Spectrophotometric Determination of Thiols in Pure Substances and Pharmaceutical Preparations

A spectrophotometric method for determination of mesna (MA), 6-mercaptopurine (MP), 6-thioguanine (TG), and 6-propyl-2-thiouracil (PTU) has been developed. The method was based on the reaction of thiouracils with N,N-dimethyl-p-phenylenediamine (DMPD) in acidic solution in the presence of the Fe3+ ion, an oxidising agent. Absorbance of the obtained coloured products was measured at the corresponding optimum wavelengths: 490 nm for MA (ε = 1.9 × 103 L mol–1 cm–1), 455 nm for MP (ε = 1.9 × 103 L mol–1 cm–1), 460 nm for TG (ε = 1.6 × 103 L mol–1 cm–1), and 465 nm for PTU (ε = 2.1 × 103 L mol–1 cm–1). Beer’s law was obeyed in the following concentration ranges: 8.2 × 10–3–9.0 × 10–2 g L–1 for MA, 6.0 × 10–3–3.8 × 10–2 g L–1 for MP, 4.2 × 10–3–4.2 × 10–2 g L–1 for TG and 4.2 × 10–3– –3.9 × 10–2 g L–1 for PTU. The method has been applied for determination of thiols in pharmaceuticals.