Phase-system switching

Figure 11.16 Chromatograms of plasma samples obtained by using SPE-SFC with super-aitical desorption of the SPE cartridge (a) blank plasma (20 p.1), UV detection at 215 nm (b) blank plasma (20 p.1), UV detection at 360 nm (c) plasma (1 ml) containing 20 ng mitomycin C (MMC), UV detection at 360 nm. Reprinted from Journal of Chromatography, 454, W. M. A. Niessen et al., Phase-system switching as an on-line sample pretreatment in the bioanalysis of mitomycin C using supercritical fluid cliromatography, pp. 243-251, copyright 1988, with permission from Elsevier Science.

A well-known method for peak tracking is based on the phase-system switching idea, " which was developed to solve problems of mobile phase incompatibility in LC/MS target compound analysis. An analytical column is usually connected to a trapping column in tandem mode. A switching valve is placed after the UV detector, and the flow of nonvolatile eluents is directed through the trapping column to waste. When the peak of interest elutes from the analytical column it is... 

W. M. A. Niessen, P. J. M. Bergers, U. R. Tjaden and J. van der Greef, Phase-system switching as an on-line sample pretreatment in the bioanalysis of mitomycin C using supercritical fluid chromatography , J. Chromatogr. 454 243 -251 (1988). 

A quantitative bioassay for erythromycin 2 -ethylsuccinate (EM-ES, M, 861 Da), a prodrug of the macrolide antibiotic erythromycin, using Cf-FAB LC-MS was described by Kokkonen et al. [53-54]. Reversed-phase LC of extracted plasma samples was performed at a flow-rate of 1 ml/min. In order to meet the flow-rate requirements of the Cf-FAB interface, i.e., 15 pl/min, without splitting, the phase-system switching approach [53] was used. After post-column dilution of the column effluent with water, the eluent fraction of interest was enriched on a short precolumn, from which the compound of interest was desoibed and transferred to the Cf-FAB interface probe. A [ Hj]-analogue was used as internal standard. Good linearity was observed in the range of 0.1 to 10 pg/ml EM-ES in plasma. The within-ran precision was ca. 6%. The accuracy and inter-day precision, determined at 1.05 pg/ml in plasma, were 0.93 0.11 pg/ml and 12%, respectively (n=6). The determination limit was 0.1 pg/ml [54]. 

P. Kokkonen, W.M.A. Niessen, U.R. Tjaden, J. van der Greef, Phase-system switching in Cf-FAB LC-MS, Rapid Commun. Mass Spectrom., 5 (1991) 19. 

Nevertheless, Figure 5 demonstrates that the enantiomeric separation using a phosphate buffer in the mobile phase can be coupled via the PSS approach on-line to an LC/MS moving belt interface. Other examples of the PSS approach or similar procedures with other compounds and other LC/MS interfaces have been described (2, 9-14). Besides the actual phase-system switching, which enables the choice of the most favorable solvent for a particular interface, the PSS approach offers some other features as well. The desorption flow-rate used can be adjusted to the capabilities of the LC/MS interface applied. While in the present example with the moving belt a flow-rate of 0.4 ml/min of methanol was used, desorption has also been demonstrated with 1.2 ml/min for a thermospray interfaced),... 

Figure 4. Schematic diagram of the phase-system switching approach applied in the moving belt LC/MS analysis of metropolol enantiomers. AC=analytical column, UV=UV-detector, ACN=desorbing eluent (see text), and TC=trapping column.

Figure 5. Peaks of the (+)- and (-)-metoprolol enantiomers after chiral separation, phase-system switching and moving belt LC/MS. Conditions see text.

Walhagen A, Edholm L-E, Heeremans GEM et at (1989) Coupled-column chromatography-mass spectrometry. Thermospray liquid chromatographic-mass spectrometric and liquid chromatographic-tandem mass spectrometric analysis of metoprolol enantiomers in plasma using phase-system switching. Journal of Chromatography 474 257. 

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