Polycyclic aromatic hydrocarbons (PAHs), a kind of persistent organic pollutants in soil, are of great concern due to their carcinogenic, mutagenic and teratogenic characteristics. PAHs are mainly derived from incomplete combustion processes and pyrolysis of organic materials. The occurrence, source, transport and fate of PAHs in various environments have been reported extensively, while the determination method of PAHs varied in the past reports. Thus the accurate analysis of PAHs is a vital step for further research. The PAHs are usually extracted and purified by organic solvent prior to determination. In order to improve determination accuracy and recovery rate, the pretreatment conditions for the determination of 16 PAHs in paddy soils are of great significance.
On the basis of former work, in order to get the highest extraction efficiency and recovery rate, we compared two different extract solvent mixtures, four different clean-up columns and three different elution solutions, and also compared the elution volume and temperature of nitrogen blowing to optimize the determination method for trace PAHs in paddy soils under the laboratory condition. Soil samples were taken from paddy field in Wenling City of Zhejiang Province, and the polluted soil samples were made by adding PAHs standard solution. The analysis of target compounds was performed by gas chromatography-mass spectrometry (GC-MS).
The results showed that the soil samples were extracted ultrasonically three times with V(n-hexane):V(acetone)=1:1 mixture, followed by clean-up with C18 solid phase extraction (SPE) column and 8 mL of V(n-hexane):V(dichloromethane)=7:3 mixture elution solution, and the nitrogen blowing temperature was 20 ℃, which was the optimal pretreatment procedure. The correlation coefficients (R²) for the tested 16 PAHs were 0.999 0-0.999 9 within the range of 10-1 000 μg/L. The method detection limits were in the range of 0.022-0.470 μg/kg. The average recovery rates of the spiked samples ranged from 70.2%-110.8% with relative standard deviation (n=5) of 1.8%-9.8%.
In sum, the above results suggest that the established method in this study is accurate, sensitive and reliable; meanwhile, it can also reduce the cost of organic reagent. This method is suitable for the analysis of trace PAHs in paddy soils.