Study On Separation Of Pyrrole From Tobacco By Molecularly Imprinted Technology

This paper was aimed at the separation and determination of pyrrole from the nitrogen-heterocyclic compounds by molecular imprinting technique(MIT) and providing with the experiment basis of the research of the nitrogen-heterocyclic compounds in tobacco. The molecularly-imprinted polymer (MIP) of pyrrole was synthesized by a precipitation polymerization method using different functional monomers and ethylene glycol dimethacrylate (EGDMA) as cross-linker agent in different porogens. The surface morphology and specific surface area of the MIP were characterized by different methods. Then the adsorption behavior of the MIP was investigated in detail. In this paper, the pyrrole in tobacco was extracted via simultaneous distillation and solvent extraction method. The optimum extraction technological conditions was determined with response surface methodology(RSM). The molecularly imprinted polymer solid-phase extraction(MISPE) column was prepared using MIP as sorbents, then the conditions of loading, washing and eluting were optimized. The process after optimization was used to separate the pyrrole in crude extracts from tobacco. The main results were as follows:1. The two composites which made from acrylamide and pyrrole, methacrylic acid and pyrrole were scanned by UV-Visible spectrophotometry, and the UV-Visible spectrograms indicated the acrylamide was better than methacrylic acid when used as functional monomer. Through the screening of the suitable dosage of acrylamide, the optimal molar ratio of pyrrole and AM was 1:4. Four molecularly imprinted polymers were prepared with acetonitrile, methanol, tetrahydrofuran and N,N-dimethyl formamide as porogens, respectively. Acetonitrile was selected as porogen after comparing the characters of different molecularly imprinted polymers.2. The structures of the MIP and non-imprinted polymer(NIP) were characterized by FT-IR, the results showed that the synthesis of the polymer proved to be successful, and the MIP and NIP wre both had the same chemical composition, but they showed big difference in space structure. The prepared MIP and NIP were microsphere which distributed within a narrow particle size, the average diameters of MIP and NIP were 2 μm and 3μm, respectively. The results of nitrogen adsorption showed the specific surface area of MIP was higher than NIP, but the pore diameter of MIP was smaller, this MIP’s internal structure provided favorable conditions for its specific adsorption. The thermogravimetry analysis indicated the thermostability of MIP was considerably high, and was higher than NIP.3. The binding property experiments indicated the imprinted polymer could adsorb the pyrrole molecule selectively. The adsorption quantity of MIP and NIP increased with time, and the saturated bindings were observed after 80 min and 60 min, respectively. The MIP took a long time to reach equilibrium, this indicated that the existence of specific holes in MIP made it’s adsorption process more time-consuming. The maximum adsorption quantities of pyrrole on the MIP and NIP were 404 and 265 μmol·g-1, through the Langmuir equation and Scatchard analysis. It is manifested that the affinity between MIP and pyrrole was much higher. The selective adsorption experiments demonstrated the MIP has higher selective adsorption with pyrrole molecule when compared whith pyridine.4. To obtain the optimal process conditions for the extraction of pyrrole from tobacco, the effects of the dosage of salt, sample mass and extracting time on pyrrole yield were investigated by single factor method and response surface method. The optimal extraction conditions were as follows:the dosage of salt was 108 g, sample mass was 20.5 g, extracting time was 2.3 h, the predicted yield of pyrrole was 2.76 μg/g under this condition. The average verification test showed that the actual yield of pyrrole was 2.68 μg/g, which was very close to the predicted yield, and this provided a certain dependability of the test results.5. The MISPE column was prepared using MIP as sorbents. The optimized conditions of solid-phase extract were loading pyrrole dichloromethane solution at a rate of 1 mL/min, washing with 20% acetonitrile water solution and eluting with 10% acetic acid methanol solution. Under this conditions, the recovery of pyrrole was 86.78%.6. The optimal molecularly imprinted solid phase extract condition was adopted to extract pyrrole in tobacco. The tobacco extract before and after the separation were analyzed by GC/MS. The results demonstrated that the content of pyrrole in tobacco extract increased from 8.30% to 45.60%. The test results indicated the MISPE column which prepared using MIP as sorbents could separate pyrrole from the nitrogen-heterocyclic compounds in tobacco.