Determination of nitrite and nitrate in postmortem whole blood samples of 10 sodium nitrite poisoning cases: The importance of nitrate in determining nitrite poisoning.

Sodium nitrite (NaNO), a widely used food preservative, has become a popular agent in South Korea for use in committing suicide since the mid-2010s because of its easy access. After ingesting sodium nitrite, nitrite ions oxidize hemoglobin to methemoglobin in red blood cells (RBCs), causing methemoglobinemia which can be fatal depending on the severity. As the number of deaths involving sodium nitrite has increased rapidly over the years, we developed a quantitative analysis method for nitrite and its oxidized form, nitrate, using ion chromatography (IC) with a conductivity detector. A simple ultrafiltration method was used for sample preparation because chloride ions which usually interfere with nitrite in most IC methods were completely separable using the developed analytical method. The limit of detection and lower limit of quantitation of nitrite were 0.5 and 1 mg/L, respectively. Nitrite and nitrate showed good linearity in the range of 1-500 mg/L and 5-500 mg/L, respectively. The established method was successfully applied to 10 authentic sodium nitrite poisoning cases, resulting in low nitrite concentrations (32.4 ± 29.5 mg/L in peripheral blood samples and 20.4 ± 18.7 mg/L in heart blood samples) and high nitrate concentrations (298.0 ± 25.6 mg/L in peripheral blood samples and 252.0 ± 41.3 mg/L in heart blood samples). The imbalance between nitrite and nitrate was due to the extensive conversion of nitrite to nitrate in postmortem bloods, which was confirmed by spiking nitrite into blank blood samples. In conclusion, not only the blood concentrations of nitrite but also those of nitrate should be quantified and considered for the determination of sodium nitrite poisoning, especially in postmortem blood samples.