Polymer Monolithic Column Research Articles

Rapid separation of nucleosides by capillary electrochromatography with a methacrylate-based monolithic stationary phase

Separation of nucleosides by capillary electrochromatography with a methacrylate-based monolithic column is described. Because the nucleosides are relatively hydrophilic compounds, chromatographic partition is very weak on non-polar stationary phases. A small quantity of organic modifier is usually required to increase their retention factors but, because the wettability of the stationary phase by the mobile phase is rather poor, bubble formation can be a significant problem. This situation was improved by use of a polymeric monolithic column with higher level charged monomer in the polymerization mixture, because of the presence of charged moieties on the surface of the monolithic stationary phase. The very high stability under conditions of very low organic modifier concentration used in the experiment showed that the wettability of the stationary phase by the mobile phase was satisfactory. The effect of pH, organic modifier content, and applied voltage on the separation was investigated. Baseline separation of six nucleosides was achieved within 4.5 min on this type of column. Because of the presence of charged moieties and butyl groups on the surface of the monolithic column, the mechanism of separation might involve both ion-exchange and hydrophobic interactions.

Effect of porosity and surface chemistry on the characterization of synthetic polymers by HPLC using porous polymer monolithic columns

Monolithic 50 × 4.6 mm ID poly(styrene-co-divinylbenzene), poly(glycidyl methacrylate-co-ethylene dimethacrylate), and poly(2,3-dihydroxypropyl methacrylate-co-ethylene dimethacrylate) columns have been tested in the high-performance liquid chromatography (HPLC) separation of polystyrenes and poly(methyl methacrylate) standards. The separation process involves precipitation of the macromolecules on the macroporous monolithic column followed by progressive redissolution and elution utilizing a gradient of the mobile phase. While very good separations of individual components of mixtures of both polystyrenes and poly(methyl methacrylates) can be readily achieved using poly(styrene-co-divinylbenzene) monolith, methacrylate-based columns do not afford good separations under identical conditions. This unexpected finding appears to be the result of significant differences between the porous properties and chemistries of the two types of monolithic materials.

Profiling of impurities in heroin by capillary electrochromatography and laser-induced fluorescence detection

Capillary electrochromatography (CEC) with laser-induced fluorescence (LIF) detection was investigated for the analysis of acidic and neutral impurities in heroin. The phenanthrene-like heroin impurities exhibit high native fluorescence when excited with a doubled argon ion laser (operating at 257 nm). The limit of detection for acetylthebaol is 66 pg ml −1. CEC–LIF analysis of heroin samples of different geographical origin gave distinguishable peak-enriched chromatograms. A sulfonic acid C 12 polymer monolith column provided similar resolving power to a 1.5 mm non-porous ODS column for the isocratic analysis of a refined heroin sample. Analysis of a crude heroin sample via a multi-step gradient CEC resolved a significantly higher number of peaks than gradient high-performance liquid chromatography or micellar electrokinetic capillary chromatography.