In terms of sample pre-treatment, there is a tendency of using methods to prevent its intensive manipulation [6]. The direct analysis of the diluted sample with organic solvent, due to its convenience and speed, has been widely used. However, organic standards, apart from being relatively expensive and difficult to prepare, can lead to erroneous results. It may be because of the alteration in the concentration caused by evaporation of solvent and metal deposition on the walls of the deposit containers [8,20,21]. Aucélio et al. [6] also pointed out problems of repetition and false results due to the presence of insoluble inorganic species in used lubricant oil.