Overcoming the Strong Sample Solvent Effect for Sustainability Measurement Challenges in Liquid Chromatography. Example for Bisphenol-A

This paper describes an approach to achieve low parts per billion (ppb) concentration level detection using a reversed-phase ultrahigh-performance liquid chromatographic ultraviolet absorbance detection method with large-volume feed injection (FI) for analytes in dichloromethane (DCM). FI is a novel technology that allows sample injection at a defined speed into the LC mobile phase. We demonstrate this approach for a mixture of bisphenol A and its diglycidyl ether derivatives in DCM. DCM is a very strong injection solvent at reversed-phase LC conditions and is typically immiscible with a starting reversed-phase gradient mobile phase containing a high percentage of water. As a result, reduced separation performance and even peak splitting are seen with classic flow-through injection. The method setup comprised an octyl-bonded core-shell stationary phase (150 × 4.6 mm i.d., 2.7 μm particle size) with a water/acetonitrile mobile phase gradient and an exceptionally high injection volume of 45 μL of DCM solution using FI. Optimization of feed speed (1%) and isocratic hold duration (4 min) was crucial for final separation conditions. FI delivered more than a 20-fold improvement in the limit of detection (LOD) compared to standard flow-through injection while maintaining peak resolution. The LOD of the final method ranged between 1 and 10 ppb in the polymer resin. This methodology has high potential for trace analysis in a large variety of applications that suffer from the "strong solvent effect".