Liquid Chromatography/Infrared Spectroscopy
Published Online: 15 SEP 2006
Copyright © 2000 John Wiley & Sons, Ltd. All rights reserved.
Encyclopedia of Analytical Chemistry
How to Cite
Somsen, G. W. and Visser, T. 2006. Liquid Chromatography/Infrared Spectroscopy. Encyclopedia of Analytical Chemistry. .
- Published Online: 15 SEP 2006
Analytical techniques that combine liquid chromatography (LC) and infrared (IR) spectroscopy have been developed primarily to permit specific detection and/or identification of sample constituents. LC is an important and extensively used method for the separation of mixtures into their individual components. IR spectroscopy is very useful for the characterization of functional groups and has strong compound-identification capabilities which are especially suited for the differentiation of structural isomers. Over the past years the coupling of LC and IR spectroscopy (LC/IR) has been accomplished by two different approaches. The first and simplest approach is to use a flow cell through which the effluent from the LC column is passed while the IR spectra are continuously measured. The merits of flow-cell IR detection include ease of operation, real-time detection and low maintenance, but its main disadvantage lies in the significant IR-absorption of the solvents commonly used in LC. These absorptions seriously limit both the detection sensitivity and the obtainable spectral information. The second approach involves elimination of the LC solvent prior to IR detection. In this approach an interface is used to evaporate the eluent and deposit the separated compounds onto a substrate suitable for IR detection. The primary advantages of solvent-elimination LC/IR are the possibility to obtain full spectra of the analytes and the considerably enhanced sensitivity when compared to flow-cell detection. Unfortunately, common LC solvents, and particularly aqueous eluents, are not easily removed and therefore the evaporation interfaces are often rather complex. This article reviews the developments, practical aspects, applications and current status of LC/IR, covering both coupling approaches. It follows that despite the unfavorable detection limits, flow-cell LC/IR can be useful for the specific and quantitative detection of major components of mixtures. However, solvent-elimination-based IR-detection should be used when small amounts of sample constituents have to be characterized with a high level of confidence. In general, the practical use of IR detection in LC is still limited, but the advent of various (commercial) flow-cell and interface designs shows that LC/IR is more and more being recognized as a feasible and rewarding technique.