A new ion-pair ultrasound assisted-cloud point extraction approach for determination of trace V(V) and V(IV) in edible vegetal oils and vinegar by spectrophotometry

Abstract

A new ion-pair ultrasound-assisted-cloud point extraction (UA-CPE) procedure for the preconcentration and determination of V(V) and V(IV) in edible vegetal oils and vinegar by spectrophotometry at 530 nm was developed. The method is based on selective and sensitive anionic chelation of V(V) and V(IV) with EDTA, and then a stable ion-pair formation of the formed chelate complexes with cationic phenazine dye, Safranin T, at pH 4.0 and/or pH 5.0 respectively, which can be easily extracted into the micellar phase of Triton X-114 with the help of ultrasound energy. The variables affecting ion-pair formation and extraction efficiency were evaluated and optimized. Under the optimized conditions, there was a linear relationship in range of 1–40 μg/L for V(IV) at pH 5.0 with higher calibration sensitivity while it obtained a rectilinear behavior in the range of 2–180 μg/L for V(V) at pH 4.0. The limits of detection and quantification for V(IV) were 0.26 and 0.85 μg/L with a sensitivity enhancement of 83.6 from preconcentration of 35-mL sample, respectively where these values are 0.53 and 1.77 μg/L, respectively, for V(V). The recovery rate and precision for five replicate measurements of 5, 25 and 100 μg/L V(V) and V(IV) were in range of 98–101%, 3.1–4.2% and 3.2–4.5%, respectively. The accuracy was statistically verified by analysis of a certified oil sample with both the developed method and independent comparison method, and the method was successfully applied to the analysis of total V contents of edible vegetal oils and vinegar samples after preconcentration.