RESUMO
Ion pair extraction coupled with digital image colorimetry has been developed as a promising platform for pharmaceutical analysis. The applicability of the approach was demonstrated through the assay of chlorpromazine hydrochloride tablets. In this method, the colorless, positively charged drug reacted with an anionic methyl orange dye in 1.5 mL microcentrifuge tubes, forming a yellow ion pair complex, which was extracted one time using a green solvent, i.e., ethyl acetate. Without the isolation or transfer of the liquid phase for dilution or measurement in a cuvette, a set of multiple tubes consisting of standards and samples were placed in a radial alignment above the white-light-illuminating screen of an iPad in a closed dark box and an image was taken in a single shot from the top of the box using an iPhone camera. The intensities of the yellow color of the extracts were transformed into red-green-blue (RGB) pixels using a mobile application, and the B values divided by the total of R + B + G were used as the analytical signals, which were plotted against the drug concentration to construct a standard curve. The proposed method showed good linearity (R2 = 0.9998) over the concentration range of 2.5-50 µg mL-1 with a limit of quantitation of 2.30 µg mL-1. The proposed method was accurate, precise, and free from interferences by excipients used in tablets, thus yielding assay results with no significant difference from those analyzed using the United States Pharmacopeia 42 reference method. Moreover, the proposed method is exceptional because it can be rapidly and easily used, requires relatively inexpensive instrumentation, can be safely utilized by analysts, and is environmentally friendly. Therefore, the proposed assay platform has considerable potential for application to routine quality control and analysis of drug formulations in the pharmaceutical industry.
