Direct injection analysis of epinephrine, norepinephrine, and their naturally occurring derivatives in serum by micellar liquid chromatography with electrochemical detection

The plasma level determination of catecholamines and their metabolites is necessary in studies aimed at evaluating neuroendocrine disorders. A micellar liquid chromatographic procedure was developed for the determination of epinephrine, norepinephrine, and their naturally occurring derivatives, metanephrine and nor-metanephrine, in serum samples using direct injection. The optimisation studies were performed in a C 18 column, using solutions containing sodium dodecyl sulphate (SDS) modified with propanol, butanol, or pentanol as mobile phases. The method proposed for the determination of these catecholamines used a hybrid micellar mobile phase of 0.075 M SDS-1.6% butanol-0.01 M phosphate buffer (pH 7) at 25 degrees C, and electrochemical detection. The serum samples were injected directly without any pretreatment and eluted in 14 min, in accordance with their relative polarities as indicated by their octanol-water partition coefficients. Calibration was linear in the 0.5-50 ng mL -1 range with r 2 >0.999. The limits of quantification (pg mL -1 ) in serum samples were within the 2.7-17 range. Repeatability and intermediate precision were tested for four different concentrations of the drugs, and the residual standard deviation values were below 2% for most of the assays. A study using UV detection is presented for comparison purposes.