Study On The Residual Content Of Carbamates In Liquor Based On Molecular Imprinting Technique

Methyl carbamate and ethyl carbamate belong to the carbamate pesticide which are carcinogens and lead to tumor. Liquor, as China’s traditional drink, was prepared from cereals. Toxic by-products including MC and EC were produced through the fermentation proces. The issue that whether pesticide residues are in liquor captures people’s great attention. Chromatography is generally used to dectect the content of MC and EC residues in liquor over the world. Sample pretreatment, the commom method of solid phase extraction, is the key factor of the detection because of the complexity of the wine matrix. Nevertheless, the interaction force is nonspecific between the adsorption agent of traditional SPE and the analyte that give rise to low extraction efficiency on analyte and impurity. According to the specific selection of molecularly imprinted polymers(MIPs), molecularl imprinted solid-phase extraction column was prepared to separate and concentrate the analytes in complex components selectively and remove the interference of matrix. So the sensitivity and accuracy of analysis could be improved.In this paper, methyl carbamate(MC) and ethyl carbamate(EC), as the template molecules, were used to synthesize the MC-MIPs and EC-MIPs correspondingly. Solid phase extraction columns were prepared with adsorbent MC-MIPs and EC-MIPs, which were used for pretreatment of liquor sample. The residues content of MC and EC in liquor were detected with Raman spectroscopy and GC-MS. The main contents are as follows:1. Study on synthesis and performance testing of MC-MIPs, EC-MIPsMC-MIPs and EC-MIPs were prepared by bulk polyerization with template molecule MC and EC. The optimum synthesis conditions are: the functional monomer(acrylamide(AM)), porogen(chloroform), cross-linking agent(ethylene glycol dimethyl acrylic ester(EDGMA)), n(MC/EC): n(AM): n(EDGMA) =1:4:20, constant temperature water bath reaction temperature(58℃). The adsorption properties of prepared MC-MIPs and EC-MIPs, which could reach to 25mg/g, were better than that of the blank polymer(NIPs), meanwhile the amout of target compounds(MC,EC) adsorbed by MC-MIPs and EC-MIPs was higher than the similar structure of carbamate pesticides(Isoprocarb, MTMC, Fenobucarb). The change of functional groups of polymers analyzed by infrared spectroscopy was used to judge whether the elution is completely. Compared with NIPs, many cellular type holes of the surface of MIPs were found through SEM. This indicated that specific cavities were formed that could recognize the target molecules. The amount of MC-MIPs and EC-MIPs did not change from 100℃ to 300℃ via testing of DSC-TG, which showed that the prepared polymers had good thermal stability.2. Preparation and optimization conditions of MC-MISPE and EC-MISPEIn this study, MC-MIPs and EC-MIPs were respectively used as adsorption filler of solid phase extraction column, and then the solid phase extraction conditions were optimized. The optimum conditions are: chloroform as solvent, flow rate(2.0 m L/min-1), leached by chloroform, methanol / water / acetic acid(8:1:1, v/v/v), instrumented by nitrogen gas blowing. Under these conditions, of which recovery rate reached to 85%. Comparing with the C18 solid phase extraction column, purification ability and enrichment effect of molecularly imprinted solid-phase extraction column are better.3. Qualitatively determination of the content of MC and EC in liquor by molecularly imprinted solid-phase extraction combined Raman spectrometerLiquor samples were pretreated by MC-MISPE and EC-MISPE and measured through Raman spectrometer. The determination conditions as followed: room temperature is 24℃, excitation wavelength is 780 nm, Raman spectrum wavelength range scans is between 63 to 3415 cm-1, 10 times of objective lens, the grating is 400 gr/mm, resolution is 4.7 to 8.7cm-1, sample is irradiated with power 25 m W. Firstly, the Raman spectra of standard MC and EC were established, and then 10 kinds of liquor samples got detected. The results showed that there was one kind liquor sample with EC. This method is quick and easy, and the time of sample qualitatively detection is greatly shortened.4. Qualitatively and quantitatively determination of the content of MC and EC in liquor by molecularly imprinted solid-phase extraction combined GC-MSThe analytical method were established by MISPE combined with GC-MS, which was used to detect residues of MC and EC in liquor. With the best condition of solid phase extraction and detection of liquor samples, the detection limit of MC and EC were between the range of 2.66~6.53 μg?L-1. The added concentrations of MC and EC in liquor samples were between 1 mg/L to 5 mg/L and the average recovery rate was about 85.70%, the relative deviation was 3.61% and 2.52% respectively. Samples enriched and purified by MISPE column and C18 solid phase extraction column were compared, the sample recovery rate and purification of MISPE column were better. The results indicated that MISPE column was better than C18–SPE.