A novel fully automated method for the measurement of sulphoconjugated catecholamines in urine using the Gilson ASTED-XL sample preparation system and high-performance liquid chromatography

Dopamine is produced in the kidney where it causes sodium excretion. Dopami ne sulphate is deconjugated in vivo, and may be a physiological reservoir f or this active renal dopamine. To investigate the role of dopamine and dopa mine sulphate in sodium homeostasis we have developed a fully automated HPL C assay for free, total and sulphoconjugated dopamine. Using the Gilson AST ED-XL sample preparation unit, with temperature controlled racks, urinary f ree and total dopamine are measured pre-and postincubation with arylsulphat ase. Dopamine sulphate is calculated from the difference between free and t otal measurements. Acidified 24 h urines are processed automatically. Free dopamine assay follows buffering to pH 7.0, addition of internal standard, addition of EDTA to stabilize free catecholamines at neutral pH, and incuba tion at 37 degrees C for 30 min. This mixture is trace enriched on a HEMA-S B TEC prior to ion-paired HPLC with amperometric detection. To measure tota l dopamine the entire process is automatically repeated with addition of ar ylsulphatase (400 mU/mL urine) at the beginning of the 37 degrees C incubat ion. The working range of the assay is up to 7 mu mol/L total dopamine. Wit hin-and between-run imprecision for dopamine sulphate is less than 3 and 7% respectively. Median dopamine sulphate excretion in 12 normotensive subjec ts was 4.3 mu mol/24 h. Copyright (C) 1999 John Wiley & Sons, Ltd.