Multidimensional chromatograph

MULTIDIMENSIONAL CHROMATOGRAPHIC METHODS WHICH INVOLVE THE USE OF SUPERCRITICAL FLUIDS... 

In order to reduce or eliminate off-line sample preparation, multidimensional chromatographic techniques have been employed in these difficult analyses. LC-GC has been employed in numerous applications that involve the analysis of poisonous compounds or metabolites from biological matrices such as fats and tissues, while GC-GC has been employed for complex samples, such as arson propellants and for samples in which special selectivity, such as chiral recognition, is required. Other techniques include on-line sample preparation methods, such as supercritical fluid extraction (SFE)-GC and LC-GC-GC. In many of these applications, the chromatographic method is coupled to mass spectrometry or another spectrometiic detector for final confirmation of the analyte identity, as required by many courts of law. 

Figure 15.6 Chromatogram of a plasma standard of human leukocyte elastase inhibitors obtained by using LC-LC. Adapted from Journal of Liquid Chromatography and Related Technologies, 19, R. A. Earley and L. R Tini, Versatile multidimensional chromatographic system for di ug discovery as exemplified by the analysis of a non-peptidic inhibitor of human leukocyte elastase , pp. 2527-2540, 1996, by courtesy of Marcel DekkeiTnc.

N. P. J. Price and R. W. Carlson, Rhizobial lipo-oligosaccharide nodulation factors multidimensional chromatographic analysis of. symbiotic signals involved in the development of legume root nodules, Glycobiology 5 233 (1995). 

Figure 8.17 Conversion of a standard gas chromatograph to a dual capillary column multidimensional chromatograph using a commercially available conversion kit. (Reproduced with permission from Scientific Glass Engineering). ...

A number of conversion kits are now commercially available that enable any single- or two-oven gas chromatograph to be converted into a multidimensional chromatograph, for example. Figure 8.17 [200,217-219]. To simplify installation all the... 

HPLC as a purification technique and as a tool for process monitoring has become increasingly attractive and will find many new applications in the future. Low pressure LC, probe LC, and micro-LC are techniques important to the future of process chromatography. Specialized detectors and multidimensional chromatographic approaches are also of increasing use. Additional literature is available.22 33-36... 

Table 7.86 Main characteristics of single-column and multidimensional chromatographic systems...

Applications If an extract needs further cleanup, it is possible to couple it with multidimensional chromatographic techniques such as LC-LC or LC-GC. The first chromatographic step can then be used for the on-line cleanup and concentration of the extract, and the second one for the final separation. Large-volume, on-column injection (LVI-COC) is particularly useful for coupled LC-GC in which 100-350 xL fractions of eluent from the NPLC cleanup separation step are transferred on-line to the GC column. For example, on-line removal of high-MW interfering material, such as polymers from a polymer/additive dissolution, can be achieved easily by using SEC before the fraction containing additives is transferred to the GC. 

The literature reports various (multidimensional) chromatographic approaches involving SEC and LC operating on dissolved polymer/additive mixtures. Floyd [985] has used microbore (1 mm i.d.) SEC-RPLC for the quantitative analysis of Tinuvin P in a cellulose acetate solution in THF, after separation of the polymeric and additive fractions total analysis time about 30 min. Relative accuracy and precision of 3 % and 1.5% were quoted. SEC-RPLC was also used to determine the styrene level in polystyrene crystals [986]. Additives in copolymers have been separated in a SEC/C system [987]. Chlorohydrin mixtures may be analysed by RPLC, but not in the presence of polymer. Thus, SEC... 

Various techniques have been introduced which still lack specific applications in polymer/additive analysis, but which may reasonably be expected to lead to significant contributions in the future. Examples are LC-QToFMS, LC-multi-API-MS, GC-ToFMS, Raman spectroscopy (to a minor extent), etc. Expectations for DIP-ToFMS [132], PTV-GC-ToFMS [133] and ASE are high. The advantages of SFC [134,135], on-line multidimensional chromatographic techniques [136,137] and laser-based methods for polymer/additive analysis appear to be more distant. Table 10.33 lists some innovative polymer/additive analysis protocols. As in all endeavours, the introduction of new technology needs a champion. 

In general, a comprehensive separation strategy implies the desire to resolve/analyze all components within a sample. In the specific context of a multidimensional chromatographic method, the term is more narrowly applied to indicate that all analytes introduced to the first-dimension separation are also subjected to a second-dimension separation. There are two basic configurations used by our laboratory to carry out comprehensive multidimensional (IEX/RP) protein separations—IEX— Dual Column RP system and IEX—Dual Trap RP system (Figs. 13.1 and 13.2), respectively. 

Millea, K.M., Krull, I.S., Cohen, S.A., Gebler, J.C., Berger, S.J. (2006). Integration of multidimensional chromatographic protein separations with a combined top-down and bottom-up proteomic strategy. J. Proteome. Res. 5, 135-146. 

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