Determination of azide in biological fluids by use of electron paramagnetic resonance

A simple and sensitive method has been developed for the determination of azide ion (N3−) in biological fluids and beverages. The procedure was based on the formation of a ternary complex Cu(N3)2(4-methylpyridine)x in benzene, followed by its detection by electron paramagnetic resonance. The complex in benzene showed a characteristic four-peak hyperfine structure with a g-value of 2.115 at room temperature. Cu2+ reacted with N3− most strongly among common metals found in biological fluids. Several anions and metal ions in biological fluids did not interfere with the determination of N3− in the presence of large amounts of Cu2+ and oxidants. In the present method, N3− at the concentration from 5 μM to 2 mM in 100 μl solution could be determined with the detection limit of 20 ng. The recoveries were more than 95% for N3− added to 100 μl of blood, urine, milk and beverages at 200 μM. Our method is recommendable because it takes less than 10 min to determine N3− and the produced complex is quite stable.