9. Are there any different mobile phase modifiers or additives for the CHIRALPAK® immobilised columns?
It is important to point out that the conditions described in Table 1 and Table 2 for HPLC in normal phase conditions are suitable for neutral compounds. For basic and acidic samples, it may be necessary to incorporate an additive in the mobile phase in order to allow the recognition and optimize the separation. Thus, basic samples may require a basic additive (DEA, butylamine, ethanolamine, ethylenediamine…) and acidic compounds the addition of an acid (TFA, acetic or formic acid…). The percentage needed is typically 0.1% and should normally not exceed 0.5%. In SFC this amount is also respected, although as added in the co-solvent it maybe 0.5 1%, but keeping the overall concentration in the final mobile phase. In RP-conditions, buffers will be used as included in the corresponding section.
It has been found that certain amines, such as EDA (ethylenediamine) and 2 aminoethanol (AE) induce much better behaviour for certain compounds than the more commonly used DEA. Resolution degree and peak symmetry can be dramatically improved with this type of additives. For practical purposes, as EDA and AE are often not miscible in the absence of alcohol, it is better running screenings with DEA, but it will be important in the optimization step to consider this fact. However, due to their limited miscibility with certain non-polar solvents, they are only recommended when at least 2% of ethanol or methanol are present in the mobile phase.