Micro-flow separation system using an open capillary tube that works under laminar flow conditions.

A micro-flow separation system was developed using an open capillary, fused-silica or polyethylene tube, and an aqueous-organic mixture (water-acetonitrile-ethyl acetate mixture) as a carrier solution. A model analyte solution containing 2,6-naphthalenedisulfonic acid and 1-naphthol was injected into the capillary tube by a gravity method. The analyte solution was 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. 2,6-Naphthalenedisulfonic acid and 1-naphthol were detected in this order with a carrier solution of water-acetonitrile-ethyl acetate (15:3:2 volume ratio), while they were detected in the reverse order with a carrier solution of water-acetonitrile-ethyl acetate (2:5:9 volume ratio) using a fused-silica capillary tube. Similar separation behavior, i.e., that the elution times of the analytes could be easily reversed by changing the component ratio of the solvents in the carrier solution, was observed with a polyethylene capillary tube.