Sensitive determination of quaternary ammonium salts by extraction-spectrophotometry of ion associates with bromophenol blue anion and coextraction

Abstract

The chloroform extraction behaviour of the ion-associates of a Bromophenol Blue anion (BPB 2− :blue) with quaternary ammonium cations (Q +) was examined. During extraction using Q + with a small number of carbon atoms (Nc) or using Q + with a large Nc and high concentrations of BPB 2−, the addition of a proton to BPB 2− gives HBPB − (yellow), which can be extracted as the 1:1 ion-associate Q + ·HBPB − ( ϵ = 2.5 × 10 4 1 mol −1 cm −1 at λ max = 416 nm) with Q + into chloroform. At high BPB 2− concentrations, the extraction level of the 1:2 ion-associate of one Q +, (Q +) 2 ·BPB 2− ( ϵ = 9.4 × 10 4 1 mol −1 cm −1 at λ max = 608 nm) was elevated by the presence of other Q + and the sensitivity and the selectivity for Q + determination was increased by using co-extraction and a wavelength of 608 nm.