EVALUATION OF A NEW METHOD FOR URINARY FREE CATECHOLAMINES BY SOLID-PHASE EXTRACTION AND LIQUID-CHROMATOGRAPHY

A new commercial kit for the LC of urinary free catecholamines is compared with a column-switching method used in our laboratory for several years. The new method is based on solid phase clean-up of urine by cation-exchange cartridges, selective extraction of catecholamines and reversed-phase separation followed by electrochemical detection. The effect of sample pH on recovery, SPE cartridge capacity, linearity of calibration and similarity to aqueous solutions, are evaluated. To verify the LC analysis, the effects of injected volume, flow rate, column length and the dynamic voltammograms of the catecholamines, obtained with coulometric ED, have been studied. Intra-assay (n = 20) and inter-assay (n = 20) coefficients of variations (CV) were < 3.5 % and < 4.5 %, respectively. The correlation between the commercial kit and the column-switching method was followed for over 4 months on 800 samples of normal and pathological subjects and patients undergoing pharmacological treatment. The study of 106 potential interfering substances demonstrated that only catecholamine homologues are extracted. Only 4 substances, well resolved from compounds of interest, can appear in the chromatographic profile.