As a substance present in organisms, nitrite is a metabolite of nitric oxide and can also be ingested. Nitrate is the metabolite of nitrite. Therefore, it is necessary to measure it quickly, easily and accurately to evaluate the health status of humans. Although there have been several reviews on analytical methods for non-biological samples, there have been no reviews focused on both sample preparation and analytical methods for biological samples. First, rapid and accurate nitrite measurement has significant effects on human health. Second, the detection of nitrite in biological samples is problematic due to its very low concentration and matrix interferences. Therefore, the pretreatment plus measuring methods for nitrite and nitrate obtained from biological samples since 2010 are summarized in the present review, and their prospects for the future are proposed. The treatment methods include liquid–liquid microextraction, various derivatization reactions, liquid–liquid extraction, protein precipitation, solid phase extraction, and cloud point extraction. Analytical methods include spectroscopic methods, paper-based analytical devices, ion chromatography, liquid chromatography, gas chromatography–mass spectrometry, electrochemical methods, liquid chromatography–mass spectrometry and capillary electrophoresis. Derivatization reagents with rapid quantitative reactions and advanced extraction methods with high enrichment efficiency are also included. Nitrate and nitrate should be determined at the same time by the same analytical method. In addition, much exploration has been performed on formulating fast testing through microfluidic technology. In this review, the newest developments in nitrite and nitrate processing are a focus in addition to novel techniques employed in such analyses.

Acute liver injury (ALI) is a significant global public health issue that can rapidly develop into acute liver failure, seriously endangering the safety of patients. Eugenol has various pharmacological effects such as antioxidant, anti-inflammatory, antibacterial, and neuroprotective properties. Through pathological section observation, eugenol can alleviate the degree of liver damage caused by thioacetamide. Based on metabolomics, a total of 87 metabolites were found to have differences in content between the control group and the thioacetamide group. Compared with the control group, the contents of 42 metabolites had increased and 45 metabolites had decreased in the thioacetamide group. These differential expressed metabolites mainly indicate inflammatory damage, oxidative damage, and abnormal energy metabolism. There were 269 metabolites with differences in content between the eugenol intervention group and the thioacetamide group. Compared with the thioacetamide group, there were 101 metabolites with increased content and 168 metabolites with decreased content in the eugenol intervention group. These differential expressed metabolites suggest that eugenol intervention can correct inflammation damage, oxidative damage, and energy metabolism abnormalities caused by TAA. This study found through pathological section observation and metabolomics that eugenol has a protective effect on acute liver injury caused by thioacetamide, and the protective mechanism may be related to the antioxidant and anti-inflammatory effects of eugenol.