Column Testing Stability and Selectivity

The final part of the chapter provides a refresher on pA from an analytical chemist s perspective, the drivers for choosing normal phase versus reversed phase as a separation mode for a particular analysis, and instru-ment/system consideration, and it concludes with a very interesting section on column testing within the framework of bonded phase stability (effect of pH and type of buffer) and probing column selectivity. 

A column performance test is used to ensure the proper condition of columns and the stability of retention parameters. Because CWC-related chemicals greatly differ both chemically and physically from each other, the test chemicals have been selected so that their physical, chemical, and retention properties are different, and so that they elute evenly over the whole chromatogram. The use of the following chemicals in a column performance test is recommended trimethylphosphate, 2,6-dimethylphenol, 5-chloro-2-methylaniline, tri-n-butylphosphate, dibenzothiophene, malathion, and methyl stearate. The concentration of test chemicals depends on the sensitivity of detectors. The... 

Columns for a particular laboratory can be chosen based on some set of internal criteria. One of the criteria to select a column should be such that the column is stable for a certain number of column volumes (efficiency, tailing factor, and retention time criteria for predefined probe analytes) at the recommended maximum and minimum pH at a particular maximum temperature. This would allow the chromatographer to employ such phases with a significant degree of confidence and ensure the robustness of the stationary phase during method development and for release and stability testing. 

A continuous-flow method for asymmetric catalysis in an SCF/IL system was reported by Leitner s group (144), with the hydrovinylation of styrene [Eq. (31)] as the test reaction. The SCCO2 solution of styrene and ethylene was continuously bubbled up through a column of ionic liquid containing the catalyst. The enantio selectivity was found to be high (in one of the ILs) and catalyst stability was enhanced due to the fact that there was a constant concentration of substrate in the system the catalyst was unstable in ILs in the absence of the olefins. 

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