Analysis And Elimination Of Trace Polycyclic Aromatic Hydrocarbons In Natural Tocopherols

The analytical method of the trace polycyclic aromatic hydrocarbons (PAHs) in natural tocopherols(TP) was studied in this paper. The protocol included two stages: enrichment of the PAHs, and analysis and determination of the PAHs. The elimination of trace PAHs in tocopherols was explored.In this paper, a high performance liquid chromatography (HPLC) method was established for the simultaneous determination of eighteen polycyclic aromatic hydrocarbons (PAHs). The chromatographic conditions, including separation column, composition of mobile phase, flow rate, and fluorescence detection wavelength were investigated. The optimal chromatographic conditions were: analytical column, XDB —C18 (4 .6 mm i.d. ×150 mm, 5 μm (Agilent));column temperature 35 ℃;mobile phase, acetonitrile-water, binary gradient condition were used: from 0 to 13 min, 40% water, 60% acetonitrile;from 14 to 22 min, 34% water, 66% acetonitrile;from 23 to 32 min, 20% water, 80% acetonitrile;from 35 to 47 min, 40% water, 60% acetonitrile. Seven wavelength shifts were adopted to achieve the most sensitivity. Calibration curves of 18 PAHs were linear from 2—200 ng/ml, the correlation coefficients were 0.9999.The PAHs in natural tocopherols were enriched by alumina column chromatography (15 mm i. d. ×300 mm). The choice of sorbent and the volume of elution solvent were investigated. Activity grade 4 aluminium oxide and hexane were used for the column chromatography, and the volume of elution solvent was 90 ml. The sensitivity, precision and accuracy were evaluated. The detection limits varied from 0.05 ng/(g TP) tol.8 ng/(g TP). RSD of the PAHs was less 10% and the recovery of the PAHs ranged from 23 % to 131.66%. Therefore, the method may be used in the analysis of the trace polycyclic aromatic hydrocarbons (PAHs) in natural tocopherols.Actual samples of 98.0% d-a-tocopherol, 54.0% mixed tocopherols, and 90.5% mixed tocopherols were analyzed using above method, and the results have good repeatability. The contents of PAHs in the three tocopherols were 404.07 ng/(gTP), 7723.70 ng/(g TP), 1659.16 ng/(g TP), respectively, and they all exceed the legal limits. So, the method was important in practice.The tocopherols were mixed with 5 times the volume of ethanol, to which 10% by weight of activated carbon(HC-2) was added, and were mixed for 45 min at 20℃. The method can produce a very substantial reduction for PAHs level in tocopherols (the light PAHs removal was above 48%;the heavy PAHs removal was above 98%;the total PAHs removal was above 88%). The content of heavy PAHs left in the tocopherols had already reached the limit (5 ng/(gTP)), but the content of light PAHs was still above the limit (20 ng/(gTP)).