LU Mei-hong1, GONG Peng2, ZHANG Fan1, WANG Zhi-jun1, FENG Duo1，MENG Tian-hua3
1. Department of Electronic Information and Physics, Changzhi University, Changzhi 046011, China
2. College of Science, University of Shanghai for Science and Technology, Shanghai 200093, China
3. School of Physics and Electronics Science, Shanxi Datong University，Datong 037009, China
Abstract：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.
Key words：EDTA-2Na; THz spectrum; Raman spectrum; Density functional theory
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