Determination of pentavalent antimony in antileishmaniotic drugs using an automated system for liquid-liquid extraction with on-line detection

An automated system for liquid–liquid extraction flow analysis (LLE-FA) for the determination of Sb(V) in antileishmanial drugs is presented. The method is based on extraction in a 5 mL glass extraction chamber of an ion pair formed between hexachloroantimoniate anion and rhodamine B cation into toluene. The detection system consists of a green light emitting diode (LED) and a photodiode. The system is controlled by a microcomputer using a program written in Visual Basic 3.0. The extraction process was optimized and the following experimental parameters were established: sample loop of 150 μL; reagent loop of 900 μL; stirring time of 100 s; phase separation time of 80 s; volumetric ratio of 1:1 (aqueous/organic). The method was in-house validated for the determination of Sb(V) in meglumine antimoniate. The following performance criteria were obtained: linearity of 0.9989, linear range of 7.0 × 10⁻⁵ to 7.2 × 10⁻⁴ mol Sb(V) L⁻¹, sensitivity of 1.61 × 10⁶ ± 2 arbitrary units L mol⁻¹ (P < 0.05), intra-assay precision of 3.5% (n = 5; 4.1 × 10⁻⁴ mol L⁻¹ Sb(V). Whereas the method is selective in the presence of Sb(III), As(III) and Pb(II) at concentrations up to one tenth of the concentration of Sb(V), As(V) interferes. The accuracy of the method was evaluated through comparison of results obtained from analyses of pharmaceutical formulations by the proposed LLE-FA method with those obtained by inductively coupled plasma optic emission spectrometry (ICP OES) and differential pulse polarography for total antimony and Sb(III), respectively. The proposed method presented an analytical frequency of eight analysis per hour and is suitable for Sb(V) determination in the quality control of drugs employed for the treatment of leishmaniasis.