5. When using the CHIRALPAK® immobilised columns, are there any problems with diluting my sample in a solvent other than mobile phase?
Generally, the best procedure is to dissolve a sample in mobile phase, whenever possible. Care must still be taken when injecting sample dissolved in a solvent that has greater solvating power than mobile phase. This is a general chromatographic problem in that this may cause distortion of the chromatographic peaks, thus affecting the analytical results. In preparative chromatography there is a risk that sample from a concentrated injection in a good solvent will precipitate on the column, once the sample comes in contact with a mobile phase in which it has poorer solubility. An additional problem could occur if the column has greater attraction for sample diluent than for mobile phase. In such cases, sample diluent may stick to the column and affect the selectivity or efficiency of future injections.
For some applications, samples are presented in dichloromethane (DCM) or DCM mixtures. Other solvents, such as DMSO or DMF, are also allowed for sample injection but they may produce more perturbance in the front end separation. Precipitation issues may also be encountered.
Of course, since the stationary phase is immobilised, there are no issues with stability of the column under any of the above circumstances. However, frit clogging could be an issue.