Hydrophilic interaction liquid chromatography for the separation of acidic agricultural compounds

Organic acids with very low pKa require extremely low pH conditions to achieve adequate retention in reversed-phase liquid chromatography, but an extremely low pH mobile phase can cause instrument reliability problems and limit the choice of columns. Hydrophilic interaction chromatography is a potential alternative to reversed-phase liquid chromatography for the separation of organic acids using more moderate conditions. However, the hydrophilic interaction chromatography separation mechanism is known to be very complex and involves multiple competing mechanisms. In the present study, a hydrophilic interaction chromatography column packed with bare silica core-shell particles was used as the separation column and six agricultural organic acids were used as model analytes to evaluate the effects of buffer concentration, buffer pH, and temperature on sample loading capacity, selectivity, retention, and repeatability. It was found that using a higher concentration of buffer can lead to a significant improvement in the overall performance and reproducibility of the separation. Investigation of column equilibration time revealed that a very long equilibration time is needed when changing mobile phase conditions in between runs. This limitation needs to be acknowledged in hydrophilic interaction chromatography method development and sufficient equilibration time needs to be allowed in method scouting.