Analysis of urinary catecholamines by high-performance liquid chromatography in the presence of labetalol metabolites.

Common sample preparation methods for catecholamines lead to contamination with metabolites of labetalol, an anti-hypertensive drug. When the extracts are analyzed by cation-exchange high-performance liquid chromatography, these metabolites are separated from the catecholamines, but their strong retention lengthens the analysis time. A procedure has been developed for complete removal of these drug metabolites from acidified urine by the use of XAD-4 resin. Loss of catecholamines is monitored by an internal standard. This pretreatment can be combined with extraction by weak cation-exchange resin and borate elution to simplify catecholamine analysis for patients receiving labetalol.