Chromatography hyphenated systems

Analytical methods based on high-performance liquid chromatography, hyphenated with different detection systems are the methods of election to study the multiform aspects of environmental analysis. 

To obtain a comprehensive analysis of carbohydrate mixtures from biological matrices that display a high degree of compositional and structural heterogeneity, a multidimensional approach is required. The combination into a so-called hyphenated system, of liquid chromatography (LC) or CE with MS provides the advantage of selective and efficient separation with the mass specificity, sensitivity, and structural information gained from MS. 

The problem of cross-talk between several microcoils has been solved by Professor Andrew Webb and his coworkers, but application in parallel HP LC-NMR detection has stiU yet to be achieved. For this, adequate NMR instrumentation will be necessary. Parallel HPLC-NMR detection with four microcoils in a hyphenated system will surely be realized within the next few years, and in the longer term a configuration of 16 microcoils in four parallel horizontal detection planes, as introduced by Professor Raftery, will be realized. Besides parallel detection, the capillary technique in principle opens the door for the hyphenation of NMR spectroscopy with other capillary separation techniques such as gas chromatography and supercritical fluid chromatography (SFC). The long spin-lattice relaxation times in the supercritical and gaseous states can be reduced by relaxation agents present in the separation capillary prior to the actual NMR detection. 

The role of laboratory GC will decrease in favour of on-line GC. Self diagnostic fault finding and advanced calibration/validation will develop and more extensive use of multidimensional and hyphenated systems will be made. Microtechnology in process gas chromatography was recently illustrated [263]. Table 7.33 summarises the vision for PGC 2000+. 

The possibiHties for multidimensional iastmmental techniques are endless, and many other candidate components for iaclusion as hyphenated methods are expected to surface as the technology of interfacing is resolved. In addition, ternary systems, such as gas chromatography-mass spectrometry-iafrared spectrometry (gc/ms/ir), are also commercially available. 

Coupling of analytical techniques (detectors) to high-performance liquid chromatographic (HPLC) systems has increased in the last tree decades. Initially, gas chromatography was coupled to mass spectrometry (MS), then to infrai ed (IR) spectroscopy. Following the main interest was to hyphenate analytical techniques to HPLC. 

Applications In most polymer/additive analysis applications, a QMS is applied in view of its ease of use, relatively low cost, and coupling with chromatography (Section 7.3). The ability of QMS to cope with large solvent volumes flowing into the ionisation source for extended periods of time and ease of interfacing - both to computers and chromatographs - makes it the choice for multi-user systems, and has facilitated hyphenation with GC, LC and TG. Consequently, QMS are a mainstay of GC-MS, LC-MS and TG-MS. 

If total analysis systems are not exactly the best option for polymer/additive analysis, then neither are chip-based hyphenations. The reasons here are completely different minute sample size (homogeneity problems for more traditional samples), and (theoretical) limits to chromatography and concentration-based sensitivity, etc. 

---