Quantitative analysis of the water of crystallization of gypsum by near-infrared spectroscopy in Yungang Grottoes

Near infrared spectroscopy is considered to be an effective analytical tool which is used in various fields, however, it is rarely used in the analysis of the water of crystallization of rocks from stone relics. In the present study, a calibration model was developed for the non-destructive estimation of the water of crystallization content of dihydrate gypsum in rocks using Fourier transform near infrared spectroscopy. A total of 51 samples were prepared in the laboratory to simulate the actual samples from Yungang Grottoes, their Fourier transform near infrared spectra were correlated to the water of crystallization content by means of partial least square regression, and then the calibration model was developed. 5 actual samples from Yungang Grottoes were analyzed by X-ray diffraction and X-ray fluorescence. The optimal model was achieved with a correlation coefficient of 0.9899 and a root mean square error of cross validation of 0.2190, and the correlation coefficient and the root mean square error of the prediction of the validation set were 0.9834 and 0.4558, respectively.