The present State of GC-MS

The Current State of GC-MS



The Current State of GC-MS

Introduction

Gas chromatography mass spectrometry is an instrumental method, encompassing a gas chromatograph (GC) coupled to a mass spectrometer (MS), by which complex mixtures of chemicals may be separated, identified and quantified. Current state makes it ideal for the analysis of the hundreds of relatively low molecular weight compounds found in environmental materials. In order for a compound to be analysed by GC/MS it must be sufficiently volatile and thermally stable (Hamilton, 76). In addition, current state functionalised compounds may necessitate chemical alteration (dramatization), prior to analysis, to eliminate undesirable adsorption effects that would otherwise affect the quality of the data obtained. Samples are generally investigated as organic solutions consequently components of interest (e.g. soils, sediments, tissues etc.) need to be solvent extracted and the extract subjected to various 'wet chemical' techniques before GC/MS analysis is possible (Clement, 528).

The experiment answer is injected into the GC inlet where it is vaporized and cleared up on a chromatographic column by the carrier gas (usually helium). The experiment flows through the pillar and the compounds comprising the mixture of interest are divided by virtue of their relation interaction with the outer layer of the column (stationary phase) and the carrier gas (mobile phase). The last mentioned part of the pillar passes through a heated move line and finishes at the entry to ion source (Fig. 1) where mixtures eluting from the pillar are converted to ions.

Two promise procedures live for ion production. The most often utilised procedure is electron ionisation (EI) and the rarely utilised alternate is chemical ionisation (CI). For EI a beam of electrons ionise the experiment molecules producing in the decrease of one electron. A molecule with one electron missing is called the molecular ion and is represented by M+ (a radical cation). When the resulting peak from this ion is seen in a mass spectrum, it gives the molecular weight of the compound (Watson, 846). Due to the large allowance of power imparted to the molecular ion it generally fragments making farther lesser ions with attribute relation abundances that provide a 'fingerprint' for that molecular structure. This information may be then used to identify compounds of interest and help elucidate the structure of unknown components of mixtures (Kintz, 62). CI starts with the ionisation of methane (or another suitable gas), conceiving a radical which in turn will ionise the experiment molecule to make [M+H] + molecular ions. CI is a less energetic way of ionising a molecule hence less fragmentation occurs with CI than with EI, hence CI yields less data about the detailed structure of the molecule, but does yield the molecular ion; occasionally the molecular ion cannot be noticed utilising EI, hence the two methods support one another. Once ionised a small positive is used to repel the ions out of the ionisation chamber (Baek, 298).

The next constituent is a mass analyser (filter), which separates the positively ascribed ions according to diverse mass related ...