Introducing a Depressurization Step in Online LCxSFC Modulation

New online LCxSFC valve technologies have recently been developed, based on the transfer of the first-dimension eluent either in the CO₂ stream or in the cosolvent stream of the SFC dimension. While using the appropriate valve configuration greatly improved peak shapes, the reduction of the analysis time remained a challenge. A compromise between high first-dimension flow rate, to reduce gradient time, and low second-dimension injected volume, to limit injection effects, is to implement a flow split upstream of the valve. The so-called "modifier stream" configuration, in which the transfer loops are filled with liquid at all times, facilitates split integration as it resembles typical LCxLC interfaces. On the other hand, the so-called "CO₂ stream" configuration must be selected when protic mobile phases are used in both dimensions. In this configuration, the presence of pressurized CO₂ in the transfer loop forbided the use of splits so far to avoid sample pushback and loss through the waste outlet. The present work studies the feasibility of implementing a split when using the "CO₂ stream" configuration. Modifying the interface by adding a second valve to control CO₂ depressurization upstream of the loop filling phase has demonstrated conclusive results, avoiding gas escape and sample loss. Repeatability tests on a real sample application have been successful and highlight this new interface's performance.