Ion chromatographic method for determination of oxyanions in solutions equilibrated with soils

Abstract

Methods based on simultaneous determination of oxyanions in soil solution are needed for studies of competitive adsorption of several oxyanions by soils. An accurate and precise ion Chromatographie (IC) method was developed for simultaneous determination of PO₄ ³‐, AsO₄ ³% SeO₄ ^2‐, WO₄ ^2‐, and MoO₄ ^2‐ in solution equilibrated with soil. The water extract obtained was analyzed by a Dionex 2002i IC after filtering (0.45‐μm membrane filter). The IC unit was fitted with a guard column (AG‐3), a separator column (AS‐3), a 50‐μL injection loop, and a micromembrane suppressor system eluted with 12.5 mM H₂SO₄. A solution made 3.0 mM NaHCO₃ + 6.0 mM Na₂CO₃ was used as an eluant, and conductivity was used as the mode of detection. The proposed method was tested by analyzing soil extracts obtained after equilibrating soils with a series of solutions containing mixtures of these oxyanions. Results showed that the elution times for PO₄ ^3‐, AsO₄ ^3‐, SeO₄ ^2‐, WO₄ ^2‐, and MoO₄ ^2‐ were 1.8, 2.5, 4.1, 6.6, and 8.0 min, respectively. The accuracy of the method was evaluated by spiking the soil extracts with standard solution of the oxyanions. The recovery of standards (made to correspond to 0.5 mM) added to the solution analyzed ranged from 95.4% to 104.6%, with coefficients of variation ranging from 0% to 10.5%. The detection limits of oxyanions studied ranged from 1 μM with PO₄ ^3‐ to 25 (μM with MoO₄ ^2‐. A single operator can analyze about 50 solutions of the five oxyanions in a normal working day.