Identification of Cationic Herbicides in Deionized Water,Municipal Tap Water,and River Water by Capillary Isotachophoresis/On-Line Raman Spectroscopy

Abstract

Isotachophoresis (ITP), coupled with Raman spectroscopic detection, is used to separate and identify two cationic herbicides, paraquat and diquat, in spiked deionized water, municipal drinking water, and river water samples. On-line preconcentration is achieved with the use of field-amplified injection into a 0.03–0.1 M H₂SO₄ or Na₂SO₄ leading electrolyte solution, and isotachophoresis is achieved with the use of a 0.03–0.1 M tris(hydroxymethyl)—aminomethane (Tris) trailing electrolyte solution. The herbicides are concentrated to above 10⁻³ M at the detection window, allowing measurement of Raman spectra with 1-s integration windows. Spectra of the herbicides are obtained from solutions at initial concentrations in deionized water at 3.5 × 10⁻⁷ M (90 ppb) paraquat/5.8 × 10⁻⁸ M (20 ppb) diquat, from drinking water initially at 1.3 × 10⁻⁶ M (335 ppb) paraquat/1.0 × 10⁻⁶ M (360 ppb) diquat, and river water initially at 5.0 × 10⁻⁶ M (1.3 ppm) paraquat and 3.0 × 10⁻⁶ M (1.0 ppm) diquat. The utility of correlation to identify the presence of analytes and of factor analysis to recover spectra from solutions at low initial concentrations of the herbicides is demonstrated.