Abstract：As an in-situ, fast and noninvasive mid-infrared spectroscopy technology, ATR-FTIR has been increasingly applied in many engineering fields, particularly in in-situ real-time measurement of the solution concentration during a crystallization process. Water is a common solvent for crystallization, which has very strong absorption peaks in the mid-infrared range but has different spectra absorbances under different temperature. Thus, the affects from water and its temperature could not be ignored in measuring the solution concentration in the mid-infrared range. Based on the Lambert-Beer’s law, it is proposed in this paper to subtract the pure solvent spectra from the solution spectra under the same temperature to accurately measure the solution concentration. Take the L-glutamic acid (LGA) solution as a case for illustration. Three calibration models were established for comparison by using the original spectra of LGA aqueous solution, the original spectra deducted uniformly by the water spectra under room temperature (25 ℃), and the solution spectra deducted by the water spectra and measured under the same temperature, respectively. The results demonstrated that the proposed temperature-related differential spectra measurement method could effectively eliminate the influence of solvent on the spectra. The proposed method has a referential value for improving in-situ ATR-FTIR spectra measurement accuracy in practice.
Key words：Disturbance of water absorbance peak; Quantitative analysis; In-situ measurement; Solution concentration; ATR-FTIR; Crystallization
[1] CHU Xiao-li(褚小立). Molecular Spectroscopy Analytic of Technology Combined with Chemometrics and its Aplications (化学计量学方法与分子光谱分析技术). Beijing: Chemical Industry Press(北京：化学工业出版社), 2011.
[2] HUANG Hong-ying, YIN Qi-he(黄红英，尹齐和). Journal of the Graduates of Sun Yat-sen University·Natural Science·Medicine(中山大学研究生学刊·自然科学·医学版)，2011，32: 20.
[3] Nagy Z K, Braatz R D. Annual Review of Chemical and Biomolecular Engineering，2012，3: 55.
[4] Simon L L, Pataki H, Marosi G, et al. Organic Process Research & Development，2015，19: 3.
[5] Togkalidou T, Fujiwara M, Patel S, et al. Journal of Crystal Growth，2001，231: 534.
[6] Chen Z, Lovett D, Morris J. Journal of Process Control，2011，21: 1467.
[7] Zhang F, Liu T, Wang X Z, et al. Journal of Crystal Growth，2017，459: 50.
[8] Olchowicz J C, Coles D R, Kain L E, et al. Journal of Chemical Education，2002，79: 369.
[9] Powell J R, Wasacz F M, Jakobsen R J. Applied Spectroscopy，1986，40: 339.
[10] Kee N C S, Tan R B H, Braatz R D. Crystal Growth & Design，2009，9: 3044.
[11] BAI Sha-sha, WANG Huan, CHEN Yu-jing, et al(白沙沙，王 欢，陈玉静，等). Spectroscopy and Spectral Analysis(光谱学与光谱分析)，2015，35(3)：894.
[12] Zhang F, Liu T, Huo Y, et al. Journal of Crystal Growth，2017, 469: 136.
[13] WENG Shi-fu(翁诗甫). Fourier-Transform Infrared Spectral Analysis (傅里叶变换红外光谱分析). Beijing: Chemical Industry Press(北京：化学工业出版社)，2009.
[14] WANG Hui-wen(王惠文). Partial Least Squares Regression Method and Application(偏最小二乘回归方法及其应用). Beijing: National Defence of Industry Press(北京：国防工业出版社), 1986.
[15] Schrader B. Infrared and Raman Spectroscopy: Methods and Applications. John Wiley & Sons, 2008.
[16] Chianese A, Kramer H J M, Industrial Crystallization Process Monitoring and Control，Germany: Wiley-VCH，2012.
