High performance liquid chromatography hyphenated techniques

Keywords Crystallization analysis fractionation Field Flow Fractionation High performance liquid chromatography Hyphenated techniques Liquid chromatography Polyolefin analysis SEC-NMR coupling Size exclusion chromatography Temperature rising elution fractionation Two-dimensional liquid chromatography... 

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. 

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. 

Lustig, S., Michalke, B., Beck, W. and Schramel, R (1998) Platinum speciation with hyphenated techniques high performance liquid chromatography and capillary electrophoresis on-line coupled to an inductively coupled plasma mass spectrometer -application to aqueous extracts from a platinum treated soil. Fresenius J. Anal. Chem., 360,18-23. 

Korhammer SA, Bernruether A, Hyphenation of high-performance liquid chromatography (HPLC) and other chromatographic techniques (SFC, GPC, GC, CE) with nuclear magnetic resonance (NMR) A review, J. Anal. Chem., 354 131-135, 1996. 

The resolution of a multicomponent system involves the description of the variation of measurements as an additive model of the contributions of their pure constituents [1-10]. To do so, relevant and sufficiently informative experimental data are needed. These data can be obtained by analyzing a sample with a hyphenated technique (e.g., HPLC-DAD [diode array detection], high-performance liquid chromatography-DAD) or by monitoring a process in a multivariate fashion. In these and similar examples, all of the measurements performed can be organized in a table or data matrix where one direction (the elution or the process direction) is related to the compositional variation of the system, and the other direction refers to the variation in the response collected. The existence of these two directions of variation helps to differentiate among components (Figure 11.1). 

Cyclodextrins were used for the modification of such chromatographic techniques as gas chromatography, classical liquid chromatography, high performance liquid chromatography, thin layer chromatography and many hyphenated techniques. Since in the study of enantiomeric composition of monoterpenes gas chromatography modified with cyclodextrins is the main analytical tool, this method will be more widely discussed later on. 

As ESI works on a continuous flow of liquid, it has quickly been coupled to LC or other liquid-phase separation techniques as an alternative to optical detection.15 Mass spectrometry gives more information on the eluted compound, and the resulting hyphenated technique enables one to decrease the complexity of samples before their analysis by MS. High performance liquid chromatography (HPLC) is coupled to conventional ESI-MS while nanoLC is connected to nanoESI-MS for a better match in the flow-rate values. 

Mixtures can be identified with the help of computer software that subtracts the spectra of pure compounds from that of the sample. For complex mixtures, fractionation may be needed as part of the analysis. Commercial instruments are available that combine ftir, as a detector, with a separation technique such as gas chromatography (gc), high performance liquid chromatography (hplc), or supercritical fluid chromatography (96,97). Instruments such as gc/ftir are often termed hyphenated instruments (98). Pyrolyzer (99) and thermogravimetric analysis (tga) instrumentation can also be combined with ftir for monitoring pyrolysis and oxidation processes (100) (see Analytical methods, hyphenated instruments). 

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