Towards a generic variable column length method development strategy for samples with a large variety in polarity

• Proof-of-principle for the serial coupling of HILIC and reversed-phase separations.
• Two one-dimensional separations coupled on a single UHPLC system.
• Switching valves and mixers are used to couple orthogonal phases.
• Mobile phases of orthogonal phases can be almost completely reversed inline.
• Applicability demonstrated for pharmaceuticals found in surface and waste water.

The development of a novel set-up for the sequential analysis of compounds with a large variety in polarity on HILIC and reversed-phase columns, coupled in series, is discussed. For this purpose, a commercially available ultra-high performance LC system, equipped with two switching valves is employed. The switching valves allow connecting the HILIC and reversed-phase columns either in series or in parallel to the system. An interface to couple the HILIC and reversed-phase columns is developed and optimized. The sample is first injected onto a HILIC column. Apolar compounds in the sample are not retained and will elute close to or within the void volume of the HILIC column. Accurate switching of the valves allows redirecting these compounds towards a trap loop while more polar compounds are retained and separated on the HILIC column. After separation and detection of the polar compounds, the configuration of the valves is switched again to direct the apolar compounds from the trap loop towards a reversed-phase column for separation. To deal with the incompatibility of the mobile phases of HILIC and reversed-phase column separations, commercially available Jet weaver mixers are included in the set-up to allow for an intermediate solvent exchange. The proof-of-concept is demonstrated for the analysis of pharmaceuticals that can be found in waste water and surface water. It is demonstrated that the set-up provides robust analyses with peak capacities that are intermediate to one-dimensional and two-dimensional separations.