A Simple Strategy for Methylene Blue Determination in Human and Veterinary Dosage Forms by Digital Imaging

Abstract

A colorimetric method based on digital image processing and an image capture device as a detector has been developed for determining methylene blue (MB) in human and veterinary dosage forms. Operational variables, such as capture devices, angle and modes of capture as well as measuring vessel geometry, were evaluated in order to establish the most suitable conditions to obtain accurate measurements. Three different capture devices including a webcam, a compact digital camera and a smartphone camera were compared. Digital images were analyzed using the open source program ImageJ. Suitable results were achieved when using a 20.7 MP back camera of a smartphone and white-LED lighting conditions. Grayscale values were finally employed as response to determine MB concentration. Satisfactory linearity was achieved in the concentration range from 3.5 × 10–7 to 4.7 × 10–6 M, with the determination coefficient R2 > 0.97 and the limit of detection of 1.7 × 10–7 M. The proposed approach was successfully applied to the detection of MB in two commercially available dosage forms for human and veterinary treatment.