Nanogold-actuated biomimetic peroxidase for sensitized electrochemical immunoassay of carcinoembryonic antigen in human serum

We present a method for the simultaneous determination of guanidinosuccinic acid (GSA) and guanidinoacetic acid (GAA) from urine by protein precipitation and liquid chromatography/tandem mass spectrometry. The chromatographic separation was performed using a cation exchange column with an elution gradient of 0.1 mM and 20 mM ammonium acetate buffers. GSA was detected with the mass spectrometer in negative ion mode monitoring at m/z 174.1, and GAA, creatinine, arginine, and homoarginine were in positive ion mode monitoring at m/z 118.1, 114.1, 175.1, and 189.1, respectively. As an internal standard, l-arginine-¹³C₆ hydrochloride and creatinine-d₃ (methyl-d₃) were used. The calibration ranges were 0.50-25.0 μg mL⁻¹, and good linearities were obtained for all compounds (r > 0.999). The intra- and inter-assay accuracies (expressed as recoveries) and precisions at three concentration levels (1.00, 5.00 and 25.0 μg mL⁻¹) were better than 83.8% and 7.41%, respectively. The analytical performance of the method was evaluated by determination of the compounds in urine from male C57BL/J Iar db/db diabetes mellitus (DM) mice. The values of GSA and GAA corrected by the ratios of the individual compounds to creatinine were significantly increased in DM mice compared with control mice. These results indicated that the newly developed method was useful for determining urinary guanidino compounds and metabolites of arginine.