Direct quantitative analysis of cocaine by thin layer chromatography plus a mobile phone and multivariate calibration: a cost-effective and rapid method
The detection and quantification of trace amounts of illicit substances such as crack-cocaine continues to be important for law enforcement and clinical medicine. Conventional methods available for crack-cocaine and adulterant detection include chromatography and presumptive testing. Here, we report a simple and inexpensive approach that employs a cell phone which images of thin-layer chromatography (TLC) plates were acquired to directly quantify cocaine and phenacetin in illicit samples seized in Brazil from 2012. Integration of a mobile application with a cell phone enabled immediate processing of TLC results, which eliminated the need for a bulky and expensive spectrometer. Partial least squares (PLS) regression was built using the RGB image system from the TLC plates containing cocaine (0.50 to 16.00 mg mL−1) and phenacetin (0.00 to 14.00 mg mL−1) as adulterants, acquired from a cell phone camera. The RMSEP values obtained for cocaine and phenacetin models were, respectively, equal to 1.60 and 1.36 mg mL−1, and their precision was respectively equal to 6.22 and 7.14%. No statistical difference was observed at a confidence level of 95% for both analytes calculated by the proposed method and those found by the reference method using gas chromatography with flame ionization detection (GC-FID), proving the reliability of the imaging method as an alternative approach for these assays.