Separation of chiral pollutants

The separation of the isomers of some environmental pollutants (chlor-danes, toxaphenes etc.) is a challenging job, while the chiral resolution of these pollutants is extremely difficult. A multidimensional gas chromatographic (MDcGC) approach for such types of chiral resolution of environmental pollutants has been proposed as the best choice. The MDcGC technique involves the use of two chiral columns of different polarities in series, each with a separate temperature control. The remarkable advantage of this technique, in both a qualitative and a quantitative sense, is a consequence of the fact that a valveless pneumatic system, which involves a live T-piece, allows a preselected small fraction to be cut from the eluate of the first column and transferred quantitatively and reproducibly to the second column. This technique may be used for the complete separation of chiral pollutants, with increased sensitivity and selectivity. Examples of this technique for the chiral resolution of environmental pollutants can be found in several publications [93-96, 122, 123]. 

Capillary electrophoresis has been used for the analysis of chiral pollutants, e.g., pesticides, polynuclear-aromatic hydrocarbons, amines, carbonyl compounds, surfactants, dyes, and other toxic compounds. Moreover, CE has also been utilized to separate the structural isomers of various... 

Analysis of chiral pollutants by capillary electrophoresis (CE) is a new trend in separation science. This entry describes separation and identification of chiral xenobiotics by using CE. Attempts have been made to describe types of chiral selectors, applications, optimization of separations, detection strategies, mechanisms of chiral separations, CE vs chromatography and sample preparation methods. 

CE has been used for the analysis of chiral pollutants, e.g., pesticides, polynuclear aromatic hydrocarbons, amines, carbonyl compounds, surfactants, dyes, and other toxic compounds. Moreover, CE has also been utilized to separate the structural isomers of various toxic pollutants such as phenols, polyaromatic hydrocarbons, and so on. Sarac, Chankvetadze, and Blaschke " resolved the enantiomers of 2-hydrazino-2-methyl-3-(3,4-dihydroxyphenyl)propanoic acid using CD as the BGE additive. The CDs used were native, neutral, and ionic in nature with phosphate buffer as BGE. Welseloh, Wolf, and Konig investigated the CE method for the separation of biphenyls, using a phosphate buffer as BGE with CD as the chiral additive. Miura et al., used CE for the chiral resolution of seven phenoxy acid herbicides using methylated CDs as the BGE additives. Furthermore, the same group resolved 2-(4-chlorophenoxy) propionic acid (MCPP), 2-(2,4-dichlorophenoxy) propionic acid (DCPP), (2,4-dichlorophenoxy) acetic acid (2,4-D), 2-(4-chlorophenoxy) propionic acid (2,4-CPPA), [(2,4,5-... 

As discussed above, only a few reports are available on the chiral analysis of environmental pollutants and, therefore, HPLC still cannot achieve the status of a routine analytical technique in this field of work. Of course, HPLC has considerable potential in the field of chiral separation of environmental pollutants, due to the great merit of the technique, as already discussed. As discussed above, the different classes of CSPs can be used with a... 

Table 9.3 Commonly used buffers with suitable pHs and wavelengths for the chiral separation of environmental pollutants in CE [50]...

Various approaches to chiral resolution have been developed for the analysis of pharmaceuticals and drugs but, unfortunately, few reports and monographs are available on the chiral separation of pollutants. Therefore, we have set out to write this book, which deals with the distribution, toxicities and art of analysis of chiral pollutants by gas chromatography and liquid chromatography that is, by high performance liquid chromatography (HPLC), sub- and supercritical fluid chromatography (SFC),... 

The chiral resolution of environmental pollutants by CE is a very interesting feature, since one of the chiral isomers may be more toxic than the other. In addition, biological transformation of the enantiomers is many times stereoselective, and, therefore, their uptake, metabolism, and excretion can be different. Besides, CE has also been utilized to separate the structural isomers of various toxic pollutants such as phenols, polyaromatic hydrocarbons, etc. 

The introduction of capillary columns for GC analysis produced a breakthrough in the analysis of environmental pollutants due to their high separation efficiency. For environmental applications, fused-silica wall-coated open-tubular columns with internal diameters from 0.1 to 0.32 mm and film thickness of 0.1-0.2 pm, and lengths from 25 to 60 m are currently used. The wide range of stationary phases commercially available with different polarities and high thermal stabiHty provides the tool required to maintain the prominent position of GC in environmental analysis. In addition, the availability of chiral stationary phases gives GC the capability to perform GC enantiomer separations. Table 1 gives the recommended columns used in routine analysis of some selected pollutants. 

---