Comparison of core–shell particles and sub-2 μm fully porous particles for use as ultrafast second dimension columns in two-dimensional liquid chtomatography

• Core–shell and sub 2 μm fully porous particles were compared under typical LC × LC conditions.
• Peak capacity was the metric used to determine which particle type is the better choice for LC × LC.
• Equal or slightly better peak capacities were achieved with the core–shell type columns.
• Higher F can be used on core–shell particles compared sub 2 μm resulting in shorter reequilibration times.
• Fast reequilibration of core–shell particles gives them a small but definite edge over sub 2 μm particles.

The peak capacity of small columns packed with 2.7 μm core–shell particles and 1.8 μm fully porous particles were compared at high temperatures using very steep (fast) gradient conditions and quite high linear velocities using the same instrument configuration as used to transfer first dimension effluent to the second dimension column as done in on-line comprehensive two-dimensional liquid chromatography. The experimental peak capacities of small columns (2.1 mm × 30 mm) packed with both types of particles were measured with fast gradients (9 s to 2 min) at high temperature (95 °C) using both the same flow rate (1.75 mL/min) and then at different flow rates at the same pressure (400 bar). Equal or slightly better peak capacities were achieved with the core–shell particle columns as compared to the fully porous particle columns at the same backpressure or the same flow rate. However, core–shell particles offer a real advantage over the smaller, fully porous particles because they can be operated at higher flow rates thus gradient mixer flush out and column reequilibration can be done in less time thereby allowing a greater fraction of the second dimension cycle time to be dedicated to the gradient time.