The chromatograph employed for the separation was a Dionex HPLC instrument (Sunnyvale, CA, USA) equipped with the following modules: ASI-100 automatic autoinjector; P680 HPLC pump; TCC-100 heating column; RF 2000 fluorescence detector; and UCI-50 universal chromatographic interface. The Chromeleon 6.60 software was used. The chromatographic separation was carried out using a Chromolith Performance RP-18e (100mm×4.6 mm) monolithic column (Merck).