Determination of diquat and paraquat in water by liquid chromatography/electrospray-mass spectrometry using volatile ion-pairing reagents

A method for the determination of the herbicides paraquat and diquat in wat er was developed using liquid-chromatography/electrospray ionization-mass s pectrometry (LC/ESI-MS). This method did not include any sample-concentrati on steps. Only 0.1 M nonafluoropentanoic acid (NFPA) was added to the filte red sample. An aliquot (200 mu L) of this sample was analyzed by reversed-p hase liquid chromatography with the postcolumn addition of 2-propanol follo wed by ESI-MS. Paraquat and diquat were detected using the [M2(+)-H+] ion a t m/z 185 and 183, respectively. Quantification was performed by an externa l standard method. The detection limits were 0.1 ng/mL (paraquat) and 0.2 n g/mL (diquat). The repeatability and reproducibility were 2.1% and 7.4% for paraquat and 2.7% and 8.1% for diquat.