Liquid HPLC

Chemical separations may first be accomplished by partitioning on the basis of polarity into a series of solvents from non-polar hexane to very polar compounds like methanol. Compounds may also be separated by molecular size, charge, or adsorptive characteristics, etc. Various chromatography methods are utilized, including columns, thin layer (TLC) gas-liquid (GLC), and more recently, high pressure liquid (HPLC) systems. HPLC has proven particularly useful for separations of water soluble compounds from relatively crude plant extracts. Previously, the major effort toward compound identification involved chemical tests to detect specific functional groups, whereas characterization is now usually accomplished by using a... 

Gas (GC) and Liquid (HPLC) Chromatographs These are similar to spectrophotometers in that they are calibrated via a detector response to some property of analyte. The analyte may either be in solution or, in the case of GC (Figure 5.9), in pure form. Again, a calibration (or "standard") curve of detector response vs. either concentration or amount of pure chemical used is plotted and unknowns determined by correlation with the known stan-... 

There are few methods which can measure well-defined metal fractions with sufficient sensitivity for direct use with environmental samples (approach B in Fig. 8.2). Nevertheless, this approach is necessary in the experimental determination of the distribution of compounds that are labile with respect to the time scales of the analytical method. Recent literature indicates that high-performance liquid (HPLC) and gas chromatographic (GC) based techniques may have such capabilities (Batley and Low, 1989 Chau and Wong, 1989 van Loon and Barefoot, 1992 Kitazume et al, 1993 Rottmann and Heumann, 1994 Baxter and Freeh, 1995 Szpunar-Lobinska et al, 1995 Ellis and Roberts, 1997 Vogl and Heumann, 1998). The ability to vary both the stationary and mobile phases, in conjunction with suitable detector selection (e.g. ICP-MS), provides considerable discriminatory power. HPLC is the superior method GC has the disadvantage that species normally need to be derivatised to volatile forms prior to analysis. Capillary electrophoresis also shows promise as a metal speciation tool its main advantage is the absence of potential equilibria perturbation, interactions... 

Name Liquid-liquid (LLC) column (CC) High-pressure liquid (HPLC)... 

B. Gel Permeation and Normal-Phase Liquid-Liquid HPLC... 

A liquid (HPLC) or gas (GC) chromatograph usually consists of five essen-... 

Stilbenes and related compounds can be separated with a number of techniques such as thin-layer (TLC), gas liquid (GLC), and high-performance liquid (HPLC) chromatography (Gorham, 1989). The detection and identification of these compounds can best be accomplished by nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (Gorham, 1980 1989). 

Table 10 compares. some important physicochemical properties of a liquid (HPLC). a gas (GC). and a supercritical fluid. The density— and thus the solvation characteristics of the supercritical fluid — are very similar to those of a liquid. 

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