A Supercritical Fluid Chromatographic Method for the Determination and Separation of Boronic Acids

A green and high-throughput chromatography method was developed for the separation and quantification of boronic acids using an environmentally friendly supercritical fluid chromatography (SFC). The developed method was successfully applied for the separation of a mixture of five boronic acid compounds having different functional groups and also used for the quantification of over 15 wide ranges of boronic acid and boronic ester compounds. Expanding this method, reaction monitoring studies were performed to analyze the boronic acids present in the organic reaction mixtures obtained from the Suzuki coupling reaction, Arylation of amine, and Arylation of phenol reactions. The mobile phase used for this analysis was supercritical carbon dioxide modified by 8%-40% of methanol, which contained 20 mM aqueous ammonia (25%) as an additive, and the stationary phase used was 2-ethylpyridine-bonded silica. Overall runtime of the optimized method was 7 min with back pressure of 100 bar at a column temperature of 40°C. An extensive study was performed to optimize the various method parameters, such as columns, mobile phase modifier, additives, back pressure, and temperature. The validated SFC method was found to give a relative standard deviation of interday and intraday peak average area precision of each compound (A-E). The precision of the analytical method was evaluated based on the %RSD of the peak areas for each compound under both intraday and interday conditions. Despite slight variations, all intraday %RSD values were well within the acceptable range of analytical precision (<2%). The LOD and LOQ were in the range from 0.02 to 20 µg/mL and from 0.2 to 100 µg/mL respectively, for the five boronic acids compounds studied.