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Table 7.3 Current USEPA methods for the extraction of organic pollutants from solid environmental samples
3540 Soxhlet extraction
3541 Automated Soxhlet
3545 Accelerated solvent
extraction (pressurized fluid extraction)
3550 Ultrasonic extraction
3560 Supercritical fluid extraction
3561 Supercritical fluid
3562 Supercritical fluid
Semi-volatile and non-volatile organics from soils, relatively dry sludges and solid wastes Polychlorinated biphenyls, organochlorine pesticides and semi-volatiles from soils, relatively dry sludges and solid wastes Semi-volatiles and non-volatile organics from soils, relatively dry sludges and solid wastes Semi-volatiles and non-volatile organics from soils, relatively dry sludges and solid wastes
Semi-volatile petroleum hydrocarbons from soils, relatively dry sludges and solid wastes
Polycyclic (polynuclear) aromatic
hydrocarbons from soils, relatively dry sludges and solid wastes Polychlorinated biphenyls and
organochlorine pesticides from soils, sediments, fly ash, solid-phase extraction media, and other solid materials which are amenable to extraction with
Considered a rugged extraction method because it has very few variables that can adversely affect extraction recovery Allows equivalent extraction efficiency to Soxhlet extraction in 2 h
Extraction under pressure using small volumes of organic solvent
Considered to be less efficient than the other methods detailed; rapid method that uses relatively large solvent volumes. Not appropriate for use with organophosphorus compounds as it may cause destruction of the target analytes during extraction Normally uses pressurized C02 with additional small volumes of organic solvent. Limited applicability. Relatively rapid extractions As method 3560
As method 3560
Methods for Environmental Trace Analysis
1. Saim, N.,Dean, J. R., Abdullah, Md. P. andZakaria, Z., J. Chromatogr., A, 791, 361-366 (1997).
2. Hancock, P. and Dean, J. R., Anal. Commun., 34, 377-379 (1997).
3. de la Tour, C., Ann. Chim. Phys., 21, 127-132, 178-182 (1822).
4. Dean, J. R., Barnabas, I. J. and Owen, S. P., Analyst, 121, 465-468 (1996).
5. Richter, B. E., Jones, B. A., Ezzell, J. L., Porter, N. L., Avdalovic, N. and Pohl, C., Anal. Chem., 68, 1033-1039 (1996).
6. Fitzpatrick, L. J., Dean, J. R., Comber, M. H. I., Harradine, K., Evans, K. P. and Pearson, S., J. Chromatogr., A, 874, 257-264 (2000).
7. Heslop, C. A., ‘Identification and extraction of alcohol ethoxylated non-ionic surfactants in environmental samples’, PhD Thesis, Northumbria University, Newcastle, UK, 2000.
Methods for Environmental Trace Analysis. John R. Dean
Copyright © 2003 John Wiley & Sons, Ltd.
ISBNs: 0-470-84421-3 (HB); 0-470-84422-1 (PB)
• To understand the need for separation and/or pre-concentration for organic compounds in solution.
• To understand the theory of liquid-liquid extraction.
• To be able to carry out solvent extraction in a safe and controlled manner.
• To understand the requirements for solid-phase extraction (SPE).
• To be able to carry out SPE in a safe and controlled manner.
• To understand the theory of solid-phase microextraction (SPME).
• To understand the requirements for SPME.
• To be able to carry out SPME in a safe and controlled manner.
8.1 Liquid-Liquid Extraction
The principal of liquid-liquid extraction (LLE) is that the sample is distributed or partitioned between two immiscible solvents in which the analyte and matrix have different solubilities. The main advantage of this approach is the wide availability of pure solvents and the use of low-cost apparatus. For the background theory on LLE, see Box 6.1 earlier.
Can you think of any circumstances when liquid-liquid extraction would be useful?
Liquid-liquid extraction is required when the analyte is present at a low concentration in a water sample, e.g. river water. In this case, LLE is
Methods for Environmental Trace Analysis
used to pre-concentrate the analyte from a large volume of water into a small sample volume. In addition, or at the same time, LLE can be used to clean-up the analyte from its matrix. Liquid-liquid extraction is therefore a very useful technique in trace analysis.
8.2 Solvent Extraction
Two common approaches are possible here. In the first approach, the extraction is carried out discontinuously where equilibrium is established between two immiscible phases, or secondly by continuous extraction. In the case of the latter, equilibrium may not be reached. The selectivity and efficiency of the extraction process is critically governed by the choice of the two immiscible solvents. Using aqueous and organic (e.g. dichloromethane, chloroform, ethylene acetate, toluene, etc.) pairs of solvents, the more hydrophobic analytes prefer the organic solvent while the more hydrophilic compounds prefer the aqueous phase. The more desirable approach is quite often reflected in the nature of the target analyte. For example, if the method of separation to be used is reversed-phase high performance liquid chromatography (HPLC), then the target analyte is best isolated in the aqueous phase. In this situation, the target analyte can then be injected directly into the HPLC system. [Note - the target analyte may well require additional pre-concentration, e.g. solid-phase extraction or solvent elimination (see later), to achieve the appropriate level of sensitivity.] In contrast, if the target analyte is to be analysed by gas chromatography, it is best isolated in organic solvent. In addition, isolation of the target analyte in the organic phase allows solvent evaporation to be employed (see Chapter 10), thus allowing concentration of the target analyte.