Evaluation of a New Method for the Analysis of Free Catecholamines in Plasma Using Automated Sample Trace Enrichment with Dialysis and HPLC

BACKGROUNDAnalysis of urinary free catecholamines was automated recently, but analysis of plasma samples posed special difficulties. The present study was undertaken to evaluate a new method for the automated analysis of plasma catecholamines.METHODSThe procedure is based on an improved sample handling system that includes dialysis and sample clean-up on a strong cation trace-enrichment cartridge. The catecholamines norepinephrine, epinephrine, and dopamine are then separated by reversed-phase ion-pair chromatography and quantified by electrochemical detection.RESULTSUse of a 740- microL sample is required to give the catecholamine detection limit of 0.05 nmol/L and analytical imprecision (CV) between 1.1% and 9.3%. The assay can be run unattended, although >12 h of analysis time is not recommended without cooling of the autosampler rack. Comparison (n = 68) of the automated cation-exchange clean-up with the well-established manual alumina procedure gave excellent agreement (mean, 3.78 +/- 2.76 and 3.8 +/- 2.89 nmol/L for norepinephrine and 0.99 +/- 1.72 and 1.08 +/- 1.78 nmol/L for epinephrine). Hemodialysis had no clear effect on plasma norepinephrine. Epinephrine concentrations were similar (0.05 < P < 0.1) in chronic renal failure patients (0.24 +/- 0.3 nmol/L; n = 15) and healthy controls (0.5 +/- 0.24 nmol/L; n = 31). Dopamine was not quantified, being usually <0.2 nmol/L.CONCLUSIONThe availability of such a fully automated procedure should encourage the more widespread use of plasma catecholamine estimation, e.g., after dialysis, exercise, or trauma/surgery and in the investigation of catecholamine-secreting tumors, particularly in the anuric patient.