Solving problems in ion mobility measurements of forensic samples with thermal desorption and dynamic modeling.

摘要

Fast screening procedures are necessary when forensic samples are being investigated, which is apparent when screening for explosives, narcotics, and bacteria. Many forensic problems can be solved by traditional analytical methods such as gas chromatography (GC) and liquid chromatography (LC). However, ion mobility spectrometry (IMS) offers several advantages that enhance its applicability as a screening procedure compared to traditional methods. Some of these advantages include its high sensitivity, low detection limits, rapid response, portability, and real-time monitoring capabilities. SIMPLe-to-use Interactive Self-modeling Mixture Analysis (SIMPLISMA) allows temporal information in the data to be exploited so that information is not lost by averaging.; Several methods were developed to produce systems that could solve forensic problems rapidly. First, by utilizing a temperature ramped thermal desorption IMS system with SIMPLISMA, interfering compounds were separated from explosives. Without the ramped thermal desorption, separation of the different compounds was not possible. Also, coupling solid phase extraction (SPE) with IMS allows for the detection of trace levels of analytes in liquid matrices. The detection of explosives in water is very important because 2,4,6-trinitrotoluene (TNT), cyclotrimethylene trinitramine (RDX), and cyclotetramethylene tetranitramine (HMX) are toxic to humans. By using SPE-IMS, detection and identification of the explosives in water was achieved, possible interferences were removed, and very low detection limits were obtained. Also, the detection of illegal narcotics and their metabolites in urine is important for workplace drug screening. The advantages of utilizing SPE-IMS for these samples include simultaneous detection of several possible compounds and removal of adulterants that might interfere with detection of the narcotics. Finally, adding a thermal hydrolysis/methylation (THM) step to IMS provides a method to detect and identify bacteria rapidly by their fatty acid methyl ester profiles. By utilizing THM-IMS, Bacillus cereus and three different Listeria bacteria could be detected and identified rapidly. SIMPLISMA and principal component analysis (PCA) were utilized to classify the data.; Solving problems in ion mobility measurements of forensic samples is possible by IMS without utilizing more complex systems such as GC-IMS or LC-IMS which reduce its applicability as a rapid screening technique.