A novel spectrophotometric method for the determination of aminophylline in pharmaceutical samples in the presence of methanol

A rapid, simple and sensitive method for the determination of aminophylline (Ami) using sodium 1, 2-naphthoquine-4-sulfonate (NQS) and methanol is established in this paper. It is based on the fact that a russety product can be formed by the reaction between aminophylline (Ami) and sodium 1, 2-naphthoquine-4-sulfonate (NQS) in pH 13.00 buffer solution. When methanol is added to the solution, the sensitivity of the color development reaction between Ami and NQS is improved, and the color of the system of NQS–Ami becomes a salmon pink. Beer's law is obeyed in a range of 4.97–69.5 μg ml−1 of Ami at the maximum absorption of 453 nm (ɛ = 4.87 × 103 l mol−1 cm−1). The linear regression equation of the calibration curve is A = 0.14458 + 0.00832C (μg ml−1), with a linear regression correlation coefficient of 0.9944. The detection limit is 0.7 μg ml−1 (3σ/k), R.S.D. is 1.1% and the recovery rate is in range of 92.5–105%. Furthermore, this method has been successfully applied to the determination of Ami in pharmaceutical samples.