This paper discusses aspects arising on transferring liquid chromatography (LC) methods developed on conventional size columns to micro LC, i. e. the influence of batch‐to‐batch reproducibility of packing material, the nature of the column wall material, and the column inner diameter. It was shown that the nature of the column hardware as well as batches of Luna C18(2) packing material did not influence the retention of basic compounds. The batches of packing material, however, significantly influenced the peak shape for some compounds. The nature of the mobile phase buffer also showed an effect on peak shape. The column wall material as well as the column inner diameter did not reveal effects on the peak shape. Different packing densities were found for micro and conventional LC columns, i. e. the micro LC columns were less densely packed than the conventional LC columns. The study demonstrated that for the analysis of basic analytes similar separations are obtained using micro and conventional LC columns provided that the columns are packed from the same batch of packing material.
Gel permeation chromatography (GPC) has been investigated for the on line removal of proteins from plasma samples prior to their analysis by HPLC. The results show that GPC is a mild and effective way to remove proteins from plasma samples. It can very well be coupled on line to HPLC, providing the solutes are suitable for preconcentration on the analytical column itself or on a small pre-column, after the GPC. Under these conditions excellent reproducibility and accuracy can be obtained.
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