Composition and distribution of acidic compounds in Duba extracts: Revealed by negative electrospray ionization-Fourier transform ion cyclotron resonance-mass spectrometry

A modified version of base extraction was adopted to separate the acidic compounds, primarily naphthenic acids, in Duba crude oil. Extracts and residua were collected and subsequently characterized by negative electrospray Fourier transform ion cyclotron resonance mass spectrometry ( Neg ESI FT ICR MS). The results indicated that Neg ESI FT ICR MS was a powerful tool for the identification of acidic compounds in crude oil. The broadband mass spectra showed that acidic compounds distributed in all the fractions of extraction, and obviously differed in composition and relative abundance. The washing process could only extract the acidic portion with a molecular lower than 500 Da. Increasing in solvent volume and in polarity of reverse-extracting solvent tended to exclude more neutral nitrogen compounds. Meanwhile; this procedure had little influence on the composition and distribution of acidic compounds with a relatively low molecular weight.