title: Parallel column ion exchange for post-separation pH modification in liquid chromatography. Application to barbiturates and miniaturization.
abstract: A new approach to the UV detection of barbiturates in high-performance liquid chromatography is demonstrated. The analytical system comprises an anion-exchange column inserted parallel to the injection valve and analytical column. One part of the acetate-containing mobile phase flows through the injection valve and analytical column to achieve the separation, the other part flows through the anion-exchange column where the acetate ions cause the release of hydroxide ions from this column. Finally, the alkaline stream from the anion-exchange column is recombined with the analytical column effluent. This results in an alkaline medium which can be favourable for many detection processes. A series of barbiturates, which show enhanced UV detectability at 254 nm in alkaline solution, was chosen to demonstrate the potential of such a method. Applications of this principle to the analysis of urine and plasma samples are described. In the system only one pump is needed for the separation and the post-column pH modification. A critical comparison between conventional scale and narrow-bore systems is made.
mesh_terms: D001463:Barbiturates / Q000032:analysis* / Q000097:blood / Q000652:urine; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D002853:Chromatography, Liquid; D006801:Humans; D006863:Hydrogen-Ion Concentration; D013056:Spectrophotometry, Ultraviolet
chemical_list: D001463:Barbiturates