Achieving a Peak Capacity of 1800 Using an 8 m Long Pillar Array Column

In the present study, the peak capacity potential of ultralong porous cylindrical pillar array columns is investigated. Coupling 4 columns of 2 m long allows for working near the minimal separation impedance of small molecules under retained conditions at a maximal pressure load of 250 bar. Minimal plate heights of H = 5.0 μm, H = 6.3 μm, and H = 7.7 μm were obtained for uracil (unretained), butyrophenone (k = 0.85), and valerophenone (k = 1.94), respectively, corresponding to a number of theoretical plates of N = 1.6 × 10⁶, N = 1.2 × 10⁶, and N = 1.0 × 10⁶. The optimal linear velocities were 0.60 mm/s for a retained compound and 0.74 mm/s for an unretained compound. Based on a mixture of 9 compounds, the peak capacity n_c was determined as a function of gradient time (t_G). Peak capacities (t_G-based) of 1103 and 1815 were obtained when applying 650 min and 2050 min gradients (t_G/t₀ = 4.5 and 14, respectively, with t_G as the gradient time and t₀ as the void time). These values are much higher than earlier reported peak capacity values for small molecules.