Covalent binding of phospholipid vesicles on fused silica capillaries for electrochromatography

A rapid method for covalent binding of phospholipids with primary amino groups on fused silica capillaries was developed. In the 8 hour coating procedure the reaction product of aminopropylsilylation of the silanol groups of the fused silica capillary reacts with glutaraldehyde giving an imidoaldehyde which then reacts with the primary amino group of the phospholipid. Various types of liposomes with a broad range of composition and concentration were tested, and the role of primary amino groups in lipids was clarified. Since only 2.5% of lipids with primary amino groups were needed for stable covalent binding of liposomes to the fused silica capillary wall, the method allowed fine-tuning of the lipid composition to mimic given in vivo conditions. The optimized coating showed good stability, with intra-day and inter-day repeatability of electroosmotic flow equal to 2.36% RSD (n = 15) and 3.56% RSD (n = 3), respectively. The capillary to capillary reproducibility was 5.66% RSD (n = 3). The thickness and other properties of the attached liposome layer were measured using quartz crystal microbalance (QCM) technique. The capillary surface with covalently attached liposomes acted as a high throughput assay for the determination of interactions between the phospholipid bilayer and the aqueous phase. A model set of structurally diverse drugs was separated in the liposome coated capillary. The retention factors and distribution values were used as indicators of affinity of the drugs toward liposomes.