Improving the performance of HPLC–MS using radial flow splitting columns: the analysis of caffeine in energy drinks

The management of the mobile phase at the interface between high-performance liquid chromatography (HPLC) and mass spectrometry (MS) has always been important. Due to the necessity to operate the MS under a state of high vacuum, the removal of the mobile phase from the HPLC has always presented as a problem. Hence, the chromatographic separation is limited in flow rate by the capacity of the MS to remove the subsequent mobile phase vapor prior to solute transport to the detection source. Although the efficiency of solvent removal at the interface between HPLC and MS has improved over the decades, there is an increasing requirement for HPLC columns to operate at higher linear flow velocities. If this is to be done without the use of narrow bore or capillary columns, this necessitates the use of higher volumetric flow rates. It is this disparity that continues to make the marriage between HPLC and MS problematic. Herein, we have tested the performance of HPLC with MS detection by incorporating recently developed radial flow stream (RFS) splitting end fittings to standard HPLC columns. These RFS end fittings enable the total flow of the mobile phase to be split so that only the central portion is directed to the MS, which actually increases the efficiency in the separation step due to the flow profile in the column. In essence, the incorporation of the RFS end fittings enabled a threefold increase in analytical throughput compared to standard HPLC columns without any loss in quantitative metrics, and other key findings are also presented.