Methodology for Methylene Blue Analysis from Polymeric Systems Used in Photodynamic Therapy: Comparison of Two Methods for Quantification

Methylene blue (MB) is used in association with photodynamic therapy for the treatment of many cutaneous diseases. The development of analytical methodologies for quantification of chemical substances is extremely useful to content determination of drug on pharmaceutical products. Two proposed methodologies (spectrophotometric and high-pressure liquid chromatography) were evaluated for MB determination. Both methods showed linear dependence between absorbance or pike area and MB concentrations, with a coefficient of determination of 0.9968 and 0.9965 for the spectrophotometric and chromatographic methods, respectively. Variance and residue's analysis showed that the methods had significant linear regression with no lack of fit. Both methods were accurate, precise, exact and robust. The spectrophotometric method was more sensitive than chromatographic, by analysis of limit of detection and limit of quantification. Spectrophotometric method was adequate to evaluate the MB concentration from polymeric systems of poloxamer and Carbopol, enabling their quantification on 30-days preliminary stability test at 25 degrees C.