PREPARATION OF SMALL-DIAMETER THICK-FILM CAPILLARY COLUMNS FOR MICROCOLUMN SEPARATIONS

Open tubular columns of 25 and 50 mum i.d. have been coated with up to 2 mum thick layers of SE-54 (lowest beta-value = 6.25). Filling of th e columns and evaporation of the solvent were studied as a function of column length and time. Since the viscosity of the stationary phase s olution increases exponentially with concentration, the filling proces s becomes time consuming and high filling pressures are required. The evaporation or coating speed is shown to be controlled by the resistan ce to mass transfer of the solvent vapor through the coated sections o f the column. For 25 and 50 mum i. d. columns, experimental evaporatio n times deviate little from theoretical predictions. Almost no influen ce of the stationary phase on the coating speed was observed. The tran sition from mass transfer limited coating speed to heat transfer limit ed coating speed is illustrated using literature data.