Low-Level Quantification of tert-Butyl Nitrite in a Pharmaceutical Intermediate

A sensitive, reliable, and reproducible headspace gas chromatography-flame ionization detection method was developed and validated to detect and quantify low levels of tert-butyl nitrite (TBN). TBN is a reagent commonly used by synthetic chemists for nitrogen insertion reactions and is also a potential mutagenic impurity due to a structurally alerting nitrite group. However, there is an inherent analytical challenge in the quantification of TBN due to its chemical instability in solution (e.g., degradation of TBN to tert-butyl alcohol, TBA, in protic solvents). The proposed methodology is based on stabilizing TBN in solution by adding imidazole to a sample diluent before static headspace gas chromatographic analysis. The gas chromatography method utilizes a high-polarity poly(ethylene glycol) stationary phase that provides the resolution of TBN from an interference peak in the sample matrix and facilitates the attainment of the required sensitivity of the TBN peak. The limit of detection (LOD) and limit of quantitation (LOQ) of this method were established as 0.05 mu g mL(-1) (0.05 ppm) and 0.15 mu g mL(-1) (0.15 ppm), respectively. Method validation experiments indicated excellent analytical performance of the method with respect to specificity (resolution of similar to 2.2 from a matrix interference peak), linearity (range: 16.7-1000% of the working concentration), precision (relative standard deviation, RSD, of 1.0% for n = 6 at LOQ level), and recovery (94% at LOQ level). This is the first report of a practical strategy to stabilize TBN for its trace-level quantification.