Abstract
Accurate identification and quantification of methamphetamine (MA) and its related substances are essential for the investigation and fair trial of drug offenses. In this study, a modified LC-ESI-MS/MS method for the simultaneous determination of MA and its isomer N-isopropylbenzylamine (N-IBA) in forensic samples was developed and validated. Optimum chromatographic separation of the target analytes was achieved on an Agilent Poroshell 120 SB-C18 column ( 4.6 × 100 mm, 2.7 μm) at 40°C with isocratic elution at the flow rate of 0.40 mL/min. The mobile phase was acetonitrile and 20 mM ammonium acetate solution containing 0.1% formic acid (80 : 20, v / v ). Positive ESI-MS/MS detection was performed in multiple reaction monitoring (MRM) mode to identify and quantify the target analytes. Method validation showed excellent linearity in the range of 0.51 ng/mL~51 ng/mL for MA and N-IBA. The low limit of detection (LLOD) and low limit of quantification (LLOQ) reached 0.1 ng/mL and 0.3 ng/mL for both analytes. The method showed a satisfactory accuracy with an inter- and intraday-relative error (RE) <20%, and a precision of inter- and intraday relative standard deviation (RSD) less than 15%. The validated method was successfully applied in real forensic samples and resulted in the detection of MA and N-IBA in 8 suspected samples in drug cases that only deemed MA positive using our previous routine screening procedure, which avoided the misidentification of N-IBA as MA.
Highlights
Drug abuse has been increasingly becoming one of the most severe social problems all over the world
According to the structural data, N-IBA is an isomer of MA, normally exhibiting similar patterns of collision-induced dissociation (CID)
The mass spectra for MA and N-IBA were obtained in full-scan MS and MS/MS mode
Summary
Drug abuse has been increasingly becoming one of the most severe social problems all over the world. Accurate identification and quantification of MA in the forensic samples is important for investigations and fair trials of drug crimes [12]. An isomer of MA, called Nisopropylbenzylamine (N-IBA), has often been used as the adulterant of MA in drug crimes due to their high similarity in structure (Figure 1), which resulted in the misidentification of N-IBA as MA in suspected samples [13]. The forensic science laboratory of the United States Drug Enforcement Administration (DEA) reported several cases of counterfeiting MA hydrochloride with N-IBA hydrochloride from 2007 to 2008 [14]. Since 2011, the material identification center of the Ministry of State Security of the People’s Republic of China has reported several drug cases that N-IBA hydrochloride was mixed with MA
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