Detection of Cocaine and its Impurities in Fingernails Using Palm-sized Near-infrared Spectroscopy and Machine Learning Analytics

Fingernails are a non-invasive alternative biological matrix to blood and urine specimen, which are often considered, invasive, intrusive and can be easily adulterated. Additionally, fingernails have shown the ability to accumulate drugs over a larger period, making them a suitable biological matrix for identifying chronic drug exposure. Near-infrared spectroscopy (NIR) is a portable instrument that offers rapid analysis of drugs and their impurities, specifically their physical properties including particle size, compaction density and polymorphs. This information is advantageous as it allows differentiation between samples composed of the same chemical identity but of different sources/grades. For example, NIR spectroscopy has the protentional to identify chronic vs acute drug exposure, which is useful for evidence in court when dealing with possession with intent to supply. This work utilised NIR spectroscopy for the analysis of fingernails spiked with cocaine hydrochloride (HCl) and its impurities being: benzocaine, calcium carbonate, diltiazem HCl levamisole HCL, lidocaine HCl and procaine HCl. NIR spectroscopy was paired with principal component analysis to identify unique patterns within the sets of spiked fingernails. While some fingernails created their own distinct group (e.g. calcium carbonate), drugs such as lidocaine HCl and procaine HCl were grouped together. This was attributed to these drugs sharing similar chemical structures. Key NIR bands were identified cocaine HCl at 1143 nm (C-H stretch second overtone) related to their aromatic structure, 1180 (C-H stretch second overtone) related to their CH3 group, 1000-1100 (second overtone) related to their N-H groups and 1400 – 1600 (region first overtone) related to N-H and O-H groups. Findings showed that NIR spectroscopy identified the presence of cocaine HCl and its impurities within fingernails