Suicide by sodium nitrite–an emerging trend

Abstract

Suicide by sodium nitrite ingestion is increasingly being reported in many parts of the world due to the ease of access of information and material via the internet. Our laboratory received our first case of suspected nitrite fatality in October 2021, and soon after, a second case in November 2021. Both deceased were found dead at their home with packet/bottle of sodium nitrite present in their rooms. The deceased in the first case was a 29-year-old female and the specimens submitted for toxicology analyses were peripheral blood, bile, vitreous humour and gastric contents. The second case was a 16-year-old male and his peripheral blood and urine were submitted for toxicology analyses. To prove nitrite consumption, a relatively simple colorimetric method using commercially available Griess reagent was evaluated in the vitreous humour and gastric contents in case 1 and urine in case 2. The Griess assay was adopted from the work of Tomsia M. et. al (J. Forensic. Leg. Med., 2021, 102186). It involves the reaction between N-(1-naphtyl)ethylenediamine dichloride and nitrite to form a diazonium salt which further react with sulphanilamide contained in the Griess reagent to produce a purple coloured azo compound. The colour of the azo compound increases proportionally with nitrite concentration and can be measured by a UV-Vis spectrophotometer at around 548 nm. For quantitation, calibration curves from 0.5 to 10 μg/ml nitrite were prepared in the respective matrices (vitreous humour, urine and water for gastric contents). To further confirm the presence of nitrite in these specimens, a complementary technique by GC/MS using pentafluorobenzyl bromide (PFB-Br) derivatization is employed (Tsikas D., J. Chromatogr. B, 2016, 1043:187-201). Nitrite levels determined by Griess assay were found to be 78 μg/ml in the vitreous humour and 32 mg/ml in the gastric contents of case 1, and 13.9 μg/ml in the urine of case 2. These levels were comparable to those reported by Tomsia M et. al. The nitrite levels in the vitreous humour and urine were also far above the typical endogenous nitrite levels (around 0.01–0.3 μg/ml in vitreous humour and 0.01–0.05 μg/ml in urine). The presence of nitrite as α-nitro-pentafluorotoluene was also confirmed in the 3 specimens by GC/MS. Nitrate does not interfere in both the Griess assay and GC/MS method. Blood nitrite levels in nitrite poisoning cases were often present at levels not significantly different from that of endogenous levels as it is rapidly oxidized to nitrate by haemoglobin. For this reason, blood nitrate levels were determined instead in some of the reported nitrite ingestion cases. However, the determination of nitrite in the deceased's specimen is still preferred as a direct correlation to the substance of poisoning. In this aspect, vitreous humour is a useful specimen as it is relatively clean and the easiest to process. This case study presented the use of Griess reagent and PFB-Br derivation with GC/MS analysis for the quantitation and confirmation of nitrite in vitreous humour, gastric contents and urine specimens of nitrite ingestion cases. The approach is simple and employs relatively inexpensive reagents and instruments that are readily available in most toxicology laboratories.