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• To be able to identify the instrumental requirements for hydride-generation atomic absorption spectroscopy (HyFAAS).
• To be able to identify the instrumental requirements for flame photometry (FP).
• To be able to identify the instrumental requirements for inductively coupled plasma-atomic emission spectroscopy (ICP-AES).
• To be able to identify the instrumental requirements for inductively coupled plasma-mass spectrometry (ICP-MS).
• To understand the relevance of anodic stripping voltammetry (ASV) in trace metal analysis.
Methods for Environmental Trace Analysis
• To understand the relevance of X-ray fluorescence spectroscopy for the analysis of metals in solid samples.
• To understand the relevance of ion chromatography for the analysis of anions in solution.
After sample preparation comes the analysis. Depending on whether you are looking for organic or inorganic pollutants will determine the choice of analytical technique.
Suggest the appropriate analytical technique(s), from the list below, for the analysis of the following organic and inorganic pollutants.
Polycyclic aromatic hydrocarbons (PAHs)
Total petroleum hydrocarbons (TPHs)
• gas chromatography with flame ionization detection (GC-FID)
• gas chromatography with electron-capture detection (GC-ECD)
• gas chromatography with mass-selective detection (GC-MSD)
• high performance liquid chromatography with ultraviolet/visible detection (HPLC-UV/vis)
• high performance liquid chromatography with fluorescence detection (HPLC-FL)
• Fourier-transform infrared (FTIR) spectroscopy
• flame atomic absorption spectroscopy (FAAS)
• graphite-furnace atomic absorption spectroscopy (GFAAS)
• hydride-generation atomic absorption spectroscopy (HyFAAS)
• flame photometry (FP)
Instrumental Techniques for Trace Analysis
• inductively coupled plasma-atomic emission spectroscopy (ICP-AES)
• inductively coupled plasma-mass spectrometry (ICP-MS)
• X-ray fluorescence (XRF) spectroscopy
• anodic stripping voltammetry (ASV)
• ion chromatography (IC) with conductivity detection
11.2 Environmental Organic Analysis
11.2.1 Chromatographic Techniques
Environmental organic compounds can be analysed by a variety of techniques, including chromatographic and spectroscopic methods. However, in this present section the main focus will be on the use of chromatographic approaches. It is also not the intention here to give a complete and detailed study of chromatographic analysis but to provide a general overview of the types of separation frequently used in environmental organic analysis. The two most common approaches for separation of an analyte from other compounds in the sample extract are gas chromatography (GC) and high performance liquid chromatography (HPLC).
What is the essential difference between GC and HPLC?
The essential difference between the two techniques is the nature of the partitioning process. In GC, the analyte is partitioned between a stationary phase and a gaseous phase, whereas in HPLC the partitioning process occurs between a stationary phase and a liquid phase. Separation is therefore achieved in both cases by the affinity of the analyte of interest with the stationary phase. The higher the affinity, then the more the analyte is retained by the column.
The choice of which technique is employed is largely dependent upon the analyte of interest. For example, if the analyte is thermally labile, does not volatilize at temperatures up to 250°C and is strongly polar, then GC is not the appropriate technique. However, HPLC can then be used (and vice versa).
188.8.131.52 Gas Chromatography
Separation in GC is based on the vapour pressures of volatilized compounds and their affinities for the liquid stationary phase, which coats a solid support, as they pass down the column in a carrier gas. The practice of GC can be divided into two broad categories, i.e. packed- and capillary-column based. For
Methods for Environmental Trace Analysis
the purpose of this discussion, only capillary-column GC will be discussed. A gas chromatograph (Figure 11.1) consists of a column, typically 15-30 m long, with an internal diameter of 0.1-0.3 mm. The range of column types available from manufacturers is considerable; however, some common types are frequently encountered e.g. the DB-5 type (Figure 11.2).
Why do you think that this column is known as a DB-5?
The DB-5 is a low-polarity column in which the stationary phase, consisting of 5% phenyl- and 95% methylsilicones, is chemically bonded onto silica. In a similar manner, a DB-1 column consists of 100% methylsilicone.
Figure 11.1 Schematic diagram of a typical gas chromatograph. Reproduced by permission of Mr E. Ludkin, Northumbria University, Newcastle, UK.