Visualization of sample introduction in liquid chromatography columns - The effect of the frit diameter

A previously developed on-column detection technique using 35 mm SLR camera s [J. Chromatogr. A 826 (1998) 1] was employed to visualize colored sample bands as they elute through frits of differing diameter. Head fittings cont aining a 4.0 mm frit and a 15.9 mm frit were mounted in a 17 mm I.D. glass column packed with C-18 silica with an average particle size of 21 mu m. A carbon tetrachloride mobile phase of matching refractive index to that of t he silica provides clarity along the column diameter during band migration. The photographs of the migrating sample zones were scanned and analyzed wi th appropriate imaging software. The smallest diameter frit induced severel y parabolic sample distributions at the column inlet compared to the larger frit. Local axial dispersion coefficient values, expressed as local reduce d plate height, were calculated as well as local zone velocities at the col umn inlet. The results demonstrate clearly the need to match the diameter o f the inlet frit to the I.D. of the column so as to avoid the initial onset of zone broadening due to the frit. (C) 1999 Elsevier Science B.V. All rig hts reserved.