# Application of Sorbent-Based Extraction Techniques in Food Analysis
## 5 Other SBE Approaches in Food Analysis
### Molecularly Imprinted Polymers (MIPs)  
For sorbent-based methods, the lack of selectivity of sorbents is the main drawback. In research on selective sorbents, different materials have been tested, such as restricted-access materials (RAMs), immunosorbents or oligosorbents. RAMs, which interact via hydrophobic interactions and a size exclusion effect, found the majority of applications in toxicological and clinical analyses, immunosorbents and oligosorbents synthesized using antibodies and aptamers, respectively, bound to solid support also found numerous applications in food analysis (i.e., immunoaffinity columns for mycotoxins analysis) [21]. The main area in selective sorbent phases, developed since the 1990s, is the construction of MIPs--synthetic materials able to bind target molecules mimicking natural receptors. Manufacturing involves three steps: (i) formation of the pre-polymerization complex between the template and the monomer; (ii) polymerization in the presence of a cross-linker; (iii) removal of the template to give the imprinted polymer (Figure 4) [21]. The analytical potential of MIPs is also related to their commercial availability, where MIPs tailored for analysis of, i.e., specific mycotoxins or bisphenols, are available. In the majority of applications, MIPs are designed for SPE; consequently, molecularly imprinted solid-phase extraction (MISPE) can be realized in two modes: offline and online. The offline process requires the same approach to SPE and the eluate can be analyzed by GC or HPLC, which is automated in the direct coupling of MIPs in the analytical system [155]. MIPs found applications mostly in the analysis of harmful substances in food, such as pesticide residues, veterinary drugs, dyes or toxins. The detailed discussion of the application of MIPs in the detection of the main regulated groups of contaminants has been discussed by [PERSON] et al. [155]. MIPs are used for the analysis of residues in food which are classified by EU Council Directive 96/23/EC: drugs as growth promoters (anabolics, antithyroid agents, beta-agonists), authorized veterinary drugs and contaminants. MIPs have been used for the analysis of stilbenes in fish and milk, \(\beta\)-agonists in pork chloramphenicol in milk and honey [156; 157]. The majority of them were analyzed in MISPE with HPLC to separate the compounds. Similarly, tetracyclines were analyzed in fish, eggs, and chicken muscle using MISPE, but also MIPs on SPME fiber [158]. MIP-SPME mentioned here used for the analysis of tetracycline and related compounds oxytetracycline, doxycycline and chlortetracycline offered LODs in the range of 1-2.3 \(\upmu\)g/L when analyzed by HPLC with a fluorometric detector. Quinolones and fluoroquinolones were determined by MISPE and HPLC in fish, chicken muscle and baby foods. The use of MIPs for d-SPE was also explored for applications in food analysis and used for the detection of dicotyl phthalate in fish [159] and acrylamide in bread [160]. A summary of MISPE and MISPME was presented by [PERSON] et al. [161], with information on herbicides, contaminants, and pharmaceuticals in food samples but also trace metals such as copper ions, selenium and arsenic. Among the 60 papers shown, 4 utilized SPME for MIPS, and the remaining papers mostly used MISPE. Magnetic solid-phase extraction (MSPE) can also benefit from MIPs and procedures were developed for preparing MIPs for the analysis of 17\(\upbeta\)-estradiol in milk, FQs, sulfonamides in chicken breast, curcumin in various foods, malachite green in fish, PCBs, phthalates or mycotoxins [21]. Although MIPs are usually used with solid-phase material and HPLC is usually utilized for compound detection, it can be also used in other approaches as described by [PERSON] et al. [162]. Quartz crystal microbalances (QCMs) were used for the determination of histamine in foods, with a histamine-targeted MIP coated onto the QCM with an LOD of \(10^{-4}\) mg/kg achieved.