Green first-order derivative synchronous spectrofluorometric analysis of valsartan and metolazone in pharmaceutical and biological matrices

In this work, a green facile, sensitive, and rapid spectrofluorometric method was developed to assay two antihypertensive drugs, namely, valsartan (VST) and metolazone (MTZ), in pharmaceutical and biological matrices. Both drugs exhibited intrinsic fluorescence which was significantly influenced by environmental factors such as solvent system and pH.  However, simultaneous analysis of VST and MTZ by conventional spectrofluorimetry cannot be performed easily due to the severe overlap of their fluorescence spectra. Therefore, combination of synchronous and derivative spectrofluorimetry was investigated to solve such dilemma. The developed method relied on measuring the first-order derivative of synchronous flourescence intensity of the studied analytes in 0.1M acetic acid at Δλ=160nm. The peak amplitudes of the recorded first-order derivative synchronous flourescence spectra of VST and MTZ were measured at 262.8nm (zero-crossing point of MTZ) and 236.0nm (zero-crossing point of VST) to simultaneously assay VST and MTZ, respectively. The method was optimised carefully to obtain maximum sensitivity and selectivity by investigation of different solvent systems, different pH, and different micelles. The optimum selectivity and sensitivity were obtained, using 0.1M acetic acid as a solvent. The proposed method had a linear concentration range (10.0–100.0 ngmL⁻1) and a detection limit (<2.0 ng mL⁻1) for each drug. Statistical analysis of the data manifested no significant differences between the developed spectrofluorimetric method and the comparison methods. The method validity ensures its appropriateness for quality control work. The developed spectrofluorimetric method was applied to assess the studied analytes in pharmaceutical preparations and biological fluids with high %recovery and low RSD values. The greenness of the method was implemented by three approaches involving the recently developed metric (AGREE) which ensured the eco-freindship and safety of the method.