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.