Sustainable multi-analyte HPTLC estimation of meloxicam, diclofenac and diacerein along with its major degradation product and official impurity; rhein: Comprehensive greenness and whiteness evaluation

A sustainable HPTLC method has been developed for the simultaneous determination of Meloxicam (MLX), Diclofenac (DCF) with Diacerein (DCN), and its pharmacopoeial impurity and main degradation product, Rhein (RIN). Reviewing the literature revealed that no HPTLC method has been reported for the simultaneous determination of the three cited drugs along with RIN. Merck TLC plates precoated with 60F 254 silica gel on aluminium sheet were used as stationary phase and were developed with a green mobile phase composed of ethyl acetate: ethanol: water (9.5: 1: 0.5 v/v/v respectively). Densitometric scanning was performed at 259 nm for DCN and RIN, while MLX and DCF were detected at 360 nm and 281 nm, respectively. The proposed method was validated according to the ICH guidelines regarding linearity, range, accuracy, precision, specificity, and robustness. Additionally, the environmental impact of the developed method was assessed using the analytical eco-scale (AES), the green analytical procedure index (GAPI) and the Analytical GREEnness calculator (AGREE). Moreover, the method's sustainability was evaluated and compared with previously published methods using the novel RGB 12 model in terms of the 12 white analytical chemistry (WAC) perspectives. Finally, successful application of the proposed method was carried out for the estimation of the cited compounds in their combined formulations as well as for the detection and quantification of DCN impurity; RIN, at concentrations below its pharmacopoeial limit. The present study represents the first sustainable and economic HPTLC separation and determination of the four cited compounds simultaneously as well as a sensitive method for testing the purity of DCN in bulk form and combined formulations.