Development of a large-volume, membrane-based injection system for gradient elution micro-liquid chromatography

A membrane unit which can be used to inject a large volume of sample solution was developed to facilitate reproducible and accurate gradient elution in micro-high-performance liquid chromatography (micro-HPLC). Since the membrane unit has a very low void volume, it facilitates the effective concentration of analytes in large sample volumes. Gradient elution micro-HPLC with the membrane unit allowed the efficient separation of n-alkyl benzoates, used as test samples, in a short time without marked gradient delay. In this study, the membrane unit could be loaded with up to 50 μg of n-hexyl benzoate, and more than 500 μL of sample solution could be applied. In about 50 chromatographic runs, the relative standard deviation (RSD) of the relative retention time of n-hexyl benzoate with respect to methyl benzoate was 0.530%.