Analysis of Hydrocarbon in Common Fuels by Solid-Phase Microextraction (Spme) and Gas Chromatography-Mass Spectrometry

EXPERIMENT : 5

TITLE :

ANALYSIS OF HYDROCARBON IN COMMON FUELS BY SOLID-PHASE MICROEXTRACTION (SPME) AND GAS CHROMATOGRAPHY-MASS SPECTROMETRY

INTRODUCTION :

SPME is a technique where the sample is incubated or agitated to equilibrate the headspace. A SPME fiber is then introduced to the headspace for a predetermined period of time. The SPME fiber is then transferred to a hot GC injection port. Analytes that were adsorbed to the fiber from the sample headspace are desorbed directly in the GC inlet. SPME fibers are a distributed by Supleco and are available in a wide variety of polarities. By matching fiber polarity with target analyte characteristics, the analysis can be optimized for improved sensitivity and performance. SPME can be thought of as a very short gas chromatography column turned inside out. SPME involves the use of a fiber coated with an extracting phase, that can be a liquid (polymer) or a solid (sorbent), which extracts different kinds of analytes (including both volatile and non-volatile) from different kinds of media, that can be in liquid or gas phase. The quantity of analyte extracted by the fiber is proportional to its concentration in the sample so long as equilibrium is reached or, in case of short time pre-equilibrium, with help of convection or agitation. After extraction, the SPME fiber is transferred to the injection port of separating instruments, such as a Gas Chromatograph, where desorption of the analyte takes place and analysis is carried out.

The attraction of SPME is that the extraction is fast and simple and can be done without solvents, and detection limits can reach parts per trillion (ppt) levels for certain compounds. SPME also has great potential for field applications; on-site sampling can be done even by nonscientists without the need to have a GC-MS at each location. When properly stored, samples can be analyzed days later in the laboratory without significant loss of volatiles.

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