How Reliable Are Enantiomeric Excess Measurements Obtained By Chiral HPLC?

Uncertainties and errors in enantiomeric excess determinations obtained by high performance liquid chromatography (HPLC) with a chiral column are evaluated with different peak resolutions and elution orders using (R)- and (S)-ibuprofen standards. Five injections of each sample were made to reduce the variability in the data and each chromatogram was monitored at multiple wavelengths to facilitate the detection of chemical impurities. Using appropriate sample concentrations, the most favorable detection wavelengths, and default instrument parameters led to large errors (>10 %) whereas properly set integration values gave impressive reproducibilities (±0.5 % or better) and accuracies (<1 %) in the most favorable situations. Uncertainties and errors of up to±2.0 % and 5.2 % ee, respectively were also observed under separation conditions routinely reported in chemistry journals. This study aims to provide a practical guide to the accuracy and precision that can be achieved with HPLC, and suggestions for obtaining reliable results.