Determination of phosphate in water by means of a new electrochemiluminescence technique based on the combination of liquid-liquid extraction with benzene-modified carbon paste electrode

In this paper, it was found that the hydrophobic ion-associated complex of the molybdophosphoric heteropoly acid with protonated butyl-rhodamine B (BRhB) could be formed and was further selectively extracted into the bulk of the paraffin oil-based carbon paste electrode (CPE). At the same time, compared with other modifiers, the benzene-modified CPE created a suitable electrochemiluminescence (ECL) reaction microenvironment for electro-oxidation BRhB to produce the stronger ECL signal when a 1.30 V electrolytic potential was applied to the CPE in the alkaline medium. Based on these findings, a selective and sensitive ECL method for indirectly detecting phosphate was developed. Under the optimum experimental conditions, the ECL intensity was linear with the concentration of phosphate in the range of 2.0 × 10⁻¹⁰ to 1.0 × 10⁻⁸ g mL⁻¹. The detection limit was 8.0 × 10⁻¹¹ g mL⁻¹. The proposed method has been applied successfully to the analysis of phosphate in the water samples.