Capillary electrophoresis time-of-flight mass spectrometry of paraquat and diquat herbicides

Capillary electrophoresis (CE) and mass spectrometry (MS) were investigated for the analysis of paraquat and diquat herbicides. The mass spectrometer was a home-built time-of-flight instrument (TOFMS) equipped with an electrospray ionization (ESI) source. A coaxial liquid sheath ESI source was utilized for interfacing the CE to the TOFMS, and mass spectra were acquired with both liquid sheath and microspray sources. The ESI-TOF spectra of paraquat and diquat were dependent on the background electrolyte composition; singly or doubly charged ions were displayed preferentially. Volatile buffer systems, compatible with the ESI-MS, were used in mixed aqueous/organic solvents. By using the sample stacking technique at the CE injection port, low femtomole detection was achieved from 5 μM solutions.