Radioenzymatic assay of catecholamines in plasma after a preliminary solvent extraction compared with an analogous liquid-chromatographic method.

Catechol-borate complexation and ion-pair formation combined with organic solvent extraction as preliminaries to radioenzymatic assay (REA) with catechol-O-methyltransferase-catalyzed methylation allows the quantification of catecholamines in plasma samples of any volume. We attained improved detection limits for 1-mL samples: 9 ng/L for norepinephrine (NE), 8 ng/L for epinephrine (E), and 11 ng/L for dopamine (DA). Precision data resemble those obtained by REA for small-volume samples. Comparison with a liquid chromatography-electrochemical detection (LCEC) technique showed the two methods to be equivalent for NE and E determinations, but DA estimations were lower by REA than by LCEC.