1.1 μm Superficially porous particles for liquid chromatography: Part II: Column packing and chromatographic performance

• UNC particles had similar efficiency as the commercially available products tested.
• Aggregating slurry solvents, such as methanol, produced more efficient columns.
• A 25 mg/mL slurry produced columns with increased efficiency, hmin = 2.6.
• In-solution optical microscopy was found to accurately predict column efficiency.

The predicted advantages of superficially porous particles over totally porous particles are decreased eddy dispersion, longitudinal diffusion, and resistance to mass transfer contributions to the theoretical plate height. While sub-2 micron superficially porous particles are commercially available, further improvements in performance are predicted by decreasing the particle diameter and decreasing the porous layer thickness. 1.1 μm superficially porous particles with 187 Å pores have been synthesized using a layer-by-layer method tuned for production of smaller diameter particles. Following synthesis, these particles were packed into 30 μm i.d. capillary columns and their chromatographic performance evaluated using electrochemical detection. Based on the initial studies, the column efficiency did not meet theory, but was similar to the commercially available products tested. It is believed that the column packing process plays a critical role in the sub-par column performance. To determine if column efficiency could be predicted by solvent-particle interactions, in-solution optical microscopy and sedimentation velocity of particles in various slurry solvents were investigated and compared to column performance. Aggregating slurry solvents, such as methanol were found to produce columns with increased efficiency. The hmin for a column packed with an acetone slurry and a methanol slurry at 3 mg/mL were found to be 6.3 and 3.5, respectively. Increasing the slurry concentration to 25 mg/mL further improved the efficiency, producing a column with an hmin of 2.6. These efficiency results were accurately predicted by in-solution optical microscopy.