| Shanxi aged vinegar is one of the geographical indication products in Shanxi Province.Because of its unique production process,flavor and nutritional value,it is welcomed by everyone.It has the reputation of“the best vinegar in the world”and it is listed as a national intangible cultural heritage.At present,the blended vinegar or Shanxi vinegar of non-geographical signs posing as Shanxi old vinegar is still happening.Tetramethylpyrazine is one of the characteristic components in Shanxi old vinegar.It has antithrombotic,antitumor,and protective effects on the human digestive and respiratory light system.With the extension of storage time,the content of Ligustrazine increase gradually.The current methods for the detection of tetramethylpyrazine are mainly high-performance liquid chromatography,ultraviolet spectrophotometry,nuclear magnetic resonance,near-infrared spectroscopy and so on.Although the detection results of traditional instrument are accurate,it is not suitable for on-site high-volume rapid screening because of heavy instrument,complicated operation,and the long detection period.The portable laser Raman detector is compact,easy to operate,and its speed is fast.It is very suitable for the law enforcement department to use in the heavy routine test.In this study,a method for the Raman rapid detection of Shanxi aged vinegar based on tetramethylpyrazine was established.First,the Shanxi aged vinegar was pretreated.By comparing the Raman spectra of 1 mg/mL tetramethylpyrazine standard solution,vinegar sample,and vinegar sample respectively added 0.1 mg/mL,0.2 mg/mL,and 0.5mg/mL hydrochloric standard solution?volume ratio of 1:1?,the characteristic peak is preliminarily determined.Then the theoretical Raman spectra of Ligustrazine are calculated with the theory of quantum chemistry,and compared,the Raman characteristic peak of tetramethylpyrazine was further determined as the Raman shift 1599 cm-1.Secondly,the parameters of the surface-enhanced Raman spectroscopy method for measuring the tetramethylpyrazine in Shanxi aged vinegar are optimized,including the integration time,the number of integration,the smoothing coefficient,the detection power,and the sample amount.The optimization results are as follows:the integration time is 20 s.The number of integrations is 10.The smoothing coefficient is 10.The power is 300 mW.And the sample volume is 20?L.There are the best experimental conditions for Raman rapid detection established in this study.Finally,the method for the detection of Shanxi aged vinegar established with the optimized conditions,and it was evaluated from the three aspects of precision,repeatability,and added recovery rate.The Raman spectroscopy precision RSD was between 2.3%and 3.6%,the reproducibility RSD was between 1.6%and 3.2%,the spike recovery was between 80.5%and 87.2%,and the coefficient of variation was between 5.1%and 9.8%.between.HPLC precision RSD was between 1.2%and 2.8%,spike recoveries were between88.7%and 93.2%,and coefficients of variation ranged from 4.4%to 6.1%.The results showed that the precision and reproducibility of surface-enhanced Raman rapid detection method were good.The coefficient of variation of the method was less than 10%when the spiked amounts were0.025 mg/mL,0.05 mg/mL,and 0.1 mg/mL respectively,and the method was satisfactory for rapid laboratory and field testing. |
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