# Application of Sorbent-Based Extraction Techniques in Food Analysis
## 5 Other SBE Approaches in Food Analysis
### Stir Bar Sorptive Extraction  
SBSE was developed in 1999 based on the observation of absorption/adsorption phenomena on PDMS, introduced as magnetic stir bars coated with PDMS and almost instantly commercialized as Twister by Gerstel [141]. Since the development of the technique, it has gained high popularity in various aspects of environmental, pharmaceutical, biomedical and food and flavor extractions. Many reviews summarized the developments in SBSE, with the first 10-year period thoroughly described by [PERSON] et al. [142] and the developments of recent decades described by [PERSON] et al. [143]. The sensitivity obtained by SBSE, which made it the preferred technique for many trace analyses, is related to the volume of PDMS compared to other techniques in which PDMS is used as an absorbent (i.e., SPME), though the desorption of analyte from such a high-volume (and thick layer) sorbent also poses problems for carry over and incomplete desorption of compounds absorbed into PDMS (memory effect) [144]. The benefits of SBSE compared to other techniques are presented in Figure 3, which shows the comparison of theoretical recoveries of analytes as a function of the octanol/water partition coefficient (log K\({}_{\text{ow}}\)). It is evident that, especially for compounds with lower log K\({}_{\text{ow}}\), SBSE is superior to SPME or Arrow-SPME (which operates similarly to SPME but has more sorbent) in terms of extraction yield. Figure 2: Different geometries of SPME. The idea behind SBSE makes it ideal for trace analysis; therefore, it found numerous applications in food analysis [145]. SBSE in the direct extraction mode is used for the extraction of analytes from liquid foods; for solid foods, ultrasonic extraction is sometimes used. In food analysis, SBSE is used in fields where high sensitivity is required, i.e., for trace analysis of contaminants such as pesticides, PAHs, phenols furans, volatiles and compounds responsible for off-odors. PDMS-coated stir bar extraction is similar to LLE using a polar solvent; therefore, this approach is used for the extraction of contaminants from non-fatty matrices, such as juice, wine, fruit and vegetables [146]. The main disadvantage of SBSE in food analysis was the lack of various extraction phases, with a polar PDMS used in the majority of cases. In food analysis, the extraction of polar compounds at trace levels is a challenging task. The difficulties in the extraction of polar compounds from food matrix often result in their under-representation when, for example, aroma compounds are profiled in foods [2]. The situation in SPME is better due to the higher number of fiber coatings of different polarity available; however, SBSE offers higher compound capacity due to its much higher phase volume than SPME. SBSE phases for polar compounds have been developed; however, their robustness and stability are low and they were used mostly with liquid, not with thermal desorption. The most popular alternative coating is polyethylene glycolmodified silicone (EG). This can be used with thermal desorption, though its durability is still lower compared to PDMS. SBSE with EG was used for the extraction of volatile phenols from alcoholic beverages as the limited affinity of PDMS to polar compounds makes their extraction (especially for 4-vinylphenol) unsatisfactory. Low LOQs (<3 \(\mu\)g/L) make it an attractive method considering the influence of these compounds on the aroma of alcoholic beverages [147]. An alternative approach for the analysis of polar compounds (K < 3.0) in aqueous samples is their derivatization, which aims at lowering the polarity of analyzed compounds and increasing the recoveries of the derivatives. Such an approach is usually performed for target analysis of thiols or carbonyl compounds in alcoholic beverages [148].