DETERMINATION OF CATECHOLAMINES AS AMINOCHROMES BY MICELLAR LIQUID-CHROMATOGRAPHY WITH THERMAL LENS SPECTROPHOTOMETRIC DETECTION

The determination of catecholamines (CAs) using micellar liquid chromatography with thermal lens spectrophotometric detection has been studied. CAs are oxidized with hexacyanoferrate(III) to aminochromes which are separated with a mobile phase of 0.05 M sodium dodecyl sulphate, 7 % propanol and 0.03 M citrate buffer, pH 4.8, on a partially endcapped C-18 column. The aminochrome-micelles and aminochrome-stationary phase association constants are evaluated. Using the 488 nm line of an Ar+ laser with 250 mW pump power the limits of detection are about 4 ng mL-1. The technique is applied to the determination of unconjugated CAs in urine using isoproterenol as internal standard.