| The research presented here presents a novel detection method for making direct on-column measurements of column performance. By matching the refractive indices of the mobile phase, the stationary phase and the material of the bed enclosure, one can render transparent to the eye the chromatographic column which is normally opaque in nature. High definition on-column detection becomes feasible by using a photographic detector instead of the conventional post-column, on-line (UV/Vis or similar) detector. Quantitative information regarding the concentration distribution in the band is obtained by utilizing optical scanners to obtain a digital image and computer imaging software.;The performance of the photographic detection method is compared to that of regular detection procedures. A calibration procedure is illustrated and suitable corrections are introduced to account for the transverse variation of the optical path length, as a result of using a cylindrical detector cell (the column itself), and for the refraction of light due to the differences between the refraction indices of the glass wall and the liquids involved.;A number of columns, as similar as possible, were fitted with different 2 mum and 10 mum porosity stainless-steel frits of similar and varied sizes. The 2 mum frits produced more dramatic effects overall on the band shape than the coarser frits. The smallest diameter frit induced severely parabolic sample distributions at the column inlet compared to the larger frit. Local axial dispersion coefficient values, expressed as local reduced plate height, were calculated.;The study also shows that, under conditions where viscous fingering is prevalent, the design of the inlet header has little influence on the outcome of the viscous fingers. Two types of headers were studied. The first contained a small diameter inlet frit, which localized the majority of the sample in or near the central region of the column. The second header contained a wide frit and produced a more uniform radial distribution of the sample. In both cases, the extent of viscous fingering was essentially the same. |
