Simultaneous analysis of citrulline and arginine in serum and tissue

We developed a method for simultaneously determining l-citrulline and l-arginine levels in serum and tissue samples using RP-HPLC with ultraviolet (UV) detection. The serum was deproteinized by trichloroacetic acid and heat; the tissue was homogenized by trichloroacetic acid and deproteinized as the same as serum. Phenyl-isothiocyanate (PITC) solution was used as derivatization reagent and a gradient elution was carried out. The linearity for l-arginine and l-citrulline ranged from 0 to at least 1000μmol/L. R2 values were above 0.9999 for both. LODs for l-arginine and l-citrulline were 0.0462μmol/L and 0.0195μmol/L, respectively, while LOQs were 0.530μmol/L and 0.417μmol/L, respectively. Intra- and inter-day CVs were less than 3.5% and 7.5% in serum, respectively. The average recovery was from 85.5% to 116.5% in serum. Intra-assay CVs were 3.8% and 10.3%, and inter-assay CVs were 13.7% and 10.7% for l-arginine and l-citrulline respectively in tissue. The average recovery was from 92.8% to 113.5% in tissue. This is a reliable and convenient analytical method which is suitable for most clinical laboratories.