Identification of losartan degradates in stressed tablets by LC-MS and LC-MS/MS.

Three unknown peaks were observed in the severely stressed losartan tablets (at 40 degrees C and 75% relative humidity for 3 years) analyzed by a stability indicating HPLC method. The sample solutions were subjected to liquid chromatography-tandem mass spectrometric (LC-MS/MS) analysis to obtain the chemical identities of these potential degradates. High accuracy and sensitivity of losartan and its degradates were obtained by using atmospheric pressure chemical ionization (APCI) technique in the LC-MS/MS analysis. Three trace level degradates (< or = 0.1%) were found to be the aldehyde and dimeric derivatives of losartan. The structural assignment was further confirmed by comparing the tandem mass spectra of the unknowns with those of the authentic materials of each corresponding degradate. Finally, the mechanistic pathways for the formation of the dimers are discussed.