Organic Geochemistry

Introduction

GC-MS is an instrumental technique by which complex mixtures of volatile, dominantly organic compounds are separated, identified and, if needed, quantified. In order to be analyzed by GC-MS, compounds must be sufficiently volatile and thermally stable. MS detection enables the determination of molecular masses of target compounds and the elucidation of their molecular structure. The latter can be deduced from the specific fragmentation patterns that organic compounds show upon bombardment with fast electrons in an MS ion source. This mode is called electron ionization (EI) under which sample molecules lose an electron resulting in a molecular ion (M+., radical cation). Due to the high amount of energy (70 eV) impacted to the molecular ion it usually fragments producing further smaller ("daughter") ions with characteristic relative abundances that provide a "fingerprint" for that molecular structure. Using searchable data bases, this information helps to identify compounds of interest and supports structural elucidation of unknown components.

In the Hinrichs Lab three regular GC-MS couplings exist (see below). Two of the three GC-MS systems are additionally equipped with FIDs so that the GC effluents can be split to both detectors, the MS and the FID. This offers the simultaneous determination of concentration and molecular structure in one analytical run.