High resolution separation column Initiation

High- performance liquid chromatography High resolution, different columns are available to separate polysaccharides with different properties Need initial fractionation (purification) by GFC or anion exchange methods [99-101]... 

Separation of PAHs with GC has been on since the late 1950s. Initially all were performed with packed columns, but in the recent past high-resolution capillary columns are also being employed. Most separations nowadays are made on cross-linked fused silica capillary columns, often with nonpolar or slightly polar phases. High column efficiency, which is possible with GC columns, enables the determination of large number of PAHs and to separate some critical pairs and isomers of certain PAHs. The capillary efficiency of GC can be as high as 70,000 HETP (theoretical plate) [7]. 

GC on a fused silica capillary column with an MS detector should be used whenever possible for the analysis of organic compounds at trace level in complex mixtures. In fact, it allows the extremely high resolution of GC to be combined with the very high sensitivity and identification power of MS, which makes it possible to determine an analyte at low pg mC levels in the final organic extract. However, GC-ECD is very common for PCB determination since it is both the most sensitive and the less expensive technique for chlorinated compounds (5). PCBs can be separated on a 30-50 m fused silica capillary column with 5% phenyl -95% methylpolysiloxane chemically bonded stationary phase (1). On-column injection is very often used, while several oven temperature programmes have been applied for PCB determinations. The initial temperature is generally 10-15°C lower than the boiling point of the solvent and the final one does not exceed 290-300°C. 

Silica-base stationary phases have also been employed for enantiomeric separations in CEC [6,72-81]. In the initial work on chiral CEC, commercially available HPLC materials were utilized, including cyclodextrins [6,74,81] and protein-type selectors [73,75,80] such as human serum albumin [75] and ai-acid glycoprotein [73]. Fig. 4.9, for example, depicts the structure of a cyclodextrin-base stationary phase used in CEC and the separation of mephobarbital enantiomers by capillary LC and CEC in a capillary column packed with such a phase. The column operated in the CEC mode affords higher separation efficiency than in the capillary LC mode. Other enantiomeric selectors are also use in CEC, including the silica-linked or silica-coated macrocyclic antibiotics vancomycin [82,83] and teicoplanin [84], cyclodextrin-base polymer coated silicas [72,78], and weak anion-exchage type chiral phases [85]. Relatively high separation efficiency and excellent resolution for a variety of compounds have also been achieved using columns packed with naproxen-derived and Whelk-0 chiral stationary phases linked to 3 pm silica particles [79]. Fig. 4.10 shows the... 

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