STABLE CAPILLARY COATING WITH SUCCESSIVE MULTIPLE IONIC POLYMER LAYERS

A stable modification of the inner wall of a fused silica capillary wa s established by a simple coating procedure, successive multiple ionic -polymer layer (SMIL) coating. An anionic polymer was tightly fixed to the capillary wall by the SMIL coating, in which a cationic polymer w as sandwiched between the anionic polymer and the uncoated fused silic a capillary by noncovalent bonding. The SMIL-coated capillary showed a long lifetime. The endurance of the SMIL-coated capillary was more th an 100 runs, and it was also tolerant to organic solvents, 1 M NaOH, a nd a surfactant. The coating efficiency did not depend on capillary so urces, and the relative standard deviation of capillary-to-capillary r eproducibility was less than 1%. In this study, dextran sulfate (DS) w as used as the anionic polymer, and Polybrene was used as the cationic polymer for SMIL, modification. The DS-modified capillary (SMIL-DS ca pillary) exhibited a pH-independent electroosmotic now (EOF) from anod e to cathode in the pH range of 2-11. The SMIL-DS capillary showed goo d performance for acidic protein analyses under physiological conditio ns (pH 7.4). Also, the presence of EOF under acidic conditions permitt ed new applications. Simultaneous separations of cationic, anionic, an d neutral amino acids were achieved by capillary zone electrophoresis, and separations of cresol isomers were achieved by micellar electroki netic chromatography under the acidic conditions. The SMIL-DS capillar y was also useful for fast and precise determination of the pK(a) of a cidic functional groups.