## 5 MIP Applications for the Extraction of Antibiotics in Milk
### Tetracyclines
The developed MIP-HCMs demonstrated higher adsorption capacity and selectivity than the corresponding NIP-HCMs. Furthermore, the MIP-HCMs displayed great rebinding ability by selectively interacting and trapping the analytes in the imprinted sites [73]. A MISPE-HPLC-UV method was developed for the determination of OTC, metacycline (MTC) and DC. OTC (0.160 g) and MAA (0.207 mL) were dissolved in acetonitrile (1.125 mL) and the mixture was incubated at room temperature for 1 h. KH-570 (0.554 mL) and AIBN (0.068 g) were added and the mixture was sonicated for 2 min and stirred under nitrogen stream at 53.8 \({}^{\circ}\)C for 3 h. TEOS (2.73 mL) dissolved in ethanol (5.60 mL) and hydrolyzed with HCl (0.1 mL) was added and the mixture was stirred at 60 \({}^{\circ}\)C for 3 h. The mixture was adjusted to pH 6.0 with sodium hydroxide solution and evaporated at 65 \({}^{\circ}\)C. The developed MIP-HCM was grinded into particles of (38.5-63) \(\upmu\)m size and the template was removed by Soxhlet extraction with methanol-acetic acid (4:1, \(v/v\)) for 24 h. The MIP-HCM particles were washed with methanol and dried under vacuum at 60 \({}^{\circ}\)C for 24 h. OTC-MIP-HCM particles (50 mg) were packed into an empty SPE cartridge, preconditioned with water-acetic acid (90:10, \(v/v\); 3 mL), water (3 mL), methanol (3 mL) and cyclohexane (3 mL), loaded with pretreated spiked milk extract (4 mL) and washed with toluene-methanol (85:15, \(v/v\); 1 mL). The analytes were eluted with methanol-acetic acid (60:40, \(v/v\); 2 mL), the eluate was evaporated under nitrogen stream and the dry residue was reconstituted with mobile phase. In comparison with the respective NIP, MIP adsorption capacity for OTC was higher, with Qmax values of 46,650 and 64,800 \(\upmu\)g/g [74]. The same MIP-HCM preparation protocol was followed for the preparation of TC-MIP-HCM particles, utilized for the development of a MISPE-HPLC-UV method for the determination of TC, OTC and demeclocycline (DMC) in egg, milk, and milk powder. A pre-column was packed with TC-MIP-HCM particles and connected to an on-line SPE-HPLC system. The pre-column was conditioned with water (2 mL), loaded with pretreated milk extract and washed with methanol-water (5:95, \(v/v\)). The analytes were eluted with methanol-acetonitrile-oxalic acid (5:25:70, \(v/v/v\)). Dynamic adsorption capacity for TC was 1790 \(\upmu\)g/g [75]. A PMME-HPLC-UV method was developed for the determination of TC, OTC, CTC and minocycline (MC), utilizing MC-imprinted poly(methacrylic acid-KH-570-graphene oxide-\(N\),\(N^{\prime}\)-methylenebisacrylamide) monoliths. MAA (15 \(\upmu\)L), \(N\),\(N^{\prime}\)-methylenebisacrylamide (MBA) (0.03 g), AIBN (5 mg), KH-570-graphene oxide nanosheets (0.005 g) were dissolved in dimethylsulfoxide (375 mL) with polyethylene glycol (0.11 g) and the mixture was degassed by sonication for 30 min. The mixture was transferred and sealed inside a pretreated capillary and polymerization was carried out at 55 \({}^{\circ}\)C for 24 h. The capillary was washed with methanol, MC was pumped through the capillary for 2 h and the excess of MC was removed by pumping tris(hydroxymethyl)aminomethane-HCl buffer (10 mM, pH 8.0) through the monolith. Tris(hydroxymethyl)aminomethane-HCl buffer (10 mM, pH 8.0; 1 mL) that contained dopamine and ammonium persulphate was pumped though the capillary for 15 min so that a polydopamine film was attached on the surface of the developed MIP monolith. The template was removed by washing the monolith with oxalic acid-methanol-acetonitrile (70:10:20, \(v/v/v\)). The developed MC imprinted monolith was preconditioned with methanol for 10 min, loaded with pretreated spiked milk extract for 25 min and the analytes were eluted with oxalic acid-methanol-acetonitrile (70:10:20, \(v/v/v\)). In comparison with the respective NIP, MIP adsorption capacities for TC, OTC, CTC and MC ranged between (21.28-40.43) \(\upmu\)g/g, while the imprinting factors ranged between (1.37-1.89) [76].