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Sample size 1-2 l 1-1000 ml 1-1000 ml
Extraction Discontinuous, 10-20 min 10-60 min (requires
time 20 min; continuous, up to 24 h optimization)
Solvent con- 30-60 ml for Organic solvent No solvent required
sumption discontinuous; required for
(ml) per up to 500 ml for wetting sorbent
extraction continuous and elution of analyte (10-20 ml)
Equipment Low Low-high (depends Low (but also
cost on degree of automation) available as an automated system)
Acceptability Wide acceptance for isolating organic compounds Widely acceptable Gaining in popularity; new technology
EPA method 3510 and 3520 3535 None
Methods for Environmental Trace Analysis
Chapter 11 Response 11.1
To answer this question requires knowledge of what the actual analytical techniques measure, plus knowledge of what the pollutants are. If you are unsure about what each analytical technique measures, then complete this chapter before attempting to answer this question. Knowledge of the pollutants may have been gained while working through the book to this stage. If not, you should consult the ‘Resources’ section towards the end of this book (see Section 12.2).
Attempts to determine the appropriate analytical technique for each pollutant can be carried out at three different knowledge levels. At the first level, the ‘novice’ level, it should be easy to establish whether the pollutant can be determined by using an analytical technique capable of determining organic or inorganic pollutants. However, with a greater understanding of the analytical techniques, and what they are capable of, comes additional questions, e.g. at what concentration level is the pollutant likely to be present? Is the pollutant in an aqueous solution or in solid form? This additional level of knowledge, or ‘intermediate’ level, comes with experience and a more advanced study of the various techniques. I would define the ‘advanced’ level as appropriate for someone with both theoretical and detailed practical knowledge of the techniques.
The completed table below indicates the level of knowledge expected for someone who has some basic understanding of the various analytical techniques (the ‘novice’ level).
Polycyclic aromatic hydrocarbons (PAHs) GC or HPLC
Lead FAAS/ICP - AES/ICP- MS
Phenols GC or HPLC
Chlorinated pesticides GC
Benzene - toluene - ethylbenzene- xylene(s) GC
Total petroleum hydrocarbons (TPHs) GC
However, for students with an additional level of knowledge ‘intermediate’ level, the choice of analytical technique has some additional complexities (as discussed below).
Polycyclic aromatic hydrocarbons (PAHs). These can be routinely determined by using GC with FID or MSD. For trace level analysis, the use of MSD is preferred
Responses to Self-Assessment Questions
as it allows the mass spectrometer to be used in the selected-ion monitoring (SIM) mode, which has the additional benefit of providing target analysis of the selected PAHs via their ions (mass/charge ratio). However, it is also possible to determine PAHs with UV/Vis or fluorescence detection. As all of the PAHs are aromatic (i.e. possess a chromophore), they can be detected in both of these ways. The latter detection method offers additional sensitivity when compared to UV/vis detection.
Lead. This inorganic pollutant can be determined by a whole range of analytical techniques; in addition, information is often required on the concentration level of lead. In terms of sensitivity (least sensitive first), the following is suggested: FAAS < ICP-AES < GFAAS = ASV < ICP-MS. While all of these techniques can determine lead in solution, the use of XRF allows lead to be determined directly in the solid.
Phenols. These can be determined by both GC and HPLC. In this situation, the choice of technique will be dependent upon other factors, such as the choice of separation column. In some cases, phenols can only be analysed by GC after prior derivatization of the phenols into more volatile species. The preferred method is therefore suggested to be HPLC with UV/Vis detection.
Chlorinated pesticides. These can be determined by GC. The specific description of the pollutants as chlorinated pesticides should immediately indicate that the choice of detection should be ECD. While this method will provide specific and sensitive detection of chlorinated pesticides, the optional benefits of MSD (see PAHs) may be advantageous.
Arsenic. This is a volatile metalloid capable of forming an hydride. The immediate choice, therefore, would be HyFAAS. This would provide a sensitive method of determining arsenic. In addition, the use of inductively coupled plasma techniques is also a possibility. It would not be unreasonable for maximum sensitivity to couple the hydride generation apparatus up to the ICP-MS system. However, the use of the latter has one area of concern with respect to arsenic determination. As arsenic is monoisotopic (only one isotope, at 75 amu), interferences can result in the presence of chlorine-forming species e.g. HCl. If this is the case, the use of chlorine-containing material should be avoided. Alternatively, remove the potential interference from chlorine-containing material by performing some chromatographic separation prior to the ICP-MS stage.