Deaths related to nitrogen inhalation: Analytical challenges

Dinitrogen (N₂) has been increasingly connected to suicidal deaths. The analysis of N₂ in post-mortem cases still represents a major challenge in forensic toxicology and circumstantial data has so far played a major role for the determination of the cause of death. In this paper, after presenting a review of cases of N₂ intoxication described in forensic literature, we report the application of two approaches in order to quantify an excess of N₂ in post-mortem whole blood collected from a case of suicide by nitrogen inhalation. N₂ analyses were performed by GC-MS on the suicidal case and on controls taken from 10 autopsy cases with similar PMI (5 traumatic deaths and 5 deaths by asphyxia). The percentage of N₂ was estimated by building a five-point N₂ peak area calibration curve (0, 15.6 %, 62.4 % 78.1 %, 100 %) and through an external QC, assessing linearity, accuracy and precision, LLOQ, specificity and stability of N₂ in the sample vial. Percentage of N₂ of the case was significantly higher than the post-mortem controls (p<0.05). The N₂/O₂ ratio of the case and controls was also calculated as an additional indicator, and was significantly higher in the case (p<0.05). The strengths and the limitation of both methods are reported in the paper. Toxicological confirmation for N₂ are rarely performed when the cause of death is evident, probably due to the lack of validated methods and the complexity of the interpretation of N₂ concentration in biological fluids. The presented methods can be rapidly and profitably applied with instrumentation normally available in forensic laboratories.