SBSE Development

The TDU equipment (commercially available from Gerstel GmbH, Miilheim an der Ruhr, Germany) is fully automated and connected on-line to a GC equipped with a programmable temperature vaporizer (PTV) injector for simultaneous cryotrapping of the analytes before injection. Another approach for analyte desorption is to place the stir bar in a small volume of a conventional HPLC liquid (or mobile phase) for HPLC analysis. The SBSE stir bars are trademarked as Twisters they can also be purchased from Gerstel. For more detailed information on SBSE technology, the reader is referred to two recent review articles.44 45 

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Another recently developed technique is headspace sorptive extraction (HSSE) with PDMS stir bars [552]. HSSE-GC was compared with SHS and HS-SPME. SBSE and HSSE extract organic analytes from aqueous or vapour samples. In SBSE, the stir bar is inserted into the aqueous sample and extraction takes place during stirring whereas in HSSE the glass rod is suspended within the headspace volume and sampling takes place during headspace equilibration. New trends are the development of selective sorbents. 

Stir bar sorptive extraction (SBSE) is a more recent development, and offers some advantages over SPME (Baltussen, Sandra, David and Cramers 1999 ... 

Besides classical headspace analysis, simultaneous distillation-extraction and solvent extraction, new sampling and enrichment developments include solvent-assisted flavour evaporation (SAFE) [3] and sorptive techniques like SPME solid-phase microextraction (SPME) [4,5] and stir-bar sorptive extraction (SBSE) [6], which are treated in a dedicated chapter in this book. This contribution will deal with advanced developments of GC techniques for improvement of separation and identification (classical multidimensional GC, or... 

Stir-Bar Sorptive Extraction This technique was developed to overcome the problems related to the very small amount of fiber coating material that is applied in SPME. Stir-bar sorptive extraction (SBSE) utilizes a magnetic rod coated with polymeric sorbent. Such a concept was introduced by Baltussen [92]. The magnetic stir bars have a length of 1 or 2 cm, and the polymer film a thickness of 500 or 1000 pm. The bar provides a large volume of polymer coating and its sorption capacity is much higher than in the conventional SPME method. In this technique, the sorbent-coated stir-bar is exposed directly to the liquid sample. When equilibrium is reached, the stir-bar is placed in the thermal desorber unit and analytes are released into GC. 

Headspace sorptive extraction (HSSE) is a similar technique developed by Bicchi et al. in 2000 (79). In HSSE, a PDMS stir-bar is used for head-space sampling of volatile organic molecules. This technique also has similarities to HS-SPME. There are several review articles discussing and comparing HS-SPME, DI-SPME, SBSE and HSSE (10,80-82). 

Not all of the techniques are suitable for large-scale industrial processes. SFE is clearly the most attractive technique of the ones discussed here, with more than 100 SFE productions plants and over 500 pilot plants worldwide. However, we will probably see more pilot plants based on PLE, PHWE and maybe also MASX in the future. SPME and SBSE are mostly developed for... 

SBSE is a novel sample preparation method introduced by Baltussen et al. ° based on the same mechanisms as SPME. In SBSE, a magnetic stirring bar coated with PDMS is added to water samples of 10 to 200 ml to promote the transport of analytes into the coating polymer. After a predetermined extraction period, the analytes are thermally desorbed in the GC injector or solvent extracted for HPLC analysis. The main advantage of SBSE is that 25 to 100 jA PDMS polymer is used instead of 0.5 /rl as in SPME. The applications developed with SBSE have shown low detection limits (sub-ng to ng 1 levels) and good repeatability, confirming to the great potential... 

SBSE is a novel technique recently developed by Sandra and coworkers, " which is based on the same mechanisms as SPME. 

Ref. [41] describes a procedure developed for the determination of eight organophosphoms insecticides in natural waters using SBSE combined with thermal desorption-GC-atomic emission detection (AED). Optimization of the extraction and thermal desorption conditions showed that an extraction time of 50 min and a desorption time of 6 min were sufficient. Addition of salt and adjustment of the pH were not necessary. Recoveries of seven of the compounds studied between 62 and 88%. For fenamiphos, which is highly water-soluble, recovery was only 15%. The very low detection limits, between 0.8 ng/1 (ethion) and 15.4 ng/1 (fenamiphos), indicate that the SBSE-GC-AED procedure is suitable for sensitive detection of OPPs in natural waters. 

Since only PDMS coating is available as an extraction phase, SBSE has been used predominantly for low-polarity analytes, but the problems of extraction of polar compounds may be solved by in situ derivatiziation. It is clear that further developments in stir bar coatings and designs could extend the applicability of the method. The main drawback of this method is the duration of extraction, typically 30-150 min. For this reason SBSE may be impractical for routine high-throughput laboratories. 

SBSE presents a series of advantages over the rest of extraction techniques is solvent-free (environmental friendly) could be completely automated don t requires pre-treatment of samples (reduces analytical errors) and presents greater sensitivity than SPME, reaching lower detection and quantitation limits. However, it presents two clear disadvantages compared with the other extraction techniques PDMS is the only phase commercially available to date, limiting the extraction of polar substances and a specific thermal desorption unit is required for optimize the process (Castro et al., 2008). The increase of the extraction yields for the recovery of polar compoimds could be carry out by in-site derivatization. Recently, other phases under development were referred, namely those based on the sol-gel technology, restricted access materials and molecular imprinted polymers (Prieto et al., 2010). 

Recently, a novel technique for isolation and concentration from aqueous samples, namely Stir Bar Sorptive Extraction (SBSE), was developed by E. Baltussen et al. (109). SBSE has already proven to be a very versatile technique for analytical chemistry. To illustrate the potential of SBSE for volatile analytes, this new technique in combination with thermal desorption and capillary gas chromatography coupled to a mass spectrometer was used for enrichment of lemon-flavored beverages (110). 

Moreover, quantitative analysis of volatile organic substances in aqueous matrices using isotopically labeled internal standards should also be easily achieved with high accuracy. Therefore, SBSE is expected to be the first-choice sampling technique for many flavor and fragrance applications in different matrices in future. As SBSE is still in its infancy, we are anxious to see if stir bars coated with medium polar or polar sorbents will be developed in the near future and if this new and powerful sample clean-up procedure will be extended to entirely other fields of application. 

The stir bar sorptive extraction (SBSE) is a relatively new preconcentration and solventless extraction method that was Irrst described in 1999 by Baltussen et al. [211], and further developed. SBSE is based on the same principles than the solid-phase microextraction (SPME) and relies in the partitioning of the analytes between a sample and a polymeric sorbent, followed by desorption of the analytes retained in the sorbent into an appropriate analytical system. 

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