A micro-solid phase extraction in glass pipette packed with amino-functionalized silica for rapid analysis of petroleum acids in crude oils

In this work, a micro-solid phase extraction (micro-SPE) method was developed for the analysis of petroleum acids in crude oils. Plastic vessels were found to be unsuitable as the micro-SPE vessel, because of the plasticizer interferences and the serious adhesion of oil samples on vessel surfaces. To reduce or eliminate these influences, a glass pipette was selected as the micro-SPE vessel. With the glass pipette micro-SPE format, amino-functionalized silica was chosen as the sorbent for extraction of petroleum acids based on mix-mode hydrogen bonding/ion-exchange interactions. The conditions of the micro-SPE were carefully optimized. Under the optimized conditions, no evaporation was needed, which can save time and reduce losses of analytes. By coupling with gas chromatography-mass spectrometry (GC-MS), the proposed micro-SPE method for analysis of petroleum acids was proved to be easily operated, fast (the micro-SPE can be accomplished within 5 min), solvent-saving (3 mL of solvent), reproducible and sensitive (the limits of detection range from 2 ng g−1 to 6 ng g−1).