Evaluation of a new method for the analysis of free catecholamines in plasma using automated sample trace enrichment with dialysis and HPLC

Background: Analysis of urinary free catecholamines was automated recently, but analysis of plasma samples posed special difficulties. The present stu dy was undertaken to evaluate a new method for the automated analysis of pl asma catecholamines. Methods: The procedure is based on an improved sample handling system that includes dialysis and sample clean-up on a strong cation trace-enrichment c artridge. The catecholamines norepinephrine, epinephrine, and dopamine are then separated by reversed-phase ion-pair chromatography and quantified by electrochemical detection. Results: Use of a 740-mu L sample is required to give the catecholamine det ection limit of 0.05 nmol/L and analytical imprecision (CV) between 1.1% an d 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 = 6 8) of the automated cation-exchange clean-up with the well-established manu al 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 norepinephr ine. Epinephrine concentration were similar (0.05 < P < 0.1) in chronic ren al 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. Conclusion: The availability of such a fully automated procedure should enc ourage the more widespread use of plasma catecholamine estimation, e.g., af ter dialysis, exercise, or trauma/surgery and in the investigation of catec holamine-secreting tumors, particularly in the anuric patient, (C) 1999 Ame rican Association for Clinical Chemistry.