50
S. Iftekhar et al.
There are several approaches for making a MIP based on the types of
interactions that are present between the functional monomers and template
(Huang et al. 2015). In the first approach, covalent bonds are formed between
the template and functional monomers prior to polymerization. This results in
stable interactions between the template and monomers and helps to provide
homogenous binding sites in the final polymer (Martın-Esterban 2013). A limitation of this technique is that the strong interactions between the template and
monomers can sometimes make removal of the template difficult (Huang et al.
2015). An alternative is to use an approach in which the functional monomers
are instead allowed to bind to the template through non-covalent interactions
(e.g., electrostatic forces, van der Waals forces, or hydrogen bonding) (Tamayo et al.
2007; Bergmann and Peppas 2008; Malitesta et al. 2012). This is the most common way for preparing MIPs because it is simple and can result in many interactions
between the functional monomers and template. However, this method can also result
in heterogeneous binding pockets and a decrease in selectivity (Huang et al. 2015).
It is also possible to use a method for MIP preparation that combines covalent and
non-covalent interactions (Fuchs et al. 2012; Zhan et al. 2013).
Many techniques have been employed for synthesizing MIPs with controlled physical properties and sizes. Examples of these techniques are bulk polymerization, suspension polymerization, and precipitation polymerization (Huang et al. 2015). In bulk
polymerization, MIPs are prepared as monoliths by mixing the functional monomers,
template, cross-linking agent, and initiator in a suitable solvent. Suspension polymerization involves polymerization of these components when they are dispersed in
water and in the presence of a surfactant and stabilizer. Precipitation polymerization
is used to synthesize MIP microspheres by dissolving the functional monomers, template, cross-linking agent, and initiator in a large amount of a pore-forming solvent
(Huang et al. 2015).
Most MIPs are used with organic solvents because water tends to disrupt the
interactions that occur between the analyte and support. However, a few reports have
employed aqueous solvents with MIPs (Nelson and Hage 2006; Huang et al. 2015).
MIPs possess excellent stability and good selectivity for their targets, which has
made them of interest as supports for SPE, sensors, and chromatography (Nelson
and Hage 2006). For instance, MIPs can serve as an alternative to immunoaffinity
supports for the detection of analytes against which antibodies may be difficult to
obtain (Nelson and Hage 2006; Huang et al. 2015).
2.3.2 Use of MIPs in Solid-Phase Extraction
Traditional MIPs have been used in many studies for SPE and the selective extraction
of analytes from complex water matrices. For instance, MIPs have been used with
wastewater to extract and detect amphetamines, antidepressants, benzimidazoles,
bisphenol A, β-blockers, carbamazepine, carbaryl, catechols, cyanide, 17β-estradiol,
herbicides, ketoprofen, mercury, sulfonamides, and water-soluble acidic dyes (Say
S. Iftekhar et al.
There are several approaches for making a MIP based on the types of
interactions that are present between the functional monomers and template
(Huang et al. 2015). In the first approach, covalent bonds are formed between
the template and functional monomers prior to polymerization. This results in
stable interactions between the template and monomers and helps to provide
homogenous binding sites in the final polymer (Martın-Esterban 2013). A limitation of this technique is that the strong interactions between the template and
monomers can sometimes make removal of the template difficult (Huang et al.
2015). An alternative is to use an approach in which the functional monomers
are instead allowed to bind to the template through non-covalent interactions
(e.g., electrostatic forces, van der Waals forces, or hydrogen bonding) (Tamayo et al.
2007; Bergmann and Peppas 2008; Malitesta et al. 2012). This is the most common way for preparing MIPs because it is simple and can result in many interactions
between the functional monomers and template. However, this method can also result
in heterogeneous binding pockets and a decrease in selectivity (Huang et al. 2015).
It is also possible to use a method for MIP preparation that combines covalent and
non-covalent interactions (Fuchs et al. 2012; Zhan et al. 2013).
Many techniques have been employed for synthesizing MIPs with controlled physical properties and sizes. Examples of these techniques are bulk polymerization, suspension polymerization, and precipitation polymerization (Huang et al. 2015). In bulk
polymerization, MIPs are prepared as monoliths by mixing the functional monomers,
template, cross-linking agent, and initiator in a suitable solvent. Suspension polymerization involves polymerization of these components when they are dispersed in
water and in the presence of a surfactant and stabilizer. Precipitation polymerization
is used to synthesize MIP microspheres by dissolving the functional monomers, template, cross-linking agent, and initiator in a large amount of a pore-forming solvent
(Huang et al. 2015).
Most MIPs are used with organic solvents because water tends to disrupt the
interactions that occur between the analyte and support. However, a few reports have
employed aqueous solvents with MIPs (Nelson and Hage 2006; Huang et al. 2015).
MIPs possess excellent stability and good selectivity for their targets, which has
made them of interest as supports for SPE, sensors, and chromatography (Nelson
and Hage 2006). For instance, MIPs can serve as an alternative to immunoaffinity
supports for the detection of analytes against which antibodies may be difficult to
obtain (Nelson and Hage 2006; Huang et al. 2015).
2.3.2 Use of MIPs in Solid-Phase Extraction
Traditional MIPs have been used in many studies for SPE and the selective extraction
of analytes from complex water matrices. For instance, MIPs have been used with
wastewater to extract and detect amphetamines, antidepressants, benzimidazoles,
bisphenol A, β-blockers, carbamazepine, carbaryl, catechols, cyanide, 17β-estradiol,
herbicides, ketoprofen, mercury, sulfonamides, and water-soluble acidic dyes (Say