RAPID QUANTITATIVE ANALYSIS OF METHAMPHETAMINE BY PORTABLE NEAR-INFRARED SPECTROSCOPY AND PLS MODELING

To rapidly detect different types of methamphetamine in the field, a portable near infrared spectroscopy (NIR) method was used to model and analyze the collected samples. Transmission spectra of 359 methamphetamine crystal samples (content range of 7.5-99.4%) and 187 methamphetamine tablet samples (content range of 2.43-23.91%) were collected, first-order derivatives and the Savitaki-Golay smoothing method were applied for spectral preprocessing. The drug concentrations in the calibration and validation sample sets were analyzed using high-performance liquid chromatography. The partial least squares quantitative analysis models were built, and the quantitative models for methamphetamine crystals were 2.10, 2.12 and 2.19% for root mean square error of cross-validation (RMSECV), root mean square error of validation (RMSEV) and root mean square error of prediction (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 show that the measurements of the modeled 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 can be performed using NIR technology combined with chemometric models, which helps the police to determine the quality of drugs in a timely manner for case analysis.