Organic contaminants trace levels

On-line LC-GC has frequently been used as a clean-up technique for the analysis of trace levels of contaminants (pesticides, plasticizers, dyestuffs and toxic organic chemicals) in water and food products. Several different approaches have been proposed for the analysis of contaminants by on-line LC-GC. Since pesticide residues occur at low concentration in water, soil or food, extraction and concentration is needed before GC analysis is carried out. 

A wide range of analytical techniques have been developed in order to identify the organic contaminants often present at trace levels in complex environmental samples such as wastewaters. These techniques mainly use gas chromatography (GC) and liquid chromatography (LC). 

Membrane treatment is a very effective technology used in a broad range of applications. It has been used for desalinization, specific ion removal, nutrients and suspended solids removal, and nowadays plays an important role in removal of trace-level organic contaminants dissolved in water. It is a very advantageous... 

Concentration Plus Solvent Transfer. Concentration of the organic solutes is essential to the determination of many organic contaminants present in water at very trace levels. The solvent transfer is needed for implementation of the separation and detection schemes that do not tolerate the water matrix. For bioassay work, concentration and solvent transfer are also needed because the amounts are too low for direct testing of the water solutions, and dimethyl sulfoxide. (DMSO) is the preferred solvent. In bioassay studies that involve animal exposure, the concentration scheme must accommodate very large volumes of water. Theoretically and practically, these elements of the analytical and bioassay methodologies can be achieved by using solid adsorbents, especially synthetic polymers. 

Tomson MB, Dauchy J, Hutchins S, et al. 1981. Groundwater contamination by trace level organics from a rapid infiltration site. Water Research 15 1109-1116. 

Thousands of pollutants contaminate our environment, including organic, inorganic, and biological species. It has been reported that, generally, contaminants are found in the environment at trace levels [188,189]. Of course, conventional analytical methods have been used for their monitoring but these methods cannot detect contaminants present at extremely low concentrations. This challenge was overcome by newly developed microfluidic devices such as NCE. 

Several existing protocols require a solvent (acetone, methanol, isopropanol) rinse as part of equipment decontamination for VOC sampling and 1 10 percent hydrochloric or nitric acid rinse for metal analysis sampling (DOE, 1996 USACE, 1994). These practices, successful as they may be in removing trace level contaminants, create more problems than they are worth. Organic solvents are absorbed by the polymer materials used in sampling equipment construction and appear as interferences in the VOC analysis. Acid destroys the metal surfaces of soil sampling equipment and induces corrosion. The use of solvents and acids is a safety issue and it also creates additional waste streams for disposal. 

In the analysis of metals in petroleum and petroleum products one of the most common sample preparation procedures is the dilution of the sample with an organic solvent such as xylene, methyl isobutyl ketone (MIBK) or white spirit. It is of great importance that the solvent system chosen is as free as possible from metallic contamination. Elements such as sodium and zinc are commonly found in many organic solvents. Similarly, other reagents such as mineral acids must be investigated for metal content before use. Where ultra-trace level determinations are to be attempted the reagents used may need to be purified. For solvents, the use of redistillation or extraction with mineral acid may improve the blank levels. 

This chapter has identified the main extraction techniques used for the extraction of organic analytes from solid matrices, e.g. soil. The main purpose of each technique has been to remove the analyte from the matrix as effectively as possible. In some instances, e.g. supercritical fluid extraction, some attempt is made to achieve selectivity of extraction by altering the operating conditions, such as temperature and pressure, or by the addition of an organic modifier. In other situations, the sole purpose of the extraction technique is to remove the analyte from the matrix under the strongest possible conditions without any concern for selectivity. The selectivity in these circumstances results exclusively from the method of analysis which follows. It should also be borne in mind, depending on the level of contamination of the sample, that further extract pre-concentration and/or clean-up may be required prior to analysis in order to achieve trace level analytical results. The methods used for effective pre-concentration are described later in Chapter 10. 

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