Flow-injection analysis-mass spectrometry applications

Another current trend that is well underway is the use of more specific analytical instrumentation that allows less extensive sample preparation. The development of mass spectrometric techniques, particularly tandem MS linked to a HPLC or flow injection system, has allowed the specific and sensitive analysis of simple extracts of biological samples (68,70-72). A similar HPLC with UV detection would require significantly more extensive sample preparation effort and, importantly, more method development time. Currently, the bulk of the HPLC-MS efforts have been applied to the analysis of drugs and metabolites in biological samples. Kristiansen et al. (73) have also applied flow-injection tandem mass spectrometry to measure sulfonamide antibiotics in meat and blood using a very simple ethyl acetate extraction step. This important technique will surely find many more applications in the future. 

The content of this chapter focuses on the analysis of intact polar lipids by high-pressure liquid chromatography (HPLC) with flow or loop injection -and mass spectrometry (MS) or tandem mass spectrometry (MS-MS) using thermospray (TS), discharge-assisted TS [or plasmaspray (PSP)], electrospray (ES) and atmospheric pressure chemical ionization (APCI). It was intended to include only those papers describing the analysis of intact polar lipids by liquid chromatography on-line with MS. However, many papers describe flow or loop injection with MS and/or the analysis of derivatives of polar lipids. These papers, describing excellent applications of MS and/or MS-MS of polar lipids, are included since this chapter would not have been complete without them. 

Centineo, G., Bayon, M. M., and Sanz-Medel, A. (2000) Flow injection analysis with inductively coupled plasma time-of-flight mass spectrometry for the simultaneous determination of elements forming hydrides and its application to urine. J. Anal. At. Spectrom., 15, 1357. 

The remainder of the chapter discusses microdialysis coupled to mass spectrometric detection to both on-line and off-line methods, with an emphasis on analysis of drugs. Applications of microdialysis/mass spectrometry to gas chro-matography (GC), liquid chromatography (LC), and flow injection into the mass spectrometer are discussed. In particular, approaches to overcome problems with introduction of high-ionic-strength dialysate into the mass spectrometer are described. 

Microdialysis coupled to mass spectrometry is a powerful technique for on-and off-line analysis, providing information on pharmacokinetics, drug transport, and metabolite formation. With the widespread availability of LC/ESI/MS instruments there has been a shift toward liquid chromatography and away from gas chromatography and flow injection. Electrospray is the ionization method of choice for most applications and tandem mass spectrometry has grown in popularity. Thermospray and cfFAB applications have been used with microdialysis, but are older, obsolete techniques. 

FIA and, in particular, computer-controlled derived techniques still have an important contribution to make to quality control aspects in food analysis. Future trends will accompany the changes observed in analytical laboratories, where mass spectrometry-based detectors are replacing molecular spectrophotometry (e.g., diode array detectors [DAD]). Hence, it is expected the hyphenation of flow injection techniques to mass spectrometry, particularly for sample treatment (extraction, sample matrix removal) using FIA. Other less exploited feature, designated as reversed FIA (Mansour and Danielson, 2012), may also have an important role in future years. In this case, sample is applied as carrier, which allows an enhancement of detection limits. The only constraints are possible sample scarcity or high cost and multiplication of artifacts due to interferences. The future application of FIA is left to the imagination and ingenuity of future food analysts. 

Bings N. H., Steeanka Z. and Mallada S. R. (2003) Flow injection electrochemical hydride generation inductively coupled plasma time-of flight mass spectrometry for the simultaneous determination of hydride-forming elements and its application to the analysis of fresh water samples. Anal. Chim. Acta 479 203-214. 

Eaton, A. N., Hutton, R. C., and Holland, J. G. (1992). Application of flow injection sample introduction to inductively coupled plasma-mass spectrometry for geochemical analysis. Chem. Ceol. 95(1-2), 63-72. 

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