Measurement of nitrite and nitrate in plasma, serum and urine of humans by high-performance liquid chromatography, the Griess assay, chemiluminescence and gas chromatography-mass spectrometry: interferences by biogenic amines and N(G)-nitro-L-arginine analogs.

In this paper, the HPLC method for the measurement of nitrite and nitrate in serum of humans newly reported by El Menyawi et al. is discussed, especially in regard to the extremely low nitrate levels measured in serum of healthy humans. From the discussion, it is concluded that: (1) Biogenic amines at physiological concentrations do not significantly interfere with the batch Griess assay. (2) The HPLC method of El Menyawi et al. does not reveal accurate levels for serum nitrate. (3) In serum and plasma of healthy humans. nitrate ranges within 15-70 μM. (4) Exogenous N G -nitro-L-arginine analogs can interfere with the measurement of nitrate in human plasma and urine by the batch Griess assay, chemiluminescence and GC-MS; interferences can be effectively eliminated by solid-phase extraction on cation-exchangers.