This paper describes the development and application of a simple,
portable, and environmentally friendly method for the rapid determination of furosemide in urine. The proposed method is based on the complexation reaction of furosemide, dissolved in ethanol, with
FeCl3 in the presence of dodecyltrimethylammonium bromide
(DTAB) in aqueous solution, yielding a colored compound on the surface of a filter paper (λmax=477 nm). Experimental design methodologies were used to optimize the measurement conditions.