Sodium nitrite intoxications: Quantification of nitrite and nitrate levels in postmortem blood

In recent years, nitrite (salt) overdose has become a method of suicide worldwide. This study presents the development and validation of a high-performance liquid chromatography with diode array detection (HPLC-DAD) method for the quantification of nitrite and nitrate in postmortem whole blood. Nitrate measurements were performed after precipitation, filtration, and matrix-clean up. Potassium ferricyanide was used to stabilize nitrite and prevent degradation processes, while the Griess reaction allowed sensitive nitrite quantification. In eleven cases of suspected sodium nitrite intoxication, nitrite concentrations ranged from 1.0 to 529 µg/mL in femoral blood and 1.3-176 µg/mL in heart blood, while nitrate concentrations ranged from 57 to 997 µg/mL and 54-907 µg/mL, respectively. Physiological nitrate concentrations of max. 72 µg/mL were determined in postmortem blood (n = 5), whereas physiological nitrite levels were not detectable (LOD/LOQ: 1 µg/mL). Significant inter-case variability was observed in nitrate and nitrite levels, reflecting the influence of individual postmortem biochemistry, condition, and presumably thanatomicrobial profile and activity, while intra-case discrepancies between femoral and heart blood highlight the importance of analyzing multiple matrices. Nevertheless, an intoxication with sodium nitrite was either concluded if: (i) Nitrite was detected (10/11) or (ii) High nitrate concentrations (above physiological level) were measured (1/11). The interpretation of cases was supported by toxicological data like methemoglobin levels, circumstantial evidence, and morphological findings such as grey skin coloration and chocolate-brown colored blood. The findings enhance the understanding of highly variable nitrate and nitrite dynamics in postmortem toxicology and provide practical insights for forensic investigations, emphasizing the integration of analytical methods, circumstantial, and morphological evidence.