Real-time assessment of enantiomeric purity via a polarimetric/absorption detector response function.

The development of methodology appropriate for the rapid and precise assessment of enantiomeric purity is a critical need in the life sciences with impact in a number of areas including biomedical research, biotechnology, and pharmaceutical science. Real-time assessment of enantiomeric purity is critical to decisions related to possible product purity and/or the need for, and the type of additional processing. Recently, we have shown that laser-based polarimetric detection, in combination with ultraviolet detection, can be used to assess enantiomeric purity in real-time as an adjunct to the separation process. A mass-independent response function is obtained from the ratio of the normalized polarimetric signal relative to the normalized UV signal. This response ratio will be shown to be equivalent to the enantiomeric excess and independent of concentration and chromatographic resolution. The methodology will be evaluated as a function of injected mass, enantiomeric excess, chromatographic resolution, and peak asymmetry.

Quantitative analysis of incomplete HPLC resolution of enantiomers. Fit of polarimetric detection for D- and L-phenylalanine to a gaussian function.

This report compares laser-based polarimetric and UV data for quantitating incompletely resolved enantiomers by HPLC. Using L- and D-phenylalanine as a working model, response data is shown across the entire detection region while emphasizing the regions at or near 100% L, 100% D and 50:50 L:D at resolutions between 0.4 and 1.4. In general, the poorer the resolution, the greater the improvement in detectability with the polarimeter when compared to UV detection. This is due to the inherent bipolar nature of the polarimetric signal, which creates a well-defined crossing point for integration of an enantiomeric pair. In our previous work, we described the improvement in measurement precision when applying a bipolar gaussian peak model to the raw chromatographic peak data. This study will measure the model's effect on improving accuracy. This study should be applicable to other chiroptical detection strategies that produce a bipolar signal for enantiomers, such as circular dichroism and circularly polarized luminescence.