Sensitive spectrophotometric methods for the determination of pindolol

Abstract

Two simple, sensitive and reproducible visible spectrophotometric methods for the determination of Pindolol in amounts as low as 1 μg are described. The first method is based on the oxidation of Pindolol by sodium nitrite under acidic conditions and the coupling of the oxidised intermediate withN-1-(naphthyl)ethylenediamine dihydrochloride (NED) to the colored product. The spectrum of the colored solution is strongly dependent on the length of the incubation period at room temperature during oxidation (3 min, λ_max 620 nm; 10 min or above λ_max 540 nm). Other couplers [diphenylamine (DPA) or 1-naphthylamine (α-NA)] or indole derivatives (indole, tryptophan or isatin) when used instead of NED or Pindolol, respectively, also react to give a colored product with same maximum in each case irrespective of the length of the incubation period during oxidation. The second method is based on the coupling reaction involving Pindolol and 1,2-naphthaquinone-4-sulphonic acid sodium salt to form a coloured product (λ_max 660 nm). Both the methods have been employed to determine Pindolol content in bulk forms and pharmaceutical preparations.