Application of Chemometrics to NIRS Determination of TNT in Composite Explosive

To establish mathematical model correlating the analyte (TNT) in the explosive samples with their near infrared spectra, a total of 155 samples collected directly from the production line and self-prepared in the same way were taken, and their NIR spectra were taken with the abnormal spectra rejected according to the values of SpecResF found. 63 samples among the 155 were selected at random as the calibration set and the remainder (92 samples) were taken as the testing set. All these samples were analyzed by the conventional NIRS method with solvent extraction, to obtain values of TNT used as reference in modelling. Based on the NIRS data, PLS was applied to establish mathematical models, selecting the following optimum modelling wavelength sections:9 114.1-8 331.2 cm^-1, 7 671.6-7 189.5 cm^-1, 6 514.5-5 666 cm^-1, 5 102.8-4 929.3 cm^-1 and 4 744.14-4 728.71 cm^-1. Optimal models were selected through cross testing of RMSECV and considering the ideal of the curve of RMSECV/dimension and results of PCA of the spectra. Precision and accuracy of the proposed method were evaluated by applying the χ²-testing, and on the base of values of predictive standard deviation (SEP) and Bias values. 8 samples with TNT contents in the range from (w) 36.5% to 41.9% were analyzed by the proposed new method, giving value of Bias of 0.078% and SEP% of 0.514%. In addition, no organic solvent was used in the new method.