Chromatography is the method of separation in which several chemicals to be separated for subsequent analyses are distributed between two phases. In GC, separation is based mainly on the partitioning between a gas mobile phase and a liquid stationary phase. It is estimated that more than 60 types of GC detectors have been developed. For analysis of samples from the environment the few most commonly used are flame ionization detector (FID), thermal conductivity detector (TCD), electron capture detector (ECD), nitrogen-phosphorous detector (NPD), flame photometric detector (FPD), photo ionization detectors (PID) and mass selective detector or mass spectrometer (MS) which also allows qualitative and quantitative analysis (Driscoll, 2004). The GC-FID technique is a routine technique for the quantitative analysis of all the non-polar hydrocarbons which are extracted by applied solvents (n-hexane or acetone / n-heptane), and it has various scopes, depending on the standard (ISO 16703, 2004; Jovančićevič et al., 1997; Jovančićević et al., 2007). It is also used for rapid semiquantitative assessments of the successfulness of bioremediation treatments of polluted environments (water, soil, sediments) or the decomposition of hydrocarbon materials originating from oil under natural conditions or historical pollution (Beškoski et al. 2011; Hinchee and Kitte, 1995; Jensen et al., 2000; Jovančićević et al., 2008; Milic et al., 2009). GC methods are sensitive, selective and can be used to determine the specific target compounds. In environmental science GC methods are mainly used for: identifying organic pollutants in recent sediments, following abiotic and biotic transformations of petroleumtype pollutants, improving our understanding of migration mechanisms of organic Pollutants in soil/water/air environments, distinguishing the oil pollutant from the native organic substance of recent sediments, fingerprinting and differentiation of petroleum-type pollutants, following transformation of petroleum pollutant during soil bioremediation experiments, determining other organic pollutants such us POP’s (persistent organic pollutants) and analysing petroleum biomarkers.
Gas chromatography coupled with mass spectrometry
GC-MS is routinely applied to identify the individual components of petroleum hydrocarbons. These methods have high selectivity and compounds can be authenticated by Gas Chromatography – Biochemicals, Narcotics 6 and Essential Oils analysing retention times and unique mass spectra. GC-MS can confirm the presence of the target analyte and the identification of untargeted analyte and also can be used for the separation of hydrocarbons into the groups. The main drawback of these methods is that isomeric compounds can have identical, and many different compounds can have similar mass spectra. Heavy fuel oil can contain thousands of components that cannot be separated in the gas chromatograph. Different compounds may have the same ions, which complicates the identification process (Jensen et al, 2000). Determination of TPH is possible using different methods - gravimetrically (DIN EN 14345, 2004), by infrared spectroscopy (ISO/TR 11046, 1994) or GC (ISO 16703, 2004). All these methods can be used for the quantitative analysis of analytes; however, when it comes to a mixture of compounds which is often the case with environmental samples, qualitative analysis can be realized only by GC-MS.
Novel GC techniques
The common techniques listed above, have now been in use for several decades but new techniques offer greater opportunities in this area. GC coupled to high-resolution time-offlight mass spectrometry (GC–TOF–MS) has been applied for non-target screening of organic contaminants in environmental samples (Serrano et al., 2011). GC–TOF–MS has been successfully applied for screening, identification and elucidation of organic pollutants in environmental water and biological samples (Hernández et al., 2011) and also for confirmation of pollutants in a highly complex matrix like wastewater (Ellis et al., 2007). The strong potential of GC–TOF–MS for qualitative purposes comes from the full spectrum acquisition of accurate mass, with satisfactory sensitivity. Comprehensive two-dimensional GC (GC×GC) coupled with MS has been widely applied in environmental analyses in the last decade (Ieda et al., 2011). The GC×GC–MS method has
many practical advantages, e.g. high selectivity, high sensitivity, large separation power, group type separation and total profiling. Panić and Górecki reviewed GC×GC in environmental analyses and monitoring and they indicated that the main challenge in environmental analysis is that the analytes are usually present in trace amounts in very complex matrices (Panić & Górecki, 2006). In overcoming this problem, GC×GC–MS is a
very powerful and attractive system that has been successfully applied for powerful identification of polychlorinated dibenzodioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) (de Vos et al., 2011), polychlorinated biphenyls (PCBs) (Focant et al., 2004; Hoh et
al., 2007), polychlorinated naphthalenes (PCNs) (Korytár et al., 2005), nonyl phenol (NP) (Eganhouse, et al., 2009), benzothiazoles, benzotriazoles, benzosulfonamides (Jover et al.,
2009), Cl-/Br-PAH congeners (Ieda et al., 2011), pharmaceuticals and pesticides (Matamoros et al., 2010) in complex environmental samples.