MIPs imprinting factor

A means to avoid such tedious optimization can be envisaged by employing stoichiometric monomers to develop strong interactions with the template as mentioned above. The other way is to incorporate hydrophilic comonomers (2-hydroxyethyl methacrylate (HEMA), acrylamide) or cross-linkers (pentaerythri-toltriacrylate, methylene bisacrylamide) in the polymer. This results in an increase of the hydrophilicity of the polymer. Indeed, the use of HEMA for a MIP directed towards the anesthetic bupivacaine resulted in high imprinting factors due to reduced non-specific hydrophobic adsorption in aqueous buffer. This was not the case when HEMA was omitted from the polymerization mixture [27]. These conditions were exploited for the direct and selective extraction of bupivacaine from blood plasma samples. 

Fig. 5.32. Influence of hydrogen bond donor number of the mobile phase modifier on the capacity factor ( l) of BOC-r-phenylalanine injected (10 pg) on a MIP imprinted with the r-enantiomer. Mobile phase dichloromethane containing different amounts of the polar modifiers. Reproduced from Allender et al. [47].

Fig. 5.34. Retention (k ) of D- and L-PA and BA on (A) an L-PA MIP PLPA and (B) a MIP imprinted with BA PBA, injecting 100 nmol solute versus mobile phase apparent pH (pHapp). (C) and (D) show the corresponding separation factors (a) obtained at two different sample loads. The separation factor of D,L-PA (C) was calculated as a = k l lk o and of BA (100 nmol) (D) as a = /t eAfon PBA)/fc BA(on PLPA). From Sellergren and Shea [129].

The use of MIPs as chromatographic stationary phases is the most studied application of MIPs. This method is, in fact, the best way to quickly and efficiently validate the performance of a developed MIP. To achieve this, the MIP is packed into an HPLC column and the retention characteristics of the template and/or analogue molecules are collected in various selected mobile phases. From the collected data, useful parameters, such as capacity factor, imprinting factor, and peak asymmetry, are calculated and used to evaluate polymer affinity, cross reactivity, and other features of the MIP. 

Prediction of imprinting factor of MIPs and study Atropine and Boc-L-Trp of template monomer complexes d-Brompheniramine76,77... 

Fig. 7.6 Options to assess imprinting effects and corresponding response factors, (a) Static mode assessment. (1) Template release. K = partitioning coefficient. (2) Comparison of template binding to a MIP with that to a NIP. IF = imprinting factor. (3) Comparison of binding of template with that of a close analog to the MIP. a = selectivity factor, (b) Flow through SPE mode assessment. Response factors can here be the % recovered template and for gradient elution, the cumulative recovery...

The amount of P-estradiol bound to each MIP and NIP (as an average of four replicas) is seen in Fig. 7.12 together with the corresponding imprinting factors. 

Fig. 7.12 (a) Amount of P-estradiol bound to MIPs and NIPs of an 80-polymer library. The results are averages of four replicas with the standard deviations given as error bars, (b) Average imprinting factors (IF = n p/n ) obtained for the monomer library using the parallel evaluation technique with reader or the serial technique with HPLC... 

Fig. 7.14 3D-representation of imprinting factors (IF) obtained from the rebinding of BV in phosphate buffer pH 7.4 to the polymer library prepared from the design shown in Fig. 7.13. Arrows indicate compositions selected for upscaling as well as the conventional composition used to produce the previously reported MIP...

Fig. 7.15 Approach to assess a MIP/NIP library in the SPE mode. After quantitative nonspecific adsorption of the analyte from water the analyte is gradually eluted from the cartridge by increasing the acetonitrile content in the wash steps. The cumulative recovery is plotted against % acetonitrile in the wash step. The hydrophihcity index is defined as the % water present in the wash solvent leading to 50% release of the analyte from the NIP. The cumulative imprinting factor is defined as the ratio of the recovery from the NIP at that point (=50%) over that from the MIP (= Y)...

Based on this study, the MIPs were synthesized and binding performance was evaluated. The imprinting factor for AA and AAm based MIPs were 5.28 and 4.80, respectively, 4-Vp based MIP had imprinting factor of 2.59 while MMA based MIP exhibited an imprinting factor of 1.95. The experimental results were in good agreement with the computational predictions. 

The thus calculated partition coeificients K (A mip and. np) and imprinting factors are the most important responses used to evaluate the polymers. Alternatively, the fluorescence intensity of each polymer upon binding of the template has been used as response (for an example see Refs. 9 and 10). 

After complete extraction of the template, the polymers were submitted to equilibrium batch rebinding with a ImM solution of terbutylazine in CH2CI2. The imprinting factors ( mip/ np) of MIPs prepared using MAA and TFM as functional monomers were 11 and 6, respectively. 

Think about the final application of the materials you want to prepare or about the way you want to characterize them. If you evaluate the MIPs by batch rebinding, choose partition coefficients or the imprinting factors IF. If you also evaluate them as stationary phases, choose the capacity factors. 

MIPS prepared with this monomer showed relatively high imprinting factors and a degree of selectivity for barbital over differently substituted barbiturates when tested in the chromatographic mode. Further, analytes where some of the hydrogen-bonding sites had been removed were much less retained on these polymers. 

Leonhardt et al were able to show a specific hydrolytic effect when treating nitrophenyl esters with an MIP imprinted with pyridine derivatives of N-boc-amino acids using DVB and 4(5)-vinylimidazole as monomers in combination with chelated Co ions. Compared to the control polymer, hydrolysis was accelerated by a factor of 4 to 5, while a comparison with MIP imprinted with other pyridine derivatives of N-boc-amino acids only gave an acceleration of the reaction by a factor of 2 to 3. Robinson et al used phosphonates as TSA and showed a catalytic effect of an MIP imprinted with p-nitrophenylmethyl phosphonate, using 4(5)-vinylimidazole and Co ions, on the hydrolysis of p-nitrophenol acetate. The authors— aware of the fact that imidazole containing polymers in general exhibit catalytic effects—could nevertheless demonstrate that the imprinted specimens were of 60% higher activity than the control polymers. 

Not only chiral separations have been achieved with Mi-stationary phases. It has also been demonstrated that the MIP could distinguish between ortho- and para-isomers of carbohydrate derivatives. For example, a polymer imprinted with o-aminophenyl tetraacetyl P-D-galactoside was used to analyze a mixture of p-and o-aminophenyl tetraacetyl P-D-galactoside. As expected, the imprinted ortho analyte eluted after the non-imprinted para component see Fig. 5. Although baseline separation was not obtained, a separation factor of a = 1.51 was observed [19]. 

In a different approach, Lin et al. have used particles derived from a ground MI-bulk polymer and mixed with a polyacryl amide gel for chiral separation. Using a polymer imprinted with L-phenylalanine, D-phenylalanine could be separated from the template with a separation factor of 1.45 [35]. Although the combination of MIP with capillary electrochromatography is still not widely used, the ability to separate enantiomers in nanoliter samples promises interesting developments for the future. 

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