# Application of Sorbent-Based Extraction Techniques in Food Analysis
## 5 Other SBE Approaches in Food Analysis
### Stir Bar Sorptive Extraction
Similarly to SPME strategies, for SBSE, the derivatization process can also be performed in situ on a stir bar and post-extraction with specific derivatization reactions employed: alkylation, acylation or silylation (in this case, usually post-extraction due to the sensitivity of silylation agents to water). [PERSON] et al. [149] summarized several new approaches in the analysis of polar compounds by SBSE in aqueous solutions. They involve SBSE with  
Figure 3: Theoretical recovery in the function of log K\({}_{\mathrm{ow}}\) for three sorptive extraction methods (V\({}_{\mathrm{sample}}\) = 5 mL; V\({}_{\mathrm{PDMS}}\) = 0.6 \(\mu\)L, 10.2 \(\mu\)L and 126 \(\mu\)L for SPME, Arrow-SPME and SBSE, respectively. Based on [143]. freeze concentration (called ICECLES), which is performed in a dedicated device which freezes the solution during extraction, enabling a gradual concentration of solutes in the remaining liquid part, whereas pure water freezes during the extraction process. Another proposed approach is Solvent-Swoollen PDMS (also called solvent-assisted SMSE, SA-SBSE), in which the solvent (such as dichloromethane, diethyl ether, and diisopropyl ether) acts as a modifier to PDMS, but also as an additional extraction medium. It was found to be suitable for the extraction of compounds with low K\({}_{\text{ow}}\) values, such as 2-acetyl pyrrole or indole from water, and was used for aroma compounds in wine [149]. Nowadays, the developments in the SBSE technique for food applications aim to widen the extraction efficiency for compounds of various polarities. Such an approach is reflected in the use of dual SBSE. Due to the different polarity of extracted pesticides, a dual SBSE method was proposed with simultaneous desorption of two stir bars used for extraction from different solvent systems (one of them modified with the addition of NaCl). A comprehensive review of novel approaches and sorbent technologies for SBSE was written by [PERSON] et al. [146], where examples of extraction modes for the simultaneous extraction of multiple compounds with different polarities are summarized. For such cases, apart from dual SBSE, multi-shot or sequential modes of SBSE can be used to avoid the decreased sensitivity resulting from the extraction of analytes with different polarity. Although compared to SPME, SBSE suffers from a lack of a broad range of extraction phases, developments in new phases for SBSE are also reflected in food analysis: experiments were performed with C18 coatings for sulfonamides in milk, cation exchange monoliths for cations in milk, PDMS/activated carbon for pesticides in sugarcane juice, MIPs in triazine herbicides in rice, apple, and lettuce, and TiO\({}_{2}\)-PPHF for arsenic species in chicken tissue, to name the most interesting [145]. Experiments were also performed for novel phases for SBSE such as polypyrrole, polyacrylate, or polyurethane (PU) foams. The latter were used for the analysis of pesticides in water and coffee, but also hormones and acidic pharmaceuticals [150]. Many techniques used for sorbent production are applied to SBSE coatings manufacturing at a lab scale including sol-gel technology, monolithic technology, molecularly imprinting technology and physical adhesion methods [146]. Dual-phase SBSE using two differently coated stir bars (OH-TSO-coated stir bar and C18--PDMS coated stir bar) was proposed for the extraction of preservatives of different polarity, and the sequential SBSE mode was used for the analysis of pesticides extracted under optimal conditions sequentially and desorbed in one GC-MS run. In the multi-shot mode, different sample aliquots are extracted under the same or different extraction conditions using one coated bar in each aliquot, and then the stir bars are simultaneously desorbed, whereas two stir bars are used in dual SBSE to extract two aliquots of a sample under different extraction conditions before both stir bars are simultaneously desorbed for the subsequent analysis.