Spectrophotometric determination of penicillins in pure and pharmaceutical formulations using Folin-Ciocalteu reagent.

A new combination of time, temperature, and alkali is described for the spectrophotometric determination of amoxicillin and ampicillin using Folin-Ciocalteu reagent. The method is based on the development of blue-coloured product due to the reduction of tungstate and/or molybdate in Folin-Ciocalteu reagent by amoxicillin and ampicillin in alkaline medium. The chromogenic reaction has λ(max) at 720 and 740 nm with molar absorptivity 1.6295 × 10⁴ and 0.1085 × 10⁴ l mol⁻¹ cm⁻¹ in the Beer's Law range 2-10 µg mL⁻¹ and 10-70 µg mL⁻¹ for amoxicillin and ampicillin, respectively. The method is reproducible, quick, inexpensive, and particularly helpful in determining the drug content in commercial dosage forms.