The ESI-MS system was calibrated using sodium formate clusters introduced by loop-injection at the beginning of the LC–MS run. The LC–MS data was processed using Data Analysis 4.1 software (Bruker Daltonik, Bremen, Germany). Molecular ions[M+H]+ were extracted from full scan chromatograms and peak areas were integrated. The extraction window of individual ion chromatograms was }0.05 m/z units. The compounds present in each sample were identified by comparing their retention times with those of standards, and based on molecular mass and structural information from the MS detector.