Ultraviolet Spectrophotometry For The Determination Of Petroleum Contaminants In Soil

Pre-treatment techniques and analytical methods of petroleum contaminants in soil were summarized in this paper. Base on a detailed comparison of various analytical methods, the application of UV (ultraviolet spectrophotometry) method for the rapid analysis of petroleum contaminants in soil was investigated. First of all, the pre-treatment conditions were optimized. The influence of extractant and soil property (soil particle size and soil salinity) on the extraction efficiency were discussed.And the best pre-treatment program of UV method was selected. Then orthogonal experiment was designed to indicate the influence of temperature, extraction time and L/S (liquid/solid ratio) on extraction efficiency. The composition of petroleum contaminants in soil was determined by FT-IR and GC-MS methods. At last, soil samples from Gudao-Oilfield were determined by UV method, and the results of UV method were compared with those of gravimetric method.(1)The optimized operating conditions were determined. UE (ultrasonic extraction):the temperature was30℃, the L/S was8mL/g, the extraction time was15min, and then the sample was extracted twice; OE (oscillation extraction):the temperature was25℃, the L/S was8mL/g, the extraction time was8h, the oscillation rate was150r/min; SE (soxhlet extraction):the temperature was60℃, the L/S was36mL/g, the extraction time was16h. The extraction efficiency of dichloromethane was higher than that of hexane and petroleum ether. The extraction efficiency increased when the soil particle size increased, and the20～40mesh soil samples showed the highest recovery rate. The increase of the soil salinity could reduce the recovery rate. The main component of petroleum contaminants in soil can be extracted by the ultrasonic extraction. We recommend ultrasonic extraction (2times) and ultraviolet spectrophotometry as a rapid analysis of petroleum contaminants in soil because of its low dosage and short operating time.(2)Orthogonal experiments showed the influence of three main factors (temperature, L/S and extraction time) on the three pre-treatment techniques. The result indicated that the sequence of influence importance for UE was temperature> extraction time> L/S, for OE was extraction time> L/S> temperature, and for SE was temperature> L/S> extraction time.(3)The results of FT-IR and GC-MS showed that the petroleum contaminants could be extracted effectively by the above extraction methods and dichloromethane was the favorable extractant.(4)The petroleum contaminants content of the three soil samples from Gudao-Oilfield was1.72%,0.93%and1.98%, respectively. The determination results of UV method were lower than those of gravimetric method. But UV method could be used as a rapid analysis method in determination of petroleum contaminants in soil due to its good repeatability (The relative standard deviation ranged from1.97to3.86%). UV method was Suitable for the soil with low petroleum contaminants content.