Quantitation of combinatorial libraries of small organic molecules by normal-phase HPLC with evaporative light-scattering detection

The advantages of evaporative light-scattering detection over UV detection for the quantitation of combinatorial libraries composed of small organic compounds by HPLC are described. The detector's response is independent of the sample chromophore, which makes it well-suited to chromatographic analyses of mixtures of dissimilar solutes. Thus, HPLC with evaporative light-scattering detection offers the potential for reducing false positive or false negative results in screening assays, because of its ability to detect the presence of impurities that absorb poorly in the UV (e.g., those impurities originating from the polymeric support). Furthermore, the evaporative light-scattering detector exhibits a nearly equivalent response to compounds of similar structural class. Hence, rapid quantitation of compound libraries may be carried out with the use of a single external standard. For example, the quantitation errors, based on a single external standard, for a series of steroids, hydantoins, and BOC- and Fmoc-protected amino acids by normal-phase HPLC with evaporative light-scattering detection average approximately +/- 10%. The application of the evaporative light-scattering detector to the quantitation of low-level sample impurities and the detector's compatibility with gradient elution are also described.