Liquid chromatography combined techniques

Explores strategies for optimizing techniques such as high-performance liquid chromatography combined with mass spectrometry (HPLC-MS) or tandem mass spectrometry (HPLC-MS-MS)... 

CG Rimkus, M Rummler, I Nausch. Gel permeation chromatography high-performance liquid chromatography combination as an automated clean-up technique for the multiresidue analysis of fats. J Chromatogr A 737 9-14, 1996. 

Over the past decade, liquid chromatography combined with mass spectrometry (LC/MS) has evolved from being primarily a research tool, available in a limited number of analytical laboratories, to a robust and widely available analytical and investigative technique (1 3). It is now in widespread use in pharmaceutical, food, environmental, and forensic laboratories and is an indispensable tool in biomedical research. At the time of our previous review of this subject (4), few laboratories were using LC/MS in the analysis of chemicals relevant to the Chemical Weapons Convention (CWC). This was due to a number of factors, two of which were the cost of instrumentation and a perception that the technique was difficult to implement in an analytical laboratory. In the intervening years, the costs of basic LC/MS have been reduced, and the instrumentation has become robust and easier to operate. LC/MS is now a mature technique that should be considered by all laboratories that are required to analyze chemicals related to the CWC. 

Liquid chromatography combined with tandem mass spectrometry (LC-MS/MS) is the analytical technique of choice for measurement of ionic PFCs in environmental samples. Recent reviews on the use of this technique for the analysis of PFCs have been published by de Voogt and Saez [111] and Villigrasa, Lopez de Alda and Barcelo [96]. 

Furthermore, the voltammetric data established a background for the quantitative determination of catecholamines using a selective am-perometric detector in combination with liquid chromatography (LCEC technique) 254). The tendency of this class of compounds to absorb at electrode surfaces (such as platinum) allowed the determination of... 

Of the many analytical techniques now available to the lipid chemist, mass spectrometry (MS), is probably the one that has experienced the fastest growth in the last two decades. This is due both to the development of new techniques (gas and liquid chromatography combined with MS, soft-ionization MS, field desorption MS, atmospheric pressure MS etc.) and to the refinement of more traditional methods and their successful application to very complex problems, e.g. the elucidation of glycolipid structure, or the study of structures in lipid mixtures. Much progress has been made since the pioneering work of Ryhage and Stenhagen (1963) on fatty acid methyl esters. 

Adsorption chromatography is one of the more popular modern high-performance liquid chromatography (HPLC) techniques today. However, open-column chromatography and TLC are still widely used. - The adsorbents (stationary phases) used are silica, alumina, and carbon. Although some bonded phases have been considered to come under adsorption chromatography, these bonded phases will not be discussed. By far, silica and alumina are more widely used than carbon. The mobile phases employed are less polar than the stationary phases, and they usually consist of a signal or binary solvent system. However, ternary and quaternary solvent combinations have been used. 

Capillary electrochromatography, CEC, is a relatively new technique, and is a hybrid of capillary electrophoresis and high-performance liquid chromatography, combining elements of both. Particular features of CEC are ... 

Liquid chromatography/mass spectrometry (LC/MS) is an analytical technique combining the advantages of an LC instrument with those of a mass spectrometer. 

LC/MS. liquid chromatography and mass spectrometry used as a combined technique... 

In the first chapter, I have discussed the limitations of high performance liquid chromatography (HPLC) and mass spectrometry when used in isolation and how the combination of the two allows these to be overcome. In this chapter, the effect of combining the two techniques with regard to the individual performance characteristics are explored. 

The characteristics of an ideal liquid chromatography-mass spectrometry interface have been discussed, with emphasis having been placed upon the major incompatibilities of the two component techniques that need to be overcome to allow the combination to function effectively. 

There are a number of specialist texts in which high performance liquid chromatography (HPLC) is described in varying amounts of detail (Lindsay [2] Robards et al. [3] Meyer [4]). It is not, therefore, the intention of this author to provide a comprehensive description of the technique but merely to discuss those aspects which are essential to the successful apphcation of the LC-MS combination. 

The need for a more definitive identification of HPLC eluates than that provided by retention times alone has been discussed previously, as have the incompatibilities between the operating characteristics of liquid chromatography and mass spectrometry. The combination of the two techniques was originally achieved by the physical isolation of fractions as they eluted from an HPLC column, followed by the removal of the mobile phase, usually by evaporation, and transfer of the analyte(s) into the mass spectrometer by using an appropriate probe. 

Because of this lack of resolving power, much electroanalytical research is aimed at providing increased selectivity. This can be accomplished in two ways. First, electrochemistry can be combined with another technique which provides the selectivity. Examples of this approach are liquid chromatography with electrochemical detection (LCEC) and electrochemical enzyme immunoassay (EEIA). The other approach is to modify the electrochemical reaction at the electrode to enhance selectivity. This... 

---