2.3. Liquid chromatography with mass spectrometry
A Hewlett-Packard (Palo Alto, CA, USA) HP 1100 Series LC–MS system equipped with a binary solvent pump, an autosampler, and a mass-selective detector coupled with an analytical work station was employed. The mass-selective detector consisted of a standard atmospheric pressure ionization (API) source configured as APCI. Typical operating conditions of the APCI interface in the negative mode were: vaporizer temperature, 450 8C; nebulizer gas,nitrogen at a pressure of 60 p.s.i. (1 p.s.i.56894.76Pa); drying gas, also nitrogen, at a flow-rate of 4 l
21 min and temperature of 350 8C; capillary voltage,4000 V; and corona current 25 mA
Full-scan LC–MS chromatograms were obtained by scanning from m/z 100 to 400. Time-scheduled selected-ion monitoring (SIM) of the most abundant ion of each compound was used for quantification.