The recovery and detection of trace methamphetamine residues deposited on laboratory coat materials

Illicit drugs handling and processing could potentially contaminate the surfaces and personal protection equipment used by the analysts in drug testing laboratories. Such drug contamination, if any, might lead to long-term harmful exposure. Therefore, the monitoring of possible contamination is crucial to reduce the harmfulness resulted from the exposures. Using methamphetamine as a contamination indicator, this study aimed to recover and detect trace methamphetamine residues deposited on the laboratory coat material. In this study, methamphetamine was chosen as the target substance due to its high prevalence of seizures in Malaysia which is often ended up in the forensic laboratory for analysis. A dispersive liquid-liquid microextraction (DLLME) procedure was firstly optimised, followed by the derivatisation of methamphetamine using trifluoroacetic acid anhydride and finally the detection by gas chromatography-mass spectrometry (GC-MS) method. Known concentrations of methamphetamine were deposited on seven types of laboratory coat materials, and their recovery percentages were then determined and compared. Based on the response surface methodology optimisation, DLLME procedure utilising 685 μL dichloromethane as extraction solvent and 1000 μL 2-propanol as disperser solvent in combination with vortexing for 90 seconds and centrifugation at 500 rpm for 5 minutes was used for the recovery of methamphetamine from fabric substrate. Derivatised methamphetamine was found to provide enhanced responses for the detection of trace methamphetamine through the application of validated GC method (linearity: y= 0.0017 x - 0.4698, R2= 0.9993; limit of detection: 7.80 ng/mL; limit of quantification: 23.40 ng/mL; intra-day precision: 3.35 - 3.76%; inter-day precision: 4.65 - 6.50%; accuracy: 94.92% - 106.01%). The presence of methamphetamine was also confirmed through the comparison and matching with mass spectral database. Percentage recoveries of methamphetamine from seven types of laboratory coat materials were determined to be more than 45% at three different concentration levels covering 0.5, 1.5, and 3 μg/100 cm2. To conclude, this study had successfully recovered and detected the trace methamphetamine residues deposited on laboratory coat materials based on the proposed DLLME-GC-MS procedure