Sensitivity enhancement in the spectrophotometric determination of silicate by a flotation-exchange-extraction method using an ion associate

Abstract

A flotation-exchange-extraction method for sensitivity enhancement in spectrophotometry is proposed. The concept of the proposed method can be applied to various systems in which an ion associate can float on the interface between an aqueous and an organic phase. The method consists of three main steps: the flotation of an ion associate formed between an analyte and a dye ion (D₁), the exchange of the analyte ion for another dye ion (D₂) and the extraction of the ion associate (D₁.D₂), where D₁ and D₂ are counter ions to each other. The proposed concept has been applied to the determination of silicate. The molar absorptivity and the absorbance of the reagent blank were 7.6 × 10⁵ l mol^–1 cm^–1 and 0.023 at 620 nm, respectively, when D₁ and D₂ were Malachite Green and tetrabromophenolphthalein ethyl ester. The standard deviation (SD) and relative standard deviation (RSD) for ten measurements of 4 × 10^–7M silicate solution were 0.004A and 1.1%, respectively. The SD and RSD for the reagent blank were 0.003A and 10.3%, respectively. The detection limit for silicate is about 5 × 10^–9M or 0.15 p.p.b.