Pralidoxime Chloride Stability-Indicating Assay and Analysis of Solution Samples Stored at Room Temperature for Ten Years

A high-performance liquid chromatographic (HPLC) method is described for quantitation of pralidoxime chloride and its decomposition products 2-carboxy-,2-formyl-, and 2-(aminocarbonyl)-1-methylpyridinium chloride. These decomposition products and 2-cyano- and 2-(hydroxymethyl)-1-methylpyridinium chloride and 1-methyl-2(1H)-pyridinone were separated from pralidoxime chloride on a silica gel column using a mobile phase of acetonitrile:water (86:14) in which the aqueous component was 8.36 mM in tetraethylammonium chloride and 52.5 mM in acetic acid. This method allows quantitation of the relatively low levels of 2-formyl-1-methylpyridinium chloride formed in acidic solution at room temperature. Sensitivity was shown to be at least 5 ng of the pralidoxime chloride and 15 ng of the 2-carboxy-,2-formyl-, and 2-(aminocarbonyl)-1-methylpyridinium chloride injected on column. The coefficient of variation was 4% or less for all components measured. Autoinjectors containing 300 mg/mL of pralidoxime chloride in water were stored at room temperature for 8–10 years, followed by analysis for hydrogen cyanide using an ion-selective electrode. Less than 15 μg of cyanide per autoinjector was detected. The HPLC analysis of the solutions after being stored an additional 3–4 years at ∼5°C demonstrated that > 90% of the total of all measured components consisted of pralidoxime chloride. The remaining percentage was made up of 2-carboxy-,2-formyl-, and 2-(aminocarbonyl)-1-methylpyridinium chloride.