Development of a Direct Sampling Module for Compact Capillary Liquid Chromatography

The automation of reaction monitoring analysis can greatly improve the capability to obtain real-time feedback on reaction progress and aid in method optimization. Liquid chromatography (LC) is a widely used analytical technique for organic reaction monitoring, but the large size of the instrumentation can make online analysis difficult and impractical. Compact and miniaturized LC instrumentation provides the opportunity to simplify the process of analyzing samples at the reaction site, but the smaller scale of capillary LC columns is often incompatible with commercial reaction sampling systems designed to work with larger volumes. Here, a compact sampling module (CSM) designed to automate sample collection from a variety of reaction devices with volumes that are compatible with capillary LC is reported. The design and operation of the system are described, as well as example uses within a conventional medicinal chemistry setting. Specifically, the real-time analysis of both standard reactions in flow and batch settings with sampling performed by the CSM is described. Furthermore, the utility of the module in analyzing photoredox-based reactions, which are currently experiencing significant growth within drug discovery, is described. Performance of the system is compared to a traditional benchtop LC instrument that is currently used as the primary platform for standard reaction analysis, with a repeatability comparison between the systems demonstrating averages of 0.8%RSD (percentage relative standard deviation) for retention time and 2.5%RSD for peak area on the compact system and 1.4 and 9.4%RSD, respectively, for the benchtop system. The average observed carryover using the compact LC with CSM was also lower than the benchtop LC (0.3% and 1.5%, respectively), although detection limits were higher due to the shorter pathlength on-column ultraviolet-absorbance flow cell used in this work.