Compound Specific Carbon Isotopic Ratio Analysis Of Polycyclic Aromatic Hydrocarbons In Soil Samples

Polycyclic aromatic hydrocarbons (PAHs) pollution has become a global issue. Investigation on the characteristics of distribution, source, migration and transformation of PAHs can provide essential imformation for polution control. The current techniques, such as molecular marker approaches and mathematical modeling, assume limits on acurate discrimination for the sources of PAHs, but their combinative employment has been demonstrated effective. To identify sources of PAHs, development of new methods for source apportionment of PAHs is increasingly to be of concerned. The compound specific carbon isotope analysis (CSIA) of individual PAHs is one of the most popular method and getting more attention these years. However, low precision and poor accuracy for CSIA of individual PAHs have become barriers of their traceability.Contrary to the 16 EPA priority PAHs, a method for CSIA of individual PAHs in soil samples was researched including sample pretreatment method and detection technique. Effect of GC separation process on ?13C values of PAHs was disscussed. Results indicated that optimal analytical conditions was as follows:held for 5min in initial temperature at 60? in oven,, then, then rose from 60? to 320? at a rate of 4? min-1, held for 10 min at 320?. Helium was choosen as GC carrier gas at a constant flow rate of 2.0 ml min-1. The programmed temperature vaporizer (PTV) injector operation parameters was also be optimized. Injector mode, splitless time, the injection volume, the temperature of the injector, evaparation temperature,transfor temperature,solvent evaporation time,sample transfor time and the pressure of the injector were selected as PTV solvent splitless mode as follows:1.5min,5?L,55?,55?,320?,2.5min, 1.5min and 40psi?60 psi?70 psi respectively. The GC-C interface operation parameters was temperature of oxidation furnace and the reduction furnace was 950? and 640?. Besides we use capillary pre-column to improve the peak shape of polycyclic aromatic hydrocarbons(injection volume 5?L).Benzo a pyrene, Indeno 123-cd pyrene, dibenzo a, h anthracene and benzo g, h, i perylene peak intensity increased by 200-300mv, benzo a pyrene and benzo g, h, i perylene peak width were reduced by 22s and 14s. Under the optimized instrument conditions, the determination precision of ?13C values on 16 kinds of PAHs (three pairs of isomers were calculated by a peak respectively) between 0.1‰ and 0.45 ‰.813C values of three solid phase PAHs standard and two alternative internal standard measured by EA-IRMS and GC-IRMS. ??13C of these material measured by two different methods between 0.01‰-0.63‰.It is within the instrument error range,so we conclude that GC-C-IRMS instrument analysis method does not result in carbon isotopic fractionation of PAHs monomer.In addition,we reasearched the purification effect of amino solid phase extraction(SPE) column and different size of silica gel solid phase extraction column.Results indicated 500mg size of amino SPE column and 500mg size of silica gel SPE column in the experimental design of the sample volume (impurities:PAHs=30000ng:3000ng) under both pass through. While silica gel SPE column was more effective than amino SPE column in separation of impurities. So 1000 mg of silica gel SPE columns and elution solution were choosen and studied. We use silica gel SPE column clean with n-pentane and n-pentane:dichloromethane= 70:30 (V/V) continuous leaching, most impurities and UCM interference can be removed, chromatograms baseline became low and flat,5ml pentane:dichloromethane mixed solvent leaching, the range of PAHs recoveries was 74%-128%, relative standard deviation was 3%-18%(n= 6). The carbon isotope composition of PAHs can be measured with a standard deviation (S.D.) from 0.1%o to 0.8%o (n=6). Samples with high impurity content needs secondary purification and the recovery of volatile naphthalene reduced to 65%.The relative standard deviation of secondary purification procedure was 8%-20% (n= 6).The carbon isotope composition of PAHs can be measured with a standard deviation (S.D.) from 0.1‰ to 0.72 ‰ (n=6). Whether firstly or secondary purification procedure, the difference of ? 13C values of each compound between proceed and unproceed standard was ranged from 0.01‰ to 0.99%o. No significant isotope fractionation occurred during the SPE column purification process. Finally, the established pretreatment and analysis method were applied successfully to soil samples.