Selective determination of sparteine by thermochromism of associates with tetrabromophenolphthalein ethyl ester

Abstract

It was found that sparteine could be extracted into 1,2-dichloroethane as a blue ion pair with tetrabromophenolphthalein ethyl ester (TBPE) and showed maximum absorption at 610 nm with a molar absorptivity of 9.56 × 10⁴ l mol^–1 cm^–1. Other secondary and tertiary amines were also extracted into 1,2-dichloroethane as the red associates with TBPE and showed maximum absorption at 545–585 nm. These associates showed reversible thermo-chromism with temperature change. The absorption due to amines except sparteine disappeared when the temperature of the solution was increased to about 60 °C. On the other hand, sparteine showed no thermochromism in 1,2-dichloroethane, although sparteine can be considered to be a tertiary amine. Accordingly, by using the principle of thermochromism, sparteine in the presence of other amines can be selectively determined in pharmaceutical products by spectrophotometry.