Identification of 5-hydroxyindoleacetic Acid in Urine with a Paper-based Colorimetric Test

A BSTRACT Objective: Detecting 5-hydroxyindoleacetic acid (5-HIAA), a vital metabolite in urine, is crucial for diagnosing and monitoring carcinoid tumors. Traditional methods such as spectrophotometric analysis and high-performance liquid chromatography provide high selectivity and sensitivity but are costly and unsuitable for on-site testing. Materials and Methods: Recently, paper-based analytical devices have emerged as innovative solutions for detecting various substances, including chemicals, environmental pollutants, and microorganisms. This study investigated the use of Whatman filter papers No. 1, No. 2, and No. 4, along with Whatman chromatography paper, to develop a paper-based assay for 5-HIAA using Ehrlich’s reagent. Results: Optimization showed that an immersion time of 180 min and a drying time of 30 min at room temperature were most effective. Conclusion: Among the tested filter papers, Whatman CF6 paper demonstrated the best performance for 5-HIAA detection.