Development of Novel Capillary Coating Based on Physical Adsorption for Capillary Electrophoresis
A simple and stable capillary coating based on physical adsorption called "successive multiple ionic-polymer layer (SMIL)" coating was developed and evaluated. 1 An ionic polymer dextan sulfate (DS) was adsorbed to the inner wall of a capillary by sandwiching cationic polymer polybrene (PB) between the DS and the unmodified capillary wall. The DS coated capillary was expected to show pH-independent electroosmotic flow (EOF) because DS has sulfonic groups. The endurance of the SMIL coating was
... SMIL coating was improved in comparison with the conventional physical adsorption. The pH-independent EOF of the DS coated capillary showed new applications especially in acidic regions where EOF of the uncoated capillary could not be generated. Experimental Materials The coating reagent polybrene (PB) was from Fluka (Tokyo, Japan) and dextran sulfate (DS) was from Sigma (St. Louis, MO, USA). Phenol, p-toluensulfonic acid, acetylsalicylic acid (aspirin) and quinine hydrochloride were from Wako (Osaka, Japan). Formamide (Pharmacia Biotech, Uppsala, Sweeden) was used as an EOF marker. Others were of reagent grade. Equipment CE was performed with a Beckman P/ACE 2100 (Beckman Instruments, Fullerton, CA, USA). The uncoated fused silica capillaries of 75 mm i.d., 27 cm were from GL Sciences (Tokyo, Japan). Capillaries were thermostated at 25˚C both during the coating and analyses. Sample injections were performed by pressure (0.5 psi; 1 psi=6894.76 Pa) for 2.0 s. Coating steps for SMIL were performed by the rinse function of the Beckman CE system. Procedure of SMIL coating Procedure of SMIL coating was performed as follows. The capillaries were rinsed by 1.0 mol/l sodium hydroxide, followed by rinsing the aqueous PB solution as the first layer and the aqueous DS solution as the second layer. CE analyses with the SMIL coated capillaries were performed after rinsing by pure water. Results and Discussion When PB solution was flushed through the capillary, EOF was found to be reversed. Then, when DS solution was flushed over PB layer, EOF was reversed again. A disadvantage of physical adsorption coating is its low endurance 2 , while it has advantages of simple coat-Keywords Stable coating, polybrene, dextran sulfate, pH-independent electroosmotic flow † To whom correspondence showld be addressed. Fig. 1 The endurance of SMIL-PB and SMIL-DS capillary. Conditions: applied voltage, +7 kV; buffer, phosphate buffer at pH 3.0 (I=0.05); capillary,75 mm i.d.´27 cm (20 cm effective length).