Chlorophenols in soils and sediments: Sensitive triple-step procedure saves time

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  • Published: Jun 11, 2012
  • Author: Steve Down
  • Channels: Sample Preparation
thumbnail image: Chlorophenols in soils and sediments: Sensitive triple-step procedure saves time

Chlorophenol contaminants

A combination of microwave-assisted extraction and dispersive liquid-liquid extraction with minimal use of organic solvent has been applied to the removal of chlorophenols from sediments and soils.

Chlorophenols are common contaminants which the general public might be aware of due to their occurrence in drinking water. They are produced as by-products during the disinfection of water by chlorine and have a sharp, medicinal taste with a low threshold that makes them easy to notice. They are also manufactured for use as pesticides and antiseptics and are produced during the bleaching of wood pulp to make paper.

At low levels, chlorophenols are generally safe but they can cause damage to the immune system and to the liver at high doses which might be encountered in industrial incidents. They are also suspected estrogens. So, it is important that water and environmental matter is regularly tested for the presence of this group of chlorinated compounds.

A number of analytical methods already exist for environmental chlorophenols, with HPLC being popular. Now, a team of Iranian scientists has developed a new extraction procedure for soils and sediments prior to HPLC which they claim is superior to published methods because it reduces the amount of organic solvent and incorporates two micro steps.

Yadollah Yamini, Mohammad Hosein Naeeni, Mohammad Rezaee and Shahram Seidi from Tarbiat Modares University, Tehran, described their process in the Journal of Separation Science.

Microwaves and microextraction

The method was designed specifically for five chlorophenols which were added to soil in known amounts in order to facilitate optimisation. They were 2- and 4-chlorophenol, 2,3- and 2,5-dichlorophenol and 2,4,6-trichlorophenol.

In the first step, small samples (1.2 g) were mixed with alkaline water at pH 10. The mixture was subjected to microwave irradiation for 90 seconds and allowed to cool. The adoption of water rather than an organic solvent makes it a cleaner, more environmentally benign process.

The supernatant from the resultant solution was then mixed with a small volume of acetone as dispersant and chlorobenzene as extractant for dispersive liquid-liquid microextraction. Chlorobenzene was the most efficient of a series of chlorinated solvents and undecanol that were tested and acetone was a better dispersant than acetonitrile and methanol.

The chlorobenzene droplets containing the chlorophenols were collected at the bottom of the tube by centrifugation then submitted to the third and final step of the extraction process, a back extraction with alkaline water. This took place in a microsyringe in which the plunger was repeatedly drawn in and out to increase contact between the two phases.

The final aqueous solution was injected into the HPLC system for separation of the extracted chlorophenols on an octadecyl silica column with a gradient of acetonitrile in acidic phosphate buffer and UV-vis detection at 210 nm.

Triple play for faster extraction

The detection limits for the five chlorophenols are 0.5-2.0 µg/kg soil or sediment, which are better than those of six reported methods. So, lower detection limits are achieved in shorter times. The enrichment factors are 23-29 and recoveries are in the range 66-82% with no clean up of the samples required before or after the microwave-assisted extraction step.

Soil from a farm field, sediment from the southern Iranian coastline and sediment from the north of the country were used to test the method. No chlorophenols were detected in any of them, so known amounts were added to check for any matrix effects.

All of the chlorophenols were slightly under-quantified with recoveries of 80.7-97.5% and the relative standard deviations were acceptable at less than 9.7%, so the method was deemed to be satisfactory.

Although three steps are involved, they are all carried out quickly. The method takes just 6 minutes for extraction, compared with 9-12 minutes for other microwave extraction-based procedures but uses only 1 mL of solvent in total. It provides a simple alternative for the extraction of chlorophenols from soil and sediments.

Related Links

Journal of Separation Science 2012 (Article in Press): "Microwave-assisted extraction combined with dispersive liquid–liquid microextraction as a new approach to determination of chlorophenols in soil and sediments"

Article by Steve Down

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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