The lack of samples with similar composition in water content was a serious problem in evaluating the accuracy of the method. In order to obtain some significant values to account for accuracy, some determinations of elements under study (V and Ni) were made using a representative sample of Cerro Negro bitumen (the natural bitumen currently used to prepare Orimulsion), using the procedure described here and these values were compared with those obtained using a wavelengthdispersive X-ray fluorescence (WDXRF) method.