An established spectrophotometric method was employed to determine the concentration of sodium azide. It was found that this method could only be used with a good accuracy (to within ±0.3%) under the following conditions: the solution of cerium(IV) ammonium nitrate, which was prepared using analytical-reagent grade materials without further purification and used to react with sodium azide, must be either freshly prepared or kept in a refrigerator (if the solution was kept at room temperature its concentration must be checked and re-determined prior to azide determination); and the cerium(IV) ammonium nitrate solution should be brought up to room temperature before taking the measurements.