UC San Diego

Sodium azide is a toxic substance that has a high potential for abuse and is used in multiple industries ranging from laboratories to farms to automobile factories. The potentially deadly toxic has multiple routes of absorption, which make a fast and effective detection method extremely important. We developed a dynamic method of detection by observing the spectral changes when sodium azide binds to cobinamide, a vitamin B₁₂ analogue. The K/a of sodium azide binding to cobinamide was found to be 6.10 x 10⁻⁵ 1/M. The detection limit and quantification limit of the cobinamide-based method performed in phosphate buffer were 180 nM and 580 nM respectively. The method was sensitive and accurate enough to detect sodium azide at a concentration of 25 µM in blood samples. The absorbance values change upon addition of sodium azide in the 300 nm to 600 nm range. At 420 nm, the absorbance values increases linearly upon addition of sodium azide and decreases linearly at 491 nm upon increasing addition of sodium azide. The 420 nm:491 nm wavelength ratio was chosen for accuracy and sensitivity. Our method has a lower detection limit and quantification limit when compared to the micro-diffusion assays described in literature. Although the cobinamide based method is less sensitive than ion chromatography or gas chromatography methods, the assay described in this paper has a potential higher throughput, is easier to process, and is sensitive enough to detect potentially toxic concentrations in biological samples. In this paper we describe a facile method of detecting the deadly chemical, sodium azide