Nitric oxide (NO) is a short-lived free radical involved in various physiological processes, including blood pressure regulation, immune response, and neural communication. Accurate detection and quantification of NO and its metabolites are crucial for understanding health and disease. Due to NO's short half-life, alternative methods for detecting its reaction products have been developed. The quantification of NO metabolites in biological samples provides insights into in vivo NO production, bioavailability, and metabolism. However, sampling a single compartment like blood or plasma may not accurately reflect whole-body NO status, especially in tissues. Therefore, methods are needed to detect and quantify NO and its products in multiple compartments of experimental animals. NO is metabolized through oxidation to nitrite (NO₂⁻) and nitrate (NO₃⁻). The oxidation of NO by molecular oxygen is a second-order reaction. NO and nitrite are rapidly oxidized to nitrate in whole blood. The half-life of NO₂⁻ in human blood is about 110 seconds, while nitrate has a longer half-life of 5-8 hours. NO can also react with superoxide to form peroxynitrite (ONOO⁻), a potent oxidant. The presence of 3-nitrotyrosine (3NT) in tissues may indicate ONOO⁻ formation, but 3NT can also be generated through other pathways, making it not a specific marker. Nitrite is a central molecule in NO biology and serves as a signaling molecule. It is found in high abundance in mammalian tissues and is a short-lived ion in circulation. Nitrite can be reduced back to NO under physiological conditions and can directly nitrosate thiols to form S-nitrosothiols (RSNOs). Nitrite and nitrate can also be derived from the diet and contribute to systemic NO production. Sample preparation is critical for accurately quantifying NO metabolites. Extreme care must be taken to preserve NO products and avoid artifact formation during sample preparation. Nitroso/nitrosyl products are unstable and rapidly decompose, so samples must be collected and preserved to maintain their integrity. Blood and tissue samples should be processed quickly to prevent metabolic changes that could alter NO species. The Griess reaction is a common method for detecting NO metabolites, involving the reduction of nitrate to nitrite followed by a diazotization reaction. High-performance liquid chromatography (HPLC) and fluorometric methods are also used for detecting NO metabolites. These methods offer high sensitivity and specificity for quantifying NO and its products in various biological matrices. Fluorometric methods, such as the diamino-naphthalene (DAN) assay and the diaminofluoroscein-2 (DAF-2) assay, are used to detect NO. These methods offer advantages in sensitivity and versatility. However, DAF-2 can be affected by autofluorescence and other factors,Nitric oxide (NO) is a short-lived free radical involved in various physiological processes, including blood pressure regulation, immune response, and neural communication. Accurate detection and quantification of NO and its metabolites are crucial for understanding health and disease. Due to NO's short half-life, alternative methods for detecting its reaction products have been developed. The quantification of NO metabolites in biological samples provides insights into in vivo NO production, bioavailability, and metabolism. However, sampling a single compartment like blood or plasma may not accurately reflect whole-body NO status, especially in tissues. Therefore, methods are needed to detect and quantify NO and its products in multiple compartments of experimental animals. NO is metabolized through oxidation to nitrite (NO₂⁻) and nitrate (NO₃⁻). The oxidation of NO by molecular oxygen is a second-order reaction. NO and nitrite are rapidly oxidized to nitrate in whole blood. The half-life of NO₂⁻ in human blood is about 110 seconds, while nitrate has a longer half-life of 5-8 hours. NO can also react with superoxide to form peroxynitrite (ONOO⁻), a potent oxidant. The presence of 3-nitrotyrosine (3NT) in tissues may indicate ONOO⁻ formation, but 3NT can also be generated through other pathways, making it not a specific marker. Nitrite is a central molecule in NO biology and serves as a signaling molecule. It is found in high abundance in mammalian tissues and is a short-lived ion in circulation. Nitrite can be reduced back to NO under physiological conditions and can directly nitrosate thiols to form S-nitrosothiols (RSNOs). Nitrite and nitrate can also be derived from the diet and contribute to systemic NO production. Sample preparation is critical for accurately quantifying NO metabolites. Extreme care must be taken to preserve NO products and avoid artifact formation during sample preparation. Nitroso/nitrosyl products are unstable and rapidly decompose, so samples must be collected and preserved to maintain their integrity. Blood and tissue samples should be processed quickly to prevent metabolic changes that could alter NO species. The Griess reaction is a common method for detecting NO metabolites, involving the reduction of nitrate to nitrite followed by a diazotization reaction. High-performance liquid chromatography (HPLC) and fluorometric methods are also used for detecting NO metabolites. These methods offer high sensitivity and specificity for quantifying NO and its products in various biological matrices. Fluorometric methods, such as the diamino-naphthalene (DAN) assay and the diaminofluoroscein-2 (DAF-2) assay, are used to detect NO. These methods offer advantages in sensitivity and versatility. However, DAF-2 can be affected by autofluorescence and other factors,