrumentation, Niessen [562] reviewed API, and others [566,567] have reviewed LC-PB-MS. For thermospray ionisation in MS, see refs [568,569]. Nielen and Buytenhuys [570] have discussed the potentials of LC-ESI-ToFMS and LC-MALDI-ToFMS. Miniaturisation (reduction of column i.d.) in LC-MS was recently critically evaluated [571]. LC-MS/MS was also reviewed [572]. Various books on LC-MS have appeared [164,433,434,573-575], some dealing specifically with selected ionisation modes, such as CF-FAB-MS [576] or API-MS [577],... 

Electrospray has been successful for numerous azo dyes that are not ionic salts. Several anthraquinone dyes have been analysed by LC-ESI-MS [552]. Electrospray achieves the best sensitivity for compounds that are precharged in solution (e.g. ionic species or compounds that can be (de)protonated by pH adjustment). Consequently, LC-ESI-MS has focused on ionic dyes such as sulfonated azo dyes which have eluded analysis by particle-beam or thermospray LC-MS [594,617,618]. Techniques like LC-PB-MS and GC-MS, based on gas-phase ionisation, are not suitable for nonvolatile components such as sulfonated azo dyes. LC-TSP-MS on... 

Online LC-ESI-TOF-MS experiments are carried out in a very similar fashion to the off-line NPS-HPLC separations described above, with a few notable exceptions. Firstly, 0.3% (v/v) formic acid is added to each mobile phase to counteract the ionization suppression induced by TFA. Because of the formic acid UV detection must be carried out at 280 nm (as opposed to 214 nm). To aid in normalization between runs 1 jag of Bovine insulin (MW = 5734 Da) is added to each chromatofocusing fraction prior to injection onto the column. Finally, the flow is split postcolumn directing 200 JlL/min into the ion source and the remaining 300 JlL/min through the UV detector and fraction collection. 

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