High-resolution Electrospray Ionization/ion Mobility Spectrometer for Detection of Abiotic Amino Acids

Introduction: One of the primary goals of the current NASA thrust in Astrobiology is the detection and identification of organic molecules as part of an in-situ lander platform on the surface of Mars or Europa. The identification of these molecules should help determine whether indigenous organisms exist on the surface of Mars or in an undersea environment on Europa. In addition, a detailed organic chemical inventory of surface and near surface molecules will help elucidate the possibilities of life elsewhere in the Universe. Terrestrial life has, as its backbone, the family of molecules known as the amino acids (AA), and while AA can be found in the terrestrial environments as part of more complex molecules, such as peptides, and proteins. They also exist as individual molecules due to of the hydrolyses of biopolymers. In terrestrial biochemistry, there are 20 principal amino acids which are necessary for life. However, some forms of these molecules can be found in nature synthesized via abiotic process. For example, they are known to exist extraterrestrially as a component of carbonaceous meteorites. The idea that amino acids are readily created by abiotic means has been demonstrated by their positive identification in the Murchison CM2 meteorite, which fell in 1969. This meteorite was analyzed before contamination by terrestrial microbes could result. Three laboratories individually tested parts of the meteorite [1] and concluded that the amino acids present in them were indigenous to the meteorite because, among other reasons, they had equal Land Denantiomers. Final identification of the constituents of the Murchison included 33 amino acids which have no known biotic source, 11 amino acids which have limited distribution and 8 (Glycine, Alanine, Valine, Proline, Leucine, Isoleucine, Aspartic Acid, and Glutamic Acid) which readily occur in terrestrial proteins [2]. Ion Mobility Spectroscopy: Ion mobility spectrometry (IMS) has many features that make it attractive as an analytical separation device. IMS is simple, fast, rugged, highly selective and very sensitive to a wide range of compounds. Electrospray ionization is a soft-ionization method where molecules can be ionized at atmospheric pressures which make it a natural ionization method for ion mobility spectroscopy, which also operates at atmospheric pressures. The development of ESI/IMS greatly expanded the range of compounds to include non-volatile samples dissolved in a liquid sample that could be analyzed by IMS. The fundamentals and applications of the IMS technique are reviewed in detail elsewhere [3]. In brief, the operation of an IMS analyzer is similar to that of a time-of-flight mass spectrometer except that it can function at atmospheric pressure. When an ion is placed in a constant electric field, it migrates along the direction of the field until it collides with a neutral molecule, it then accelerates again until it suffers another collision, and so forth. The energy gained from the electric field is randomized by these collisions, and the combination of acceleration and collision over macroscopic distances results in a constant average ion velocity ( d v in the equation below) which is directly proportional to the electric field (E). In order to remove the dependence on number density, ion mobilities are reported by normalizing to standard temperature (273 K) and Pressure (760 torr). The ratio of the ion velocity to the magnitude of the electric field at standard temperature and pressure is called the reduced ion mobility (K0), which is usually specified in units of cm V s, and is given by