<b>Rapid quantitative analysis of methamphetamine by portable near-infrared </b><b>spectroscopy and PLS modelling</b>

For rapid on-site detection of methamphetamine, a portable NIRspectrometer was used to model and analyze the collected samples.Transmission spectra (908-1676 nm) of 359 methamphetamine crystal samples and 187 methamphetamine tablet samples were collected, first-order derivatives and the S-G smoothing method were applied for spectral preprocessing. The partial least squares (PLS) method was used for modeling, and the quantitative models for methamphetamine crystals were 2.10%, 2.12% and 2.19% for RMSECV, RMSEV and RMSEP, respectively; in contrast, RMSECV, RMSEV, and RMSEP of methamphetamine tablets were 0.78%, 0.80%, and 0.82%, respectively. The results of the internal cross-validation and the methodology review showsthat the measurements of the modelled results are consistent with the true values, and that the model has good stability and can be used for accurate field measurements. Therefore, real-time sample analysis using portable NIR technology combined with chemometric modeling in crime scene investigation has become an inexpensive, rapid and reproducible analytical method, which helps the police to determine the quality of drugs in a timely manner for case analysis.