Study on the Influence of Pre-treatment Conditions of Poly-nuclear Aromatic Hydrocarbons Samples of Geochemical Exploration for Oil and Gas

The content of poly-nuclear Aromatic Hydrocarbons is a very important index to trace abnormalities in regional oil and gas for geochemical exploration samples. The extraction efficiency of the target compounds is influenced by many pre-treatment conditions such as extraction solvents, grain size, shaking time, standing time and extraction temperature. The above-mentioned conditions were studied systematically in this research with oscillation extraction for oil and gas geochemical exploration samples. Based on research results, the solvent plays an important role in preparation. The extraction efficiency of solvents in turn from high to low are dichloromethane, n-hexane, ethyl acetate and petroleum ether. Considering the background effect of different solvents to measured results, the n-hexane was selected to study the experimental conditions. The fluorescence intensity was reduced when grain size was below 0.090 mm. Satisfactory data can be obtained when sample grain size is between 0.125-0.090 mm. The fluorescence intensity was increased simultaneously with increasing oscillation time and hold time. When the hold time extended to 9 h, the extraction efficiency was improved insignificantly. The oscillation time has a minor effect on extraction efficiency while more than 20 min oscillation time does not improve the extraction efficiency. The extraction temperature plays an important role for extraction efficiency. Under the same conditions, the fluorescence intensity was increased when the temperature was raised. The temperature is the most important factor for the repeatability test. The experimental conditions were optimized with grain size of 0.125-0.090 mm, solvent of dichloromethane, extraction temperature of 25℃, 20 min shaking time, and 12 h hold time.