Phospholipids covalently attached to silica particles as stationary phase in nano-liquid chromatography

Silica particles were covalently modified with phospholipids and used as packing material for nano-liquid chromatography (nano-LC). This modification involved aminopropylsilylation of the raw silica particles using 3-(aminopropyl)-triethoxysilane, covalent binding of glutaraldehyde molecules to the aminopropylsilylated particles, and finally covalent binding of different phospholipid vesicles containing primary amino groups to the iminoaldehyde silica particles. Capillaries with an inner diameter of 100μm were packed with phospholipid-coated silica particles using a slurry packing method. The packed capillaries were tested in nano-LC with UV-detection for the separation of acidic, neutral, and basic model analytes. The effect of the buffer ion on the retention factor of the analytes was evaluated using buffer solutions with constant ionic strength and pH. In addition, the effect of the volume of methanol in the mobile phase was studied. The calculated distribution coefficients (logK(D)) of the model compounds were in agreement with those reported in the literature. A good correlation between logK(D) values and octanol/water partitioning coefficients (P(o/w)) for neutral hydrophobic analytes was obtained proving the applicability of the method for predicting partitioning of the compounds with the biomembranes.