Evaluation of temperature programming for gradient elution in packed capillary liquid chromatography coupled to electrochemical detection

A miniaturized amperometric detector compatible with temperature-programmed packed capillary liquid chromatography has been constructed and evaluated. Temperature programming could successfully be used as a tool for retention control, providing gradient action that did not influence the detector per formance. A 7-mum single carbon fiber was utilized as working electrode and detection was performed in a 50-mum. i.d. fused silica detection capillary which also functioned as restriction capillary. Separation of tyrosine, 3- (3,4-dihydroxyphenyl) alanine, 3-chloro-tyrosine and 3-NO2-tyrosine was ach ieved in 6 min using a temperature program from 30 degreesC to 100 degreesC with a ramp of 8 degreesC/min on a 25 cm. 0.32 mm. i.d. column packed with 3 mum Hypersil ODS. The mobile phase consisted of 50 mM citric acid (pH 3. 10)-methanol (95 + 5, v/v), and the mass limit of detection was in the rang e 1-5 pg using 1.2 V vs the Ag/AgCl reference electrode. (C) 2001 John Wile y & Sons, Inc.