Dead volume determination of the HPLC monolithic rod columns with organic sorbents

Features of the dead (void) volume <i>V</i>₀ determination of chromatographic columns with organic sorbents were considered. Two monolithic columns were studied: based on divinylbenzene – styrene (DVB-St), and based on 1-vinyl-1,2,4-triazole (VTr). Two methods were used for determination of columns’ void volume: (1) measuring the retention time of unretained components and (2) quantitative determination of the mobile phase (MP) components in the column (direct method). The first method depends on both the component nature and the MP composition, whereas the direct method makes it possible to obtain the void volume value that does not change in a wide range of the MP polarity. For the VTr column, the void volume does not change when the acetonitrile/water MP composition is varied from 100/0 to 20/80. For the DVB-St column, the void volume depends on the MP composition. This occurs due to swelling of the sorbent in a good solvent (high content of acetonitrile) and its shrinking in a poor solvent (high content of water). The absence of the void volume dependence on MP composition for the VTr column can be attributed to 1,2,4-triazole fragments hydrophility. As a result, the monolith is not shrunk at the water excess in the MP.