An LC-MS method for the detn. 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) was developed. The analytes were sepd. using ion-pairing chromatog. with a volatile ion-pairing reagent suitable for subsequent MS detection. The performance of an atm. pressure chem. ionization (APCI) and an electrospray ionization (ESI) interface was compared. ESI-MS is more sensitive for the analytes, esp. 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 std. Using this new method, the degrdn. of picric acid in soil was monitored in a lab. study. Also, the presence of picramic acid was for the 1st time verified in soil samples from a former ammunition plant.