Solvent extraction–spectrophotometric determination of berberine and benzethonium in drugs with tetrabromophenolphthalein ethyl ester by batchwise and flow injection methods

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Abstract
A spectrophotometric method for the determination of berberine and benzethonium in drugs was studied using batchwise and flow injection techniques coupled with solvent extraction. Tetrabromophenolphthalein ethyl ester (TBPE·H) in 1,2-dichloroethane reacted with berberine and/or benzethonium to form a blue ion associate whose absorbance was determined at 610 nm. The extraction conditions were studied using a batchwise method. On the basis of the results obtained with the batchwise method, a three-line manifold was constructed. The sample was injected into a distilled water stream and the pH adjusted to 11 with a borate-phosphate buffer solution. Then the stream was mixed with the extracting TBPE·H reagent. The organic phase was separated with a polytetrafluoroethylene porous membrane (0.8 µm pore size). The sample throughputs were 45 h–1 for berberine and 30 h–1 for benzethonium. The calibration graphs were linear in the range 1 × 10–6–1 × 10–5 mol dm–3 for berberine and/or benzethonium and the relative standard deviation (n= 6) was 0.9% for 1 × 10–6 mol dm–3 berberine and 1.2% for 4 × 10–6 mol dm–3 benzethonium. The proposed method was used for the rapid and selective determination of berberine and benzethonium in pharmaceuticals.