Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry: A Strategy for Optimization, Characterization, and Quantification of Antioxidant Nitro Derivatives

As an antioxidant, N-phenyl-beta-naphthylamine (PBNA) inhibits the activity of oxidants, such as NOx, to prevent the degradation of energetic materials. In the presence of NOx, nitrated products can be generated in the process potentially. To characterize nitrated PBNA in a nontargeted analysis of complex samples as such, liquid chromatography tandem quadrupole time-of-flight (LC-QTOF), as an excellent analytic technique, is used due to its high resolution and sensitivity. However, a systematic approach of instrumentation optimization, data interpretation, and quantitative determination of products is needed. Through a step-by-step evaluation of the instrumental parameters used in the QO, Q1, and Q2 compartments of LC-QTOF, optimal ion yields of precursor ions and high-resolution MS2 fragmentation spectra at low mass defects were obtained in both negative and positive electrospray ionization modes. Through rationalization of the fragmentation pathways and verification using theoretical masses, the mononitro derivative of PBNA was accurately identified as N-(4-nitrophenyl)-naphthalen-2-amine and further confirmed using a reference standard. Using strict criteria provided by the analytical guidelines (e.g., SANTE), limit of quantitation, limit of detection, and calibration were established for the quantitation of PBNA and nitrated PBNA. From optimization to characterization and subsequent quantification of the mononitro-PBNA derivative, for the first time, the applicability of this strategy is demonstrated in the aged energetic binders.

Automated summary

This study investigated the analysis of N-phenyl-beta-naphthylamine (PBNA) using liquid chromatography tandem quadrupole time-of-flight (LC-QTOF) and successfully identified and quantified the nitrated products of PBNA. The instrumental parameters were optimized to obtain accurate results, and the fragmentation pathways were rationalized and validated using reference standards.