Capillary electrophoresis-electrospray mass spectra of the herbicides paraquat and diquat

✍ Scribed by Xinbei Song; William L. Budde

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 607 KB
• Volume: 7
• Category: Article
• ISSN: 1044-0305
• DOI: 10.1016/1044-0305(96)00070-0

✦ Synopsis

The positive ion electrospray mass spectra of the quatemary ammonium salt herbicides paraquat and diquat are examined by on-line separation with capillary electrophoresis (CE) and by direct infusion of the analytes. The analytes are separated by CE in 7-10 min at pH 3.9 in 50% methanol-water by using several different separation buffer electrolytes. The capillary electrophoresis-electrospray ionization (CE-ES) mass spectra of paraquat and diquat consist primarily of doubly charged molecular ions, singly charged molecular'ions, and singly charged deprotonated ions. The direct infusion spectra consist primarily of doubly charged molecular ions and singly charged deprotonated ions. The relative abundances of the doubly charged and deprotonated ions depend strongly on the presence or absence of ammonium ion in the CE separation buffer or the direct infusion solution. A deprotonation mechanism is proposed in which the free base ammonia is the deprotonating agent in the desolvating charged droplets or in the gas phase. The analytical potential of the CE-ES electrospray approach for environmental analyses is evaluated in terms of the precision of replicate injections, linear concentration range, and estimated detection limit. (1 Am Sot Mass Spectrom 1996, 7, 982-986) P araquat and diquat are herbicides used to produce desiccation and defoliation on contact. Paraquat (l,l'-dimethyl-4,4'-bipyridinium dichloride) and diquat [6,7-dihydrodipyrido(1,2a:2'1'-c)pyrazinedium dibromide] have been used in large quantities in the United States to control terrestrial and aquatic weeds. The compounds have similar structures; each has two quatemary nitrogens. In the United States the maximum contaminant level for diquat in drinking water is 20 pg/L. Paraquat currently is not regulated in drinking water, but its use is restricted in the United States.