Viscosity contrast effects in analytical scale chromatography - Evidence and impact

A Flexible Kenics Mixer for Applications in Liquid Chromatography

Miniaturization of liquid chromatography could help enhance sensitivity, reduce solvent usage, and detect small quantities of peptides. However, it demands better sample homogenization of the mobile phase. We here developed a mixer design based on the inline Kenics geometry, consisting of a periodic arrangement of twisted blades placed inside a cylindrical capillary that repeatedly cut and stack fluid elements to achieve rapid mixing in laminar flow regimes. The mixer design was optimized with respect to the twist angle and aspect ratio of the mixing units to achieve complete mixing at minimum pressure load cost. Results suggest that for optimal designs, for a mixer volume of ~70 μL, complete mixing is achieved within a distance smaller than 4 cm for a broad set of flow rate conditions ranging from 75 μL·min^-1 to 7.5 mL·min^-1. A salient feature that we introduce and test for the first time is the physical flexibility of the cylindrical capillary. The performance of the design remained robust when the mixing section was not rigid and bent in different topologies, as well as when changing the chemical composition of the mobile phase used.

The use of zeolite 13X as a stationary phase for direct determination of water in organic solvents by high-performance liquid chromatography

High-performance liquid chromatography (HPLC) method for direct determination of water impurities in various organic solvents using a column (50 × 4.6 mm, ID) packed with 5 μm faujasite and methanol as an eluent was developed. Detection of the water peaks was performed by using either refractometric or indirect spectrophotometric method at 204 nm. In the first case the limit of detection (LOD) and limit of quantitation (LOQ) were 0.001 wt% and 0.0033 wt%, respectively for a sample volume of 20 μL. A linear calibration plot (R² = 0.9998) for the water content between 0.01 and 9.55 wt% was obtained. The developed method was applied for the direct analysis of various polar organic solvents including acetonitrile, nitromethane, 1,4-dioxane, 2-ethoxyethanol, methanol, dimethyl sulfoxide (DMSO), ethanol and 2-propanol.