Development and validation of a new Fourier transform infrared spectrometric method for the quantification of urea in creams and ointments

A new Fourier transform infrared (FTIR) spectrometric method for the quantification of urea in creams and ointments was developed and validated. The sample was solubilized in a mixture of chloroform/acetonitrile (1/1 v/v) which allows to solubilize the vaseline or other fats as well as urea and water. The solution was examined in a transmission cell with a pathlength of 500 μm provided with NaCI windows. The urea spectrum was obtained by subtraction of the reference solvent mixture spectrum and the reference water spectrum from the sample spectrum. The absorbance of the peak at ±1688 cm-1 was compared to those of calibration standards to quantify urea. The detection limit and the quantification limit (three times and 10 times the noise, respectively) were estimated as 0.4 and 1.3 μg ml-1, respectively. Validation of the method was realized and application of this method to stability tests was done.