This research outlines a fast and efficient technique for separating the pyrrolic, phenolic-ketonic, and carboxylic acid fractions from oils in a small-scale setting. This approach enables the separation and analysis of neutral nitrogen fractions that contain indoles, carbazoles, and benzocarbazoles, as well as ketonic-phenolic fractions that contain phenols and ketones. The study showcases the potential for accurately measuring petroleum composition. The reliability of the fractions’ concentration results is determined by the mass of the separated fraction, with completely reliable results achievable for masses exceeding 1.4 mg. The fraction’s mass can also be used to evaluate the relative expanded uncertainty of a single separation procedure. As the mass and concentration of the fraction increase, the relative expanded uncertainty of the concentration decreases, and this can be modelled using a power function.