Diazocoupling reaction for the spectrophotometric determination of physiologically active catecholamines in bulk and pharmaceutical preparations

A simple and sensitive spectrophotometric method for the determination of four catecholamines viz., adrenaline bitartarate (ABT), methyldopa (MDP), dopamine hydrochloride (DPH), and levodopa (LDP), in both pure form and in pharmaceutical formulations is described. The method is based on the reaction of diazotized sulphanillic acid (DSA) with catecholamines in a basic medium to yield orange-red colored products having absorption maxima at 507 nm for MDP and at 475 nm for others analytes. The colored species obeyed Beer’s law in the range of 1–27, 0.5–17, 0.6–15, and 1.5–19.2 μg/mL for ABT, MDP, DPH, and LDP, respectively. The molar absorptivity values as obtained from Beer’s law data were found to be 0.812 × 10⁴, 0.947 × 10⁴, 0.927 × 10⁴, and 0.709 × 10⁴ L/(mol cm), while Sandell’s sensitivity values were observed to be 412.03, 25.15, 20.44, and 27.81 ng/cm² for ABT, MDP, DPH, and LDP, respectively. Common excipients did not interfere with the proposed method. The results of the proposed methods compare favorably with those of official methods. The proposed method offers a simplicity, reliability, rapidity, and accuracy compared to the existing methods. The text was submitted by the author in English.