Determination of the nitrogen content of nitrocellulose by capillary electrophoresis after alkaline denitration

Nitrocellulose (NC) is a nitrate cellulose ester polymer whose nitrogen content determines its physical and chemical properties and its industrial applications. For the first time, capillary electrophoresis (CE) was used to quantify nitrite and nitrate ions released after the alkaline hydrolysis of NC to determine its nitrogen content. This article focuses on the development and validation of the CE method adapted to the determination of these anions in basic matrices in 3 min total runtime. Molybdate anion was used as internal standard. The matrix effect in sodium hydroxide solution was statistically studied, demonstrating that no significant effect occurred in 0.5 M sodium hydroxide solution. RSDs on normalized migration times (n=20) were 0.05% for both anions, while RSDs on normalized corrected areas (n=20) were 0.8% and 0.7% for nitrite and nitrate ions, respectively. The selectivity of the CE method was checked in the presence of 10 other anionic species potentially present in post-blast residues. Excellent linearities for normalized corrected areas (R2>0.999, residual standard deviations of ca 0.05) were obtained for both anions in the range 5–100 mg L−1. Finally, the optimized CE method was successfully applied to calculate the denitration yields of two NC standards belonging to the non-explosive and explosive classes, and to determine the nitrogen content of a NC contained in a single-base gunpowder. CE, with its speed, low running costs, and simplicity of use, appears as a valuable alternative to ion chromatography for the nitrogen content determination of pure NCs and NC-based explosives, and more generally, for the determination of nitrite and nitrate ions in other highly alkaline matrices.