Exploiting von Pechmann coumarin derivatization for spectrofluorimetric determination of formoterol in pharmaceutical...

A sensitive spectrofluorimetric technique exhibiting acceptable selectivity was established for the quantification of formoterol (FMT) via the von Pechmann condensation reaction, leading to the formation of intensely fluorescent coumarin derivatives. In this reaction, FMT interacts with ethyl acetoacetate in the presence of concentrated sulfuric acid, producing a fluorescent product. The emitted fluorescence was recorded at 445 nm following excitation at 361 nm. Experimental parameters influencing the reaction were carefully optimized to achieve maximum fluorescence response and method stability. The proposed method exhibited excellent linearity across the concentration range of 20-500 ng mL^-1, with a correlation coefficient (r) of 0.9998. The limits of detection (LOD) and quantification (LOQ) were found to be 4 ng mL^-1 and 12 ng mL^-1, respectively. Acceptable selectivity was demonstrated under the studied formulation conditions, as no significant interference was observed from commonly used pharmaceutical excipients, including lactose monohydrate, magnesium stearate, gelatin, titanium dioxide and placebo. A reaction pathway based on the reported von Pechmann condensation was proposed, and the method was validated in accordance with ICH guidelines. The applicability of the method was successfully demonstrated for the determination of FMT in pharmaceutical dosage forms, including content uniformity testing, showing satisfactory recovery results. Finally, the environmental impact of the method was assessed using various greenness evaluation tools, indicating a favorable greenness profile and practical applicability.