Hyphenated liquid chromatography

J. A. De Koning, A. C. Hogenboom, T. Lacker, S. Strhoschein, K. Albert, and U. A. Th. Brinkman, On-line trace enrichment in hyphenated liquid chromatography-nuclear magnetic resonance spectroscopy,/. Chromatogr. A 813 (1998), 55-61. 

Yang Z. Online hyphenated liquid chromatography-nuclear magnetic resonance spectroscopy-mass spectrometry for drug metabolite and nature product analysis. J Pharm Biomed Anal 2006 40 516-527. 

This is a relatively recent addition to the ionisation techniques used with hyphenated liquid chromatography. In this type of detector, a vaporiser converts the eluent (from the LC) into the gas phase, much like with APCI. The difference with this technique is that instead of the production of electrons from a corona, here we have a discharge lamp producing photons (known as vacuum ultraviolet photons) in a narrow range of ionisation energies. 

De Koning, J.A. Hogenboom, A.C. Lacker, T. Strhoschein, S. Albert, K. Brinkman, U.A.Th. On-hne trace enrichment in hyphenated liquid chromatography-nuclear magnetic resonance spectroscopy. J. Chromatogr. A, 1998,813,55-61. 

Coulier, L., Kaal, E.R., Hankemeier, T. (2005) Comprehensive two-dimensional liquid chromatography and hyphenated liquid chromatography to study the degradation of poly (bisphenol A) carbonate. J. Chromat. A, 1070, 79-87. 

Guan, F., Uboh, C.E., Soma, L.R., et al. (2004) Confirmation and quantification of hemogiobin-based oxygen carriers in equine and human plasma by hyphenated liquid chromatography tandem mass spectrometry. Analytical Chemistry, 76,5127-5135. 

Strohschein, S., Pursch, M., and Albert, K., Hyphenation of high performance liquid chromatography with nuclear magnetic resonance spectroscopy for the characterization of (3-carotene isomers employing a Cjq stationary phase, J. Pharm. Biom. Anal., 21, 669, 1999. 

The spectrum of new analytical techniques includes superior separation techniques and sophisticated detection methods. Most of the novel instruments are hyphenated, where the separation and detection elements are combined, allowing efficient use of materials sometimes available only in minute quantities. The hyphenated techniques also significantly increase the information content of the analysis. Recent developments in separation sciences are directed towards micro-analytical techniques, including capillary gas chromatography, microbore high performance liquid chromatography, and capillary electrophoresis. 

Gas and liquid chromatography directly coupled with atomic spectrometry have been reviewed [178,179], as well as the determination of trace elements by chromatographic methods employing atomic plasma emission spectrometric detection [180]. Sutton et al. [181] have reviewed the use and applications of ICP-MS as a chromatographic and capillary electrophoretic detector, whereas Niessen [182] has briefly reviewed the applications of mass spectrometry to hyphenated techniques. 

Wilson [664,672] has reviewed multiple hyphenation of liquid chromatography. 

Because carotenoids are light- and oxygen-sensitive, a closed-loop hyphenated technique such as the on-line coupling of high performance liquid chromatography (HPLC) together with nuclear magnetic resonance (NMR) spectroscopy can be used for the artifact-free structural determination of the different isomers. 

Putzbach, K., Krucker, M., Grynbaum, M. D., Hentschel, P., Webb, A. G., and Albert, K. 2005. Hyphenation of capillary high-performance liquid chromatography to microcoil magnetic resonance spectroscopy—Determination of various carotenoids in a small-sized spinach sample. J. Pharm. Biomed Anal. 38 910-917. 

Jia, L., Liu, B., Terabe, S., Nishioka, T. (2004). Two-dimensional separation method for analysis of bacillus subtilis metabolites via hyphenation of micro-liquid chromatography and capillary electrophoresis. Anal. Chem. 76, 1419-1428. 

Cheguillaume, G., Buchmann, W., Desmazieres, B., Tortajada, J. (2004). Liquid chromatography-mass spectrometry hyphenation for exhaustive and unambiguous characterization of polyoxyethylene surfactants. Chromatographia 60(9/10), 561-566. 

Pasch, H. Analysis of Complex Polymers by Interaction Chromatography. Vol. 128, pp. 1 -46. Pasch, if. Hyphenated Techniques in Liquid Chromatography of Polymers. Vol. 150,... 

Wilson ID. 2000. Multiple hyphenation of liquid chromatography with nuclear magnetic resonance spectroscopy, mass spectrometry and beyond. J Chromatogr A 892 315-327. 

Chromatographic methods are also often used as part of systems that are called hyphenated methods, (see Chapter 15) where the output of the chromatographic section is used as the input for an identification method such as mass spectrometry. These hyphenated methods are also most often referred to by their acronyms, for example, GC-MS—gas chromatography-mass spectrometry and HPLC-MS—high-performance liquid chromatography-mass spectrometry. Note that although ultraviolet-visible (UV-Vis) is hyphenated, it is not a hyphenated method in that it does not consist of two different methods of analysis. Hyphenated methods will be discussed fully in Chapter 15. 

Sample preparation for analysis by hyphenated methods requires some additional planning when compared to nonhyphenated methods. All steps, extraction, concentration, and final solvent selection must take into consideration and be compatible with all the components of the hyphenated instrumentation. For gas chromatographic methods, all the components in the mixture must be in the gaseous state. For liquid chromatography (LC) or high-performance liquid chromatography (HPLC), the samples of the analytes of interest can be solids or liquids, neutral or charged molecules, or ions, but they must be in solution. If the follow-on analysis is by MS, then each of the analytes may require a different method of introduction into the MS. Metals and metal ions may be introduced by HPLC if they are in solution but commonly are introduced via AAS or inductively coupled plasma (ICP). Other analytes may be directly introduced from HPLC to MS [2],... 

In the last twenty years, many of the developed and validated high performance liquid chromatography methods with conventional diode array or fluorescence detectors (DAD, FLD) were improved and substituted by new hyphenation with mass spectrometric instrumentation and/or NMR, especially for the analyses of raw materials derived from Natural sources. The main goal of this coupling is achieved by improvement of selectivity and sensitivity of new instrumental configurations [7], Furthermore, with these configurations it is possible to obtain, in only one analysis, the complete chemical structure elucidation, identification and quantification of targeted compounds. 

As liquid chromatography plays a dominant role in chemical separations, advancements in the field of LC-NMR and the availability of commercial LC-NMR instrumentation in several formats has contributed to the widespread acceptance of hyphenated NMR techniques. The different methods for sampling and data acquisition, as well as selected applications will be discussed in this section. LC-NMR has found a wide range of applications including structure elucidation of natural products, studies of drug metabolism, transformation of environmental contaminants, structure determination of pharmaceutical impurities, and analysis of biofiuids such as urine and blood plasma. Readers interested in an in-depth treatment of this topic are referred to the recent book on this subject [25]. 

Hyphenated analytical techniques such as LC-MS, which combines liquid chromatography and mass spectrometry, are well-developed laboratory tools that are widely used in the pharmaceutical industry. Eor some compounds, mass spectrometry alone is insufficient for complete structural elucidation of unknown compounds nuclear magnetic resonance spectroscopy (NMR) can help elucidate the structure of these compounds (see Chapter 20). Traditionally, NMR experiments are performed on more or less pure samples, in which the signals of a single component dominate. Therefore, the structural analysis of individual components of complex mixtures is normally time-consuming and less cost-effective. The... 

---