表面增强拉曼光谱法快速检测猪肉中左旋咪唑残留

左旋咪唑是一种广谱抗虫药，被广泛应用于抗猪、牛等牲畜体内的线虫。同时左旋咪唑具有特殊的免疫调节作用，在动物养殖中常用于抗菌消炎、抗病毒、促生长等方面。当其被不合理使用时容易在禽畜肉中产生残留，目前常见的左旋咪唑检测方法为液相色谱法与气相色谱法，该类方法具有操作复杂、耗时长、成本高等缺点。表面增强拉曼光谱法具有分析速度快、检测灵敏度高和特异性好等优点，近年来被广泛应用于农残、兽残等物质的快速检测。为实现猪肉中左旋咪唑残留的快速检测，建立了一种猪肉中左旋咪唑残留的表面增强拉曼光谱快速检测方法。通过单因素实验，确定了金胶与样品溶液最佳体积比和最适积分时间分别为2∶1与20 s。通过比较不同萃取方法与萃取溶剂对猪肉中左旋咪唑盐酸盐残留量的提取效果，确定了正己烷液液萃取后离心、取上清液氮吹复溶的操作简单、耗时短的提取条件。通过密度泛函理论中B3LYP/6-311+G(d)基组对左旋咪唑盐酸盐理论光谱进行计算，在优化分子结构后进行频率与拉曼光谱计算，所得理论计算光谱与固体光谱、溶液光谱出峰情况具有较好的一致性。根据理论计算光谱、固体光谱与溶液光谱确定左旋咪唑盐酸盐的SERS特征峰并进行振动归属，得到469，627和969 cm-1处特征峰作为左旋咪唑盐酸盐的定量特征峰，其中469 cm-1为C—S键伸缩振动，627 cm-1为苯环C—C弯曲变形振动，969 cm-1为咪唑环面内弯曲和侧链骨架振动。在最佳实验条件下，建立了左旋咪唑盐酸盐标准溶液特征峰SERS信号与浓度的标准曲线，线性方程R2值均在0.9以上。对不同加标浓度的实际样品进行检测，得到平均回收率为80.39%~95.94%，RSD值为3.08%~6.20%。该法操作简便、稳定性好，无需对样品进行复杂的预处理即可实现对猪肉中左旋咪唑残留的快速准确测定。

Rapid Detection of Levamisole Residue in Pork by Surface Enhanced Raman Spectroscopy

Levamisole is a broad-spectrum anti-insect drug widely used to fight against nematodes in pigs, cattle and other livestock. Meanwhile, levamisole has a special immunomodulatory effect often used in anti-bacterial, anti-inflammatory, anti-virus and growth-promoting aspects in animal breeding. When it is used irrationally, it is easy to produce residues in poultry meat. At present, the common detection methods of levamisole are liquid chromatography and gas chromatography, which have the disadvantages of complex operation, long time consumption and high cost. Surface-enhanced Raman spectroscopy (SERS) has the advantages of fast analysis speed, high detection sensitivity and good specificity and has been widely used in the rapid detection of pesticide residues and animal residues in recent years. In order to realize the rapid detection of levamisole residues in pork, a rapid detection method of levamisole residues in pork by SERS was established. Through a single factor experiment, the optimal volume ratio of gold colloid to sample solution and the optimal integration time are determined to be 2∶1 and 20 s, respectively. By comparing the extraction effects of different extraction methods and solvents on the residual levamisole hydrochloride in pork, the extraction conditions of centrifugation after liquid-liquid extraction with n-hexane and redissolution with nitrogen blowing were determined. The theoretical spectrum of levamisole hydrochloride was calculated by B3LYP/6-311+G(d) basis set in density functional theory. After optimizing the molecular structure, the frequency and Raman spectrum was calculated. The theoretically calculated spectrum was in good agreement with the peaks of the solid spectrum and solution spectrum. According to theoretical calculation spectrum, solid spectrum and solution spectrum, SERS characteristic peaks of levamisole hydrochloride are determined, and vibration attribution is carried out. The characteristic peaks at 469, 627 and 969 cm-1 are obtained as characteristic quantitative peaks of levamisole hydrochloride, in which 469 cm-1 is C—S bond stretching vibration, 627 cm-1 is benzene ring C—C bending deformation vibration, and 969 cm-1 is imidazole ring in-plane bending and side chain skeleton vibration. Under the optimum experimental conditions, the standard curve of SERS signal and levamisole hydrochloride standard solution concentration was established, and the R2 values of linear equations were all above 0.9. The average recovery of levamisole hydrochloride with different spiked concentrations was 80.39%~95.94%, and RSD was 3.08%~6.20%. The method is stable and straight forward and can be used for rapid and accurate determination of levamisole residues in pork without complex pretreatment.