Colorimetric paper-based test strip for detection of methylparaben in nonconforming health care products

Abstract

Methylparaben (MPB) is a preservative used in pharmaceutical and food products to inhibit microbial growth and is also recognized as an endocrine disrupting compound. This work presents a simple, low cost, and reliable colorimetric paper based analytical device (PAD) for point of use detection of MPB in nonconforming health care products. The test strip was prepared by immobilizing Fe³⁺ on a chitosan modified paper substrate. Detection relies on the coordination interaction between MPB and the immobilized Fe³⁺, which produces a violet color on the paper surface. A smartphone was used to capture images of the test strip, and the images were analyzed using an RGB color detector mobile application. The intensity of the magenta component was extracted and used for quantitative analysis. The smartphone-based method showed strong correlation between magenta intensity and MPB concentration over the range of 10 to 50 mg mL⁻¹ with a coefficient of determination (R²) of 0.989. The fabricated PAD demonstrated high accuracy, indicated by % recovery values ranging from 97.8 to 101.5, and precision with a relative standard deviation below 2 percent. The method was applied directly to determine MPB in health care products without any sample preparation. Statistical evaluation using t-test and F-test showed no significant difference between results obtained from the PAD and conventional colorimetric analysis. The developed approach enables rapid and practical on-site detection of nonconforming health care products.