Stir Bar Sorptive Extraction

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Stir Bar Sorptive Extraction (of . Engl stir bar , magnetic stir bar, and sorptive extraction , sorption - extraction ), abbreviated SBSE is a method for preparing samples for subsequent analysis by gas chromatography . The method is based on the use of a sorbent- coated magnetic stir bar (trade name: Twister), which mixes the sample to be analyzed, with the analytes accumulating in the coating material. The method similar to solid phase micro-extraction was developed by Pat Sandra .

Worldwide the sole licensee for SBSE technology is Gerstel.

Structure of the twister

Structure of the twister

The Twister consists of a magnetic glass stirrer which is coated with a layer of sorbent . Polydimethylsiloxane (PDMS) and polyethylene glycol (EG) are currently used as sorbent material for the commercially available Twister , even if further materials have been announced for the future.

sampling

To take the sample, the Twister is placed in the aqueous sample, which it mixes with the aid of a magnetic stirrer and, during this, the analytes are concentrated in the PDMS layer. Since PDMS is a non-polar material , non-polar substances tend to accumulate. The absorption of substances of higher polarity can be improved by adding sodium chloride . Sampling can optionally also take place in the vapor space above the sample. Since Twisters are mechanically insensitive and easy to transport, they are often used as passive collectors . For this purpose, they are deposited in the air or in water over a longer period of time. This serves z. B. the detection of airborne pollutants.

analysis

In order to be able to analyze the enriched substances, they have to be removed from the PDMS again.

For gas chromatographic analysis , this is done by heating (thermal desorption ) of the Twister in a thermal desorption oven connected to a GC. The volatile compounds are evaporated and analyzed by subsequent GC.

Alternatively, the enriched substances can be removed from the PDMS by treatment with solvents and other analysis methods such as e.g. B. HPLC available.

Comparison with SPME

SBSE is one of the solid phase microextraction . short SPME, similar technology. In contrast to the SPME, the SBSE uses a significantly larger amount of phases. The better phase relationship leads to a two to three orders of magnitude higher sensitivity of the SBSE to SPME. The simultaneous mixing of the sample leads to a faster extraction.

However, the use of the SBSE is limited to substances that are sufficiently well enriched in PDMS. In contrast, phases of higher polarity are also available for the SPME.

SPME analytics can be easily automated. With SBSE, on the other hand, a manual intermediate step is always required between extraction and analysis, although the extraction of many samples can be carried out in parallel.

Areas of application

  • Water analysis (e.g. determination of odor sources in drinking water )
  • Environmental analysis (e.g. determination of pesticides in surface water)
  • Food analysis (e.g. determination of aromas in beer, changes in aromas in the mouth)

literature

  • Stir Bar Sorptive Extraction (SBSE), a Novel Extraction Technique for Aqueous Samples: Theory and Principles, E. Baltussen, P. Sandra, F. David, C. Cramers; J. Microcolumn Separations, 11 (10) 737-747 (1999)
  • S. Mitra, Sample preparation techniques in analytical chemistry, Wiley-IEEE, 2003