Performance Comparison of Ambient Ionization Techniques Using a Single Quadrupole Mass Spectrometer for the Analysis of Amino Acids, Drugs, and Explosives

The utilization of ambient ionization (AI) techniques for mass spectrometry (MS) has significantly grown due to their ability to facilitate rapid and direct sample analysis with minimal sample preparation. This study investigates the performance of various AI techniques, including atmospheric solids analysis probe (ASAP), thermal desorption corona discharge (TDCD), direct analysis in real time (DART), and paper spray coupled to a Waters QDa mass spectrometer. The focus is on evaluating the linearity, repeatability, and limit of detection (LOD) of these techniques across a range of analytes, including amino acids, drugs, and explosives. The results show that each AI technique exhibits distinct advantages and limitations. ASAP and DART cover high concentration ranges, which may make them suitable for semiquantitative analysis. TDCD demonstrates exceptional linearity and repeatability for most analytes, while paper spray offers surprising LODs despite its complex setup (between 80 and 400 pg for most analytes). The comparison with electrospray ionization (ESI) as a standard method shows that ambient ionization techniques can achieve competitive LODs for various compounds such as PETN (80 pg ESI vs 100 pg ASAP), TNT (9 pg ESI vs 4 pg ASAP), and RDX (4 pg ESI vs 10 pg ASAP). This study underscores the importance of selecting the appropriate ambient ionization technique based on the specific analytical requirements. This comprehensive evaluation contributes valuable insights into the selection and optimization of AI techniques for diverse analytical applications.