Evaluation of an Internal Standard for Qualitative DART-MS Analysis of Seized Drugs

Rapid and accurate screening tools for seized drug analysis continue to be needed due to the complexities associated with the emerging drug landscape. Direct analysis in real-time mass spectrometry (DART-MS) is one technique that has been used for this purpose and is seeing increased implementation due to its ability to provide high-fidelity information rapidly. As with any analytical technique, ensuring data integrity with DART-MS results is critical. To further enhance data integrity and eliminate some of the challenges associated with qualitative analysis of seized drugs using DART-MS, the incorporation of an internal standard was investigated. After evaluating a number of candidate compounds, tetracaine was chosen because of its desirable characteristics. An appropriate concentration of tetracaine was established that provided similar sensitivity to GC-MS for a panel of drugs. The presence of tetracaine in a drug extract was found to cause a reduction in signal for some common drugs due to competitive ionization but did not cause complete suppression of signal at relevant concentrations. Evaluation of a set of 60 representative case samples with and without internal standard found that the presence of internal standard did not negatively impact the results and that its presence eliminated the false identification of noise peaks in negative samples. The use of an internal standard also provided within-sample mass calibration and analyte concentration checks. It also allowed for automated mass drift compensation, removing a time-consuming process for high resolution DART-MS data processing.