Objective To identify the retention time of semen(stains)inside and outside the cadaver using Fourier Transform Infrared(FTIR)spectroscopy and chemometrics.Methods A simulated environment inside the porcine vagina was used to retain fresh semen for 0～168 hours inside and outside the body.Infrared spectroscopy data were collected,and chemometric methods including Principal Components Analysis(PCA)and Partial Least Squares(PLS)regression models were established.Results The infrared spectrum peak positions of semen(stains)inside and outside the body did not show significant changes over time.The PCA results showed good clustering relationships,and the predicted deviation value in the PLS regression model was 15.786 3 hours,with an R2 value of 0.922 4.The characteristic wavenumbers selected by the CARS algorithm were in the wavelength ranges of 1 000～1 180 cm-1,1 430～1 480 cm-1,and 1 700～1 760 cm-1.Conclusion Fourier Transform Infrared spectroscopy has the potential to identify the retention time of semen(stains)inside and outside the body,and there are differences in the degradation trends of semen(stains)inside and outside the body.

Objective To distinguish Khat from its similar plants,such as white tea and Houttuynia cordata,so as to identity Khat and its camouflage and confusing products in smuggling crime and public security anti-drug work.Methods FTIR is used to collect the infrared spectral data of plant samples,and the data are analyzed by chemometrics.The original data were preprocessed by three data processing methods,namely,SG smoothing,baseline and normalization,then the processed data were classified and reduced by PCA,finally the mathematical model was constructed by three methods:KNN,RF and SVM for classification and prediction.Results The results were expressed by confusion matrix,and the accuracy of the RF model is 96.51%.The accuracy of the SVM model is 98.84%;The accuracy of the KNN model is 93.02%.Conclusion In this experiment,FTIR was used to establish a model for rapid identification of Khat grass,the SVM model has the highest correct recognition rate and good parameters,which can be used to distinguish dry khat from its similar plants.