Ultraperformance LP-MS/MS chromatograms obtained from urine samples or standards. A: chromatogram obtained from urine samples examined using the selected reaction monitoring (SRM) mass transition tuned for 2′,3′-cGMP and 3′,5′-cGMP (346 → 152 m/z). B: chromatogram obtained from urine samples examined using the SRM mass transition tuned for 5′-GMP, 3′-GMP, and 2′-GMP (364 → 152 m/z). C: chromatogram obtained by UPLC-MS/MS analysis of a standard solution containing authentic 2′,3′-cGMP and 3′,5′-cGMP. D: chromatogram obtained by ultraperformance LC-MS/MS analysis of a standard solution containing authentic 5′-GMP, 3′-GMP, and 2′-GMP. Retention times were as follows: 2.60 and 3.70 min for 2′,3′-cGMP and 3′,5′-cGMP, respectively (A); 1.84, 2.21, and 3.45 min for 5′-GMP, 3′-GMP, and 2′-GMP, respectively (B); 2.67 and 3.80 min for 2′,3′-cGMP and 3′,5′-cGMP, respectively (C); and 1.82, 2.16, and 3.40 min for 5′-GMP, 3′-GMP, and 2′-GMP, respectively (D).