Neural Network Prediction of Reduced Ion Mobility of Amino Acid Based on Molecular Structure

Introduction: Ion Mobility Spectrometer (IMS) is a useful approach for trace analytes detection in gas phase sample matrices and it is a real time, light weight and no pumping required system which has been developed as a small, portable and stand alone device[1-5] for a low cost, accuracy and high speed approach. Moreover, IMS is also a friendly operation device whether it stands alone or combining with the gas chromatography to make it more attractable system feature. Several portable IMS systems have developed for the detection of chemical warfare agents and other toxic entities. Moreover, the portable IMS devices are also useful in other applications e.g., drugs, explosives, and pollutants [6-8]. The details of the IMS system can be found in our earlier publications[9]. In brief, IMS is a high-pressure time-of-flight (TOF) method based on elastic collisions of an ion with a buffer gas. It is advantageous over the other detection methods because it can operate at the same pressure as the ESI resulting in no differential pumping when the ions go from ionizer to analyzer. The mobility itself is related to the size and shape of the ion imparting a second dimension of se-lectivity which enables IMS to separate isomers such as leucine and isoleucine[10]. IMS has been demonstrated to be very sensitive in detecting organic compounds and is currently the instrument of choice for field detection of explosives and chemical/biological warfare agents[11]. In NASA perspective, one of the primary objectives in the burgeoning field of astrobiology is the in situ detection and identification of organic molecules on the surface of Mars, Europa, and elsewhere where amino acids are believed to be vital to the basic functions of terrestrial biology [9]. A detailed inventory of organic molecules present on extraterrestrial bodies will certainly broaden our general understanding of the solar system and may help elucidate questions regarding the origin of life on Earth and the possibility of life elsewhere in the Universe. These intriguing possibilities have prompted a flurry of activity in terms of investigating various means of performing such detection and identification. As such, this work is intended to further examine the feasibility of high resolution electrospray ionization ion mobility spectrometry (ESI-IMS) as a tool for in situ analysis of organic compounds [9,12].