Simple and rapid paper-based colorimetric spot test for promethazine screening in recreational drug beverages and pharmaceuticals

Abstract

This study introduces a paper-based colorimetric spot test for the rapid and cost-effective detection of promethazine, featuring enhanced stability and user-friendliness. The developed device employs a potassium persulfate reagent encapsulated in a xerogel matrix, facilitating a simple chemical oxidation reaction that produces a pink color upon promethazine detection. Color quantification is efficiently achieved using a digital camera, with image analysis performed through ImageJ software to convert color image into a blue intensity scale. Under optimized conditions, the method demonstrates a linear calibration curve within the range of 100–600 mg/L and a detection limit of 20 mg/L. The paper-based colorimetric spot test exhibited good intra-day and inter-day accuracy of the recoveries of 98–102 % and 99–101 %, respectively. Good precision of measurement was also achieved (5.6 % RSD). The xerogel matrix ensures the long-term storage stability of the reagent for three months when stored at both 25 °C and 4 °C, making the device suitable for field applications. When applied to detection of promethazine in recreational drug beverage samples and pharmaceutical formulations, the performance of the proposed method showed no significant statistical differences compared to gas chromatography–flame ionization detection (GC–FID). This low-cost, portable, and disposable tool is suited for onsite screening of promethazine, representing a significant advancement in rapid drug detection methodologies.