Biopolymer-coated fused silica capillaries for high magnitude cathodic or anodic electro-osmotic flows in capillary electrophoresis

The manipulation of electroosmotic flow in capillary electrophoresis was achieved by coating the inner wall of a fused silica capillary with the biopolymers α-chymotrypsinogen A and dextran sulfate. Simple coating procedures were based on flushing the fused silica capillary with α-chymotrypsinogen A solution to obtain a α-chymotrypsinogen A coating, or to additionally coat with dextran sulfate solution to obtain a α-chymotrypsinogen A-dextran sulfate coating. The biopolymers α-chymotrypsinogen A coated capillary exhibited strong reversed (anodic) electroosmotic flow values as high as -81.7 × 10-9 m2 V-1 s-1 at pH 2.0. The α-chymotrypsinogen A -dextran sulfate coated capillary exhibited a cathodic EOF of 62.2 × 10-9m2V-1 s-1 which remained virtually unaltered over the pH range 2-9. Both coatings showed high stability, as demonstrated by electroosmotic flow reproducibility of 1.0% and 0.7% RSD (n = 50), respectively. The α-chymotrypsinogen A coating was found to be tolerant to 0.1 M HCl, whilst the α-chymotrypsinogen A-dextran sulfate coating was tolerant to 1 M NaOH, CH3OH and CH3CN. The coating-to-coating repeatability for the two coatings, as determined by the RSD of the resultant electroosmotic flow values, were 2.25% and 1.85% (n = 4), respectively. Four anions and five cations were used as test substances to examine the separation performance of the α-chymotrypsinogen A and α-chymotrypsinogen A -dextran sulfate coatings and high efficiencies (80,000 to 200,000 theoretical plates) and rapid separations were obtained. The separation of isomers of chloroaniline was carried out using the α-chymotrypsinogen A-dextran sulfate coating and a pH 2.5 electrolyte in about one third of the time needed when using a FS capillary. A α-chymotrypsinogen A coated capillary was used for ultra-rapid separation of nitrate and nitrite at acidic pH using a co-electroosmotic flow mode. The separation was completed in less than 10 s with a migration time reproducibility of 0.3% RSD (n = 10) and sub-μM detection limits.