Capillary chromatography based on tube radial distribution of aqueous–organic mixture carrier solvents

A capillary chromatography system was developed using open capillary tubes made of fused-silica, polyethylene, or poly(tetrafluoroethylene), and an aqueous–organic mixture (water–acetonitrile–ethyl acetate mixture) as a carrier solution. Model analyte mixture solutions, such as 2,6-naphthalenedisulfonic acid and 1-naphthol, Eosin Y and perylene, bis[N,N-bis(carboxymethyl)aminomethyl]fluorescein and 1,1’-bi-2-naphthol, and 2,7-naphthalenedisulfonic acid and p-nitroaniline, were injected into the capillary tube by a gravity method. The analyte solutions were subsequently delivered through the capillary tube with the carrier solution by a micro-syringe pump. The system worked under laminar flow conditions. The analytes were separated through the capillary tube and detected on-capillary by an absorption detector. For example, 2,6-naphthalenedisulfonic acid and 1-naphthol were detected in this order with a carrier solution of water–acetonitrile–ethyl acetate (volume ratio 15:3:2), while they were detected in the reverse order with a carrier solution of water–acetonitrile–ethyl acetate (volume ratio 2:9:4). The other analyte solutions were similarly separated by the system. The elution times of the analytes could be easily reversed by changing the component ratio of the solvents in the carrier solution.