ASTROBIOLOGY Volume 8, Number 2, 2008 © Mary Ann Liebert, Inc. DOI: 10.1089/ast.2007.0176 Research Paper Analysis of Underivatized Amino Acids in Geological Samples Using Ion-Pairing Liquid Chromatography and Electrospray Tandem Mass Spectrometry DE-LING LIU,* LUTHER W. BEEGLE, and ISIK KANIK ABSTRACT The capability of detecting biomarkers, such as amino acids, in chemically complex field sam- ples is essential to establishing the knowledge required to search for chemical signatures of life in future planetary explorations. However, due to the complexities of in situ investiga- tions, it is important to establish a new analytical scheme that utilizes a minimal amount of sample preparation. This paper reports the feasibility of a novel and sensitive technique, which has been established to quantitate amino acids in terrestrial crust samples directly without derivatization using volatile ion-pairing liquid chromatography and tandem mass spectrometry equipped with an electrospray ionization source. Adequate separation of 20 un- derivatized amino acids was achieved on a C 18 capillary column within 26 min with nona- fluoropentanoic acid (NFPA) as ion-pairing reagent. Each amino acid was identified from its retention time as well as from its characteristic parent-to-daughter ion transition. Using tan- dem mass spectrometry as a detection technique allows co-elution of some amino acids, as it is more specific than traditional spectrophotometric methods. In the present study, terrestrial samples collected from 3 different locations were analyzed for their water-extractable free amino acid contents, following the removal of metal and organic interferences via ion ex- change procedures. This is the first time that amino acids in geological samples were directly determined quantitatively without complicated derivatization steps. Depending on the amino acid, the detection limits varied from 0.02 to 5.7 pmol with the use of a 1 l sample injection loop. Key Words: Mars—In situ life detection—Organic molecules—Amino acids. Astrobiol- ogy 8, 229–241. 229 INTRODUCTION T HE IMPORTANCE OF AMINO ACIDS is well estab- lished in terms of their roles as fundamental building blocks in biological processes; thus the presence of amino acids in various geological en- vironments can be indicative of the existence of extant life. The capability of detecting biomark- ers, such as amino acids, in chemically complex terrestrial samples is essential to establishing the knowledge required to search for evidence of life in future planetary explorations. As far as ex- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California. *Present address: The Aerospace Corporation, El Segundo, California.