Analysis of polynitrophenols and hexyl by liquid chromatography–mass spectrometry using atmospheric pressure ionisation methods and a volatile ion-pairing reagent

An LC–MS method for the determination of picric acid (2,4,6-trinitrophenol), its reductive transformation products picramic acid (2-amino-4,6-dinitrophenol) and iso-picramic acid (4-amino-2,6-dinitrophenol) and hexyl (2,2′,4,4′,6,6′-hexanitrodiphenylamine) has been developed. The analytes were separated using ion-pairing chromatography with a volatile ion-pairing reagent suitable for subsequent MS detection. The performance of an atmospheric pressure chemical ionisation (APCI) and an electrospray ionisation (ESI) interface was compared. ESI-MS is more sensitive for the analytes, especially for hexyl and picric acid, APCI-MS delivered more fragments necessary for unequivocal identification. With LC–ESI-MS limits of detection using single ion monitoring (SIM) mode are 4 ng (iso-picramic acid), 800 pg (picramic acid), 400 pg (picric acid) and 80 pg (hexyl). For quantification, 15N-picric acid was used as an internal standard. Using this new method, the degradation of picric acid in soil was monitored in a laboratory study. Furthermore, the presence of picramic acid was for the first time verified in soil samples from a former ammunition plant.