Crude acids or petroleum acids are considered to be one of the prime contributors to corrosion, emulsion, and fouling issues across upstream, downstream, and chemical operations. Thus, the composition of crude acids has been extensively studied in the last several decades. To achieve molecular level characterization, mass spectrometry is typically applied. However, one of the challenges in mass spectrometry characterization is that the dynamic range of the technique can severely limit the compositions observed. Here, we employ multiple separations before analyzing crude oil acid fractions to overcome this limitation. First, a whole crude (WC) oil was distilled into boiling point fractions including vacuum gas oil (VGO) and vacuum residue (VR). Acids were then collectively isolated from the VGO and VR fractions as well as the starting WC using a solid phase extraction (SPE) method. Isolated acids were also further separated by molecular weight (MW) using a similar SPE technique. The acid fractions were then characterized by negative -ion (-) electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). This combined analytical approach produced a comprehensive acid composition of the crude oil and a more accurate distribution of the acids as a function of boiling point. A comparison of the WC acid fractions to the VGO and VR acid fractions reveals that direct analysis of the WC fractions does not cover the full composition as exhibited through the combined analysis of the VGO and VR fractions. Thus, further fractionation of the crude oil, such as through distillation, aids in overcoming dynamic range limitations associated with FT-ICR MS.