## 3 Results and Discussion  
### Method Comparison  
One major parameter for a comparison is the possibility to detect target compounds. For the investigated target compounds there is a clear trend for the three investigated methods. IDTs are only capable of detecting compounds that they are specifically made for. In this case, amphetamine, methamphetamine, and MDMA. Compared to IDTs, IMS systems are more flexible and allow to detect a broader range of analytes. The ability to ionise target compounds is the main limitation for IMS systems, valid for, e.g., BMK. In this study, all target compounds had been detected successfully with APLD-MS. Like IMS, MS is limited to analytes that can be ionised. Due to the utilized chemical ionisation method, this technique is capable to analyse a wide variety of substances. This leads to the observation, that the APLD-MS can detect the highest number of compounds. The parameter selectivity is of interest as well as it influences the possible field of application. While IDTs are made to investigate if a number of target compounds are present, no information can be gathered on what specific substance triggered a positive signal. In addition, every new target compound that should be investigated needs a new IDT. In theory, IMS is capable to distinguish different possible substances. Practically, the low resolution of most IMS makes it difficult to distinguish between similar compounds and for the same reason, the presence of multiple substances can be an issue, too. In contrast to IDTs, IMS libraries can be updated to detect new target compounds. The most selective system in this study, even for multiple substances present, is the APLD-MS. It allows identifying target compounds and even unknown substances can be presumed, based on the mass spectra. Another major parameter is the complexity of the analytical technique and its user requirements. IDTs are very compact, cheap, easy to handle and require only knowledge about possible cross-reactions and contraindications. IMS in comparison, needs significant set-up time previous to a measurement, is considerably larger, orders of magnitude more expensive in acquisition, and needs trained personal for operation. In addition, many IMS utilise a Ni63-source and thus may require radiation protection trained personal. As many on-site measurements were done for target compounds that can be found in a system-integrated library, result interpretation is done by the device, and hence no addition training is needed for the operator. APLD-MS needs a well-trained operator, electricity and pressurised gases. Its set-up time is higher compared to IMS and the operator's knowledge needs to be the highest of all three methods. The operators training is neededfor performing measurements as well as interpreting obtained results. Therefore, APLD-MS is the most sophisticated system that was investigated. In addition to the above discussed set-up time, duration per measurement, as another parameter, is especially relevant for larger operations and time critical activities. According to the conducted experiments, the highest sample throughput is achievable for IMS. It took about eight seconds to perform one measurement. APLD-MS needed about 30-60 s to obtain results. The longest time was necessary for the IDT. About three minutes passed before the enzymatic reaction was concluded. Depending on the sample number and available staff, parallel testing could decrease this time to a certain extent and change the necessary total time. These results imply, that the sample amount was adequate and no overload occurred. This overload is imaginable for real samples with unknown concentration, especially at on-site measurements. This additional cleaning affects only IMS and APLD-MS because IDTs are only used once. In addition, the possibility of IDTs to analyse two or more drugs at once should be mentioned as well. All mentioned aspects can be transformed into eight key parameters that can be compared for the investigated techniques.