Possibility of large volume injection and band focusing in UHPLC.

New shell-type stationary phases are widely used in fast chromatographic measurements. These columns provide more efficient separation, when applied in a conventional high-performance liquid chromatography instrument, than columns with fully porous particles, and the volume overload of core-shell particles is 60% of the value obtained for fully porous particles. Additionally, to achieve adequate sensitivity, the injection volume cannot be significantly decreased. This study presents a systematic evaluation of the possibilities of large volume injection onto columns packed with 2.6 µm Kinetex C18 shell particles. The effect of volume overload on performance of columns with different lengths (50, 100 and 150 mm) is studied. Column efficiency is compared under isocratic, pulse gradient and gradient conditions. The application of large volume injection in practice is also reported. The most suitable among the tested large volume injection techniques was the gradient elution, which was applied to determine amino acid enantiomers from fruit juice.

Fast liquid chromatography: the domination of core-shell and very fine particles.

Columns packed with sub-2 µm totally porous and sub-3 µm core-shell particles are very widespread nowadays to conduct fast and efficient separations. In order to carry out really fast separations, short (5 cm long) columns are very popular today. The goal of this paper is to review the recent possibilities in fast or "ultra-fast" HPLC by applying short and narrow bore columns packed with modern core-shell and very fine fully porous particles. Efficiency data obtained with these recently commercialized columns from the past few years are collected, discussed and compared in terms of potential separation time and efficiency. The reasons of the success of these columns are presented. This paper also shows that theoretically expected efficiency is sometimes compromised in practical work especially in the case of narrow bore columns. The extra-column dispersion of a given LC system can also dramatically decrease the performance of small columns. It is not possible to utilize the real efficiency of these small columns in spite of their really high intrinsic separation power.

Interaction of phenol and dopamine with commercial MWCNTs.

We report the adsorption of phenol and dopamine probe molecules, from aqueous solution with NaCl, on commercial multiwall carbon nanotubes (MWCNT) and on their carboxylated derivative. The nanotubes were fully characterized by high resolution transmission electron microscopy (HRTEM), small angle X-ray scattering (SAXS), potentiometric titration, electrophoretic mobility, and nitrogen adsorption (77K) measurements. The experimental pollutant isotherms, evaluated using the Langmuir model, showed that only 8-12% and 21-32% of the BET surface area was available for phenol and dopamine, respectively, which is far below the performance of activated carbons. Influence of the pH was more pronounced for the oxidized MWCNT, particularly with dopamine. The strongest interaction and the highest adsorption capacity occurred at pH 3 with both model pollutants on both types of nanotubes. Although the surface area available for adsorption is far lower in MWCNTs than in activated carbons, it is nonetheless substantial. In particular, delayed release of toxic molecules that are either adsorbed on the surface or trapped in the inner bore of such systems could constitute an environmental hazard. The need for further adsorption studies with regard to their environmental aspects is therefore pressing, particularly for MWCNTs in their functionalized state.

Comparative study of new shell-type, sub-2 micron fully porous and monolith stationary phases, focusing on mass-transfer resistance.

Today sub-2 microm packed columns are very popular to conduct fast chromatographic separations. The mass-transfer resistance depends on the particle size but some practical limits exist not to reach the theoretically expected plate height and mass-transfer resistance. Another approach applies particles with shortened diffusion path to enhance the efficiency of separations. In this study a systematical evaluation of the possibilities of the separations obtained with 5 cm long narrow bore columns packed with new 2.6 microm shell particles (1.9 microm nonporous core surrounded by a 0.35 microm porous shell, Kinetex, Core-Shell), packed with other shell-type particles (Ascentis Express, Fused-Core), totally porous sub-2 microm particles and a 5 cm long narrow bore monolith column is presented. The different commercially available columns were compared by using van Deemter, Knox and kinetic plots. Theoretical Poppe plots were constructed for each column to compare their kinetic performance. Data are presented on polar neutral real-life analytes. Comparison of a low molecular weight compounds (MW=270-430) and a high molecular weight one (MW approximately 900) was conducted. This study proves that the Kinetex column packed with 2.6 microm shell particles is worthy of rivaling to sub-2 microm columns and other commercially available shell-type packings (Ascentis Express or Halo), both for small and large molecule separation. The Kinetex column offers a very flat C term. Utilizing this feature, high flow rates can be applied to accomplish very fast separations without significant loss in efficiency.