A Polymer-Based Indicator for Detecting Dexamethasone in Herbal Medicine Using Polymethylmethacrylate (PMMA)

Dexamethasone is a chemical drug that is usually added to herbal medicine because of its effects on pain relief, arthritis, anti-inflammation, etc. Chemical drugs should not be used in herbal medicine because uncontrolled consumption causes some side effects. A polymer-based indicator was developed to detect dexamethasone in herbal medicine samples in a fast and simple way compared to instrumental analysis. The indicator strips were made by mixing polymethylmethacrylate (PMMA) polymer with sulfuric acid (H₂SO₄) as a reagent. When reacting with dexamethasone, H₂SO₄ can cause the color to change into a specific light pink-purple color. Indicator strips were prepared with a composition of 5% PMMA in ethyl acetate:H₂SO₄ (9:1) by using the reagent blending method. The indicator strips showed a pink-purple color when they were applied to a positive herb containing dexamethasone. The indicator strips could selectively detect dexamethasone rather than other active substances that are often found in herbal medicine. These indicator strips could also detect dexamethasone with the smallest detection limit of 13.13 ppm, and they had a stability of up to 36 days. Detection was carried out in real samples to show the performance of the indicator strips. The result showed that of nine samples, five were confirmed to contain dexamethasone. These results showed a good agreement with the results of thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC). According to the result, these indicator strips provide a simple and applicable method for on-site analysis to detect dexamethasone in samples.