Ionization of dichlorophenols for their analysis by capillary electrophoresis–mass spectrometry

In order to develop an advanced analytical method using capillary electrophoresis (CE) for non-volatile environmental pollutants such as endocrine disruptors, combination with mass spectrometry (MS) is necessary for their identification. We chose dichlorophenols (DCPs) as test samples because one of their isomers, 2,4-DCP, is suspected to have endocrine disrupting effects. A preliminary study on their separation by CE–MS was performed using a laboratory-made electrospray ionization (ESI) interface. For the effective ionization of 2,4-DCP at the ESI interface, applied voltage, assisted nitrogen-gas flow-rate, salts and their concentration, and organic solvents in the sample matrix were optimized according to the signal intensity. The intensity of other DCPs under the same conditions, however, was quite different. We tried to modify the atmospheric chemical pressure ionization (APCI) interface in order to reduce the flow-rate. The intensity of directly injected DCPs was not so different from one another using the modified prototype APCI interface.