乙二胺四乙酸二钠简称EDTA-2Na, 是一种含有羧基和氨基的螯合剂, 具有广泛的配位性能。 由于EDTA-2Na几乎能与所有的金属离子形成稳定的水溶性络合物, 其络合作用可以消除由金属离子引起的食品变浊、 变质、 变色及维生素C的氧化损失, 从而对食品起到护色、 稳定、 抗氧化和保鲜的作用, 因而作为一种护色剂、 品质改良剂和协同抗氧化剂, 常被广泛添加到食品当中。 但是, EDTA-2Na的过量或不当使用会危害人体健康, 甚至引起暂时性血压下降、 肾脏障碍等, 所以一种快速检测EDTA-2Na的方法的提出对于食品安全尤为重要。 相对于传统检测方法过程繁杂、 耗时耗力的特点, 太赫兹时域光谱技术及拉曼光谱技术对EDTA-2Na具有良好的指纹特性, 安全快速的检测优点使其具有较大的应用潜力。 目前, 用太赫兹光谱技术及拉曼光谱技术对EDTA-2Na检测的理论与实验研究还未见报道。 利用太赫兹时域光谱技术和拉曼光谱技术对EDTA-2Na结晶粉末进行检测研究, 获得了样品在0.2～2.6 THz范围的特征吸收及10～4 000 cm-1的拉曼散射谱; 基于密度泛函理论, 利用B3LYP/6-31G*基组优化并计算EDTA-2Na分子的振动频率, 对其太赫兹吸收峰和拉曼散射峰对应的振动模式进行了归属和解析。 结果表明, EDTA-2Na在0.88, 1.40, 1.73和2.32 THz; 在921, 963, 990, 1 081, 1 336, 1 428和1 614 cm-1处分别有明显的THz吸收峰和拉曼特征峰, 这些振动频率与实验结果吻合较好, 可以作为鉴定和检测的特征峰。 特别地, 对6.7～85.8 cm-1（0.2～2.6 THz）范围内的低频拉曼光谱和太赫兹光谱进行对比, 结合密度泛函理论对特征峰产生机理进行解析, 结果显示太赫兹光谱和低频拉曼光谱之间有很强的互补性和一致性, 可以作为光谱技术检测EDTA-2Na的有效互补手段, 结果可靠。 该研究为食品添加剂乙二胺四乙酸二钠的太赫兹光谱及拉曼光谱特征峰数据库的建立提供了实验参考, 也为利用密度泛函理论预测其光谱特征提供了理论依据。

Disodium ethylenediaminetetraacetate (EDTA-2Na) is a chelating agent containing carboxyl and amino groups, which has a wide range of coordination properties. EDTA-2Na is often widely added to food as a color protection agent, quality improver and synergistic antioxidant. However, the excessive or improper use of EDTA-2Na will harm human health; even cause temporary blood pressure drop, kidney disorders, etc. Therefore, it is necessary to propose a rapid method of food EDTA-2Na detection. The process of the traditional detection method is complex, time-consuming and labor-consuming. THz time-domain spectroscopy and Raman spectroscopy have good fingerprint characteristics for EDTA-2Na. The advantages of safe and fast detection make it have great application potential. At present, the theoretical and experimental study of EDTA-2Na detection by THz-TDS and Raman spectroscopy has not been reported. EDTA-2Na crystalline powder was detected for the first timer by using THz time domain spectroscopy and Raman spectroscopy. The characteristic absorption and Raman scattering spectra of EDTA-2Na crystal powder in 0.2～2.6 THz band and 10～4 000 cm-1 band were obtained. Based on density functional theory, the vibration frequency of EDTA-2Na molecule was optimized and calculated by B3LYP/6-31G* group. The corresponding vibration modes were assigned and analyzed. The results showed that there is obvious terahertz vibration absorption at 0.88, 1.40, 1.73 and 2.32 THz for EDTA-2Na, which is basically consistent with the abnormal dispersion frequency of the refractive index spectrum. Moreover, there are obvious Raman characteristic peaks at 921, 963, 990, 1 081, 1 336, 1 428 and 1 614 cm-1, which are in good agreement with the experimental results and can be used as the characteristic peaks for identification and detection. In particular, the low-frequency Raman spectrum and THz spectrum in the range of 6.7～85.8 cm-1 (0.2～2.6 THz) were compared, and the mechanism of characteristic peaks generation was analyzed with density functional theory. The results showed that there is a strong complementarily and consistency between THz spectrum and low-frequency Raman spectrum, which can be used as an effective complementary means of spectrum technology to detect EDTA-2Na, and the results were reliable. The study provides experimental reference and theoretical basis for the detection of food additive EDTA-2Na and the establishment of the database.