Rapid determination of [guanidino-15N]arginine in plasma with gas chromatography--mass spectrometry: application to human metabolic studies.

A rapid gas chromatographic-mass spectrometric method for the determination of 15N in the guanidino nitrogens of arginine is described. The method is based on formation of the N-tetratrifluoroacetyl-arginine derivative. Approximately 0.15 mol% excess 15N can be detected in as little as 50 microliters of plasma with an average coefficient of variation of 8.8%. The possible fragmentation pattern of the N-tetra-trifluoroacetyl-arginine derivative is described. The method was applied to determine the appearance of 15N enrichment in plasma arginine in a healthy adult volunteer during a constant infusion of 15NH4Cl. A plateau level of 0.7 atom% excess was observed 2 h after the 15NH4Cl infusion was started.