DESENVOLVIMENTO DE MÉTODO COLORIMÉTRICO PARA DETERMINAÇÃO DO AMINOÁCIDO 5-HIDROXITRIPTOFANO EM FÁRMACOS

Abstract

L-5-hydroxytryptophan (5-HTP) is an aromatic amino acid produced in the human body from L-tryptophan, derived from dietary proteins. However, supplementation with L tryptophan does not significantly increase 5-HTP levels, which is mainly obtained from the seeds of Griffonia simplicifolia Baill. and widely used as a dietary supplement. Due to its therapeutic application in the treatment of conditions such as depression, fibromyalgia, insomnia, obesity, and chronic headaches, the accurate determination of 5 HTP is essential to ensure the quality of pharmaceutical and dietary supplement products. In this work, a simple and low-cost colorimetric method was developed for the determination of 5-HTP, based on the reaction with the Folin–Ciocalteu reagent and the analysis of digital images acquired using a smartphone. The reactions were carried out in microwells of a miniaturized device fabricated by 3D printing, with image acquisition performed under controlled lighting, positioning, and distance conditions. The color intensity of the reaction product was evaluated using the RGB color system with the aid of the Colorimeter application. Optimization studies involving reaction volume, reaction time and reagent concentration were conducted, establishing the following optimal conditions: total volume of 40 µL (24 µL of 5-HTP solution, 8 µL of 0.10 mol·L⁻¹ Folin Ciocalteu reagent, and 8 µL of 7.5% Na₂CO₃ solution) and a reaction time of 20 minutes. An analytical curve was constructed over the concentration range from 1.5 to 12.0 mg·L⁻¹, with a determination coefficient of 0.9948, indicating satisfactory linearity and RSD values below 13 %. The limits of detection (LOD) and quantification (LOQ) achieved were 0.346 mg·L⁻¹ and 1.155 mg·L⁻¹, respectively. In the interference study, common inorganic ions did not significantly affect the colorimetric signal of 5-HTP, whereas reducing species, such as ascorbic acid and catecholamines, promoted pronounced interference. The proposed colorimetric method was applied to the quantification of 5 HTP in pharmaceutical samples. Method accuracy was verified by comparison with UV Vis spectrophotometry, showing good agreement between the results, with relative errors below 10%. All analyzed pharmaceutical samples complied with the specifications established by the Brazilian Pharmacopoeia for active ingredient content. The results indicate that the proposed method is precise, reliable, and presents potential for application in routine analyses and quality control of commercial 5-HTP supplements.