基于激光拉曼光谱归一化法的乙醇定量分析研究

Quantitative Analysis of Ethanol Based on Laser Raman Spectroscopy Norm alization Method

拉曼光谱具有分辨率高、分析速度快、检测样品制备简单、无损以及可在线测量等优点,被广泛用于分析物质的成分与分子结构信息,可以对多种有机物和无机物进行定性和定量的分析。目前主要应用多以相对比较成熟的定性分析为主,用于定量分析时,一方面由于拉曼光谱的重现性较差,会受到很多内部因素干扰;另一方面,拉曼光谱的分析理论相比于传统技术还不够完善,分析结果的误差较大,限制了其在定量分析中的应用。在基于强度比值的定量分析中,拉曼强度归一化理论的出现为拉曼光谱的应用提供了理论依据,参考峰/内标峰及拟合方法的选择对测量准确性和稳定性有较大的影响。采用激光拉曼系统研究了不同浓度乙醇溶液拉曼光谱特征峰(C—C—O对称伸缩,874 cm^(-1))与其他参考峰/内标峰的相对强度关系,分别提出了基于乙醇本征峰位比值法和基于CCl_(4)特征峰位的内标法,建立了线性回归分析模型,经归一化处理后两种方法均可有效消除系统中的突变噪声及强荧光背景的影响。通过联合假设检验等统计学方法对比了不同组内与组间的数据差异,确定了两种方法中准确性和稳定性最好的参考峰/内标峰。F检验与t检验表明,用乙醇自身峰位比值法进行标定时,以1 446 cm^(-1)(CH_(3)-不对称变形)处特征峰为参考峰建立的标准曲线能更为准确地反演乙醇的浓度;用CCl_(4)作为内标物时,以446 cm^(-1)处拉曼特征峰为内标峰时的标准曲线具有更高的稳定性和准确度。30 d内进行二次复测量时无需进行标准曲线的再次测量与绘制,避免了重复的定量分析实验以及后期数据处理过程对时间的消耗。根据不同标定方法建立的线性回归模型能够为乙醇溶液浓度的定量分析提供实验依据,通过该模型在乙醇溶液浓度检测系统中的应用,可以较为精确地实时反演乙醇浓度,从而实现对具有强荧光背景干扰的高浓度范围的乙醇溶液准确、快速、实时的定量分析。

Raman spectroscopy has the advantages of high resolution,fast analysis,simple sample preparation,nondestructive,online measurement,etc.It is widely used to analyze the composition and molecular structure information of a wide range of organic and inorganic substances for qualitative and quantitative analytical measurement.At present,it is mainly used for quantitative analysis.When used for quantitative analysis,the poor reproducibility and the imperfect analysis theory of Raman spectroscopy are two main factors that limit its application.In the quantitative analysis based on intensity ratios,the emergence of Raman intensity normalization theory has provided a theoretical basis for its application.The choice of the reference peak/internal standard peak and the fitting method have a great influence on the measurement accuracy and stability.In this paper,the relative intensities of the characteristic peaks(CC-O symmetrical stretching,874 cm^(-1))of the Raman spectra of ethanol and other reference/internal standard peaks with different ethanol concentrations were investigated using a laser Raman system.A peak ratio method based on ethanol intrinsic peak and an internal standard method based on the characteristic peak position of CCl_(4) were developed,and both methods can effectively eliminate the effects of mutation noise and strong fluorescence background in the system through normalization.The reference peak/internal standard peak with the best accuracy and stability of the two methods was determined by statistical methods such as joint hypothesis testing for data differences within and between different groups.The F-test and t-test showed that the standard curve established with the characteristic peak at 1446 cm^(-1)(CH_(3)-asymmetric deformation)as the reference peak could more accurately invert the concentration of ethanol when the calibration was performed by the self-peak ratio method,while the standard curve with the Raman characteristic peak at 446 cm-as the internal standard peak had higher stability and accuracy when CCl_(4) was used as the internal standard.The retest within 30 days eliminates the need to measure and plot the standard curve again.The linear regression model established according to the two calibration methods can provide an experimental basis for the quantitative analysis of ethanol solution concentration.The ethanol concentration can be inverted more accurately in real-time,through the application of the model in the ethanol solution concentration detection system,to achieve accurate,rapid and real-time quantitative analysis of ethanol solutions in the high concentration range with strong fluorescence background interference.