MISPE procedure

The principle of MISPE is similar to classical SPE. The different steps in the MISPE method are described in Fig. 18.9 and each step can be optimized for the best performance of the MISPE method. 

Some recent development in the field is discussed in the subsequent paragraphs. 

MIP for diclofenac [DEC] was synthesized by precipitation polymerization [Dai et al., 2011]. The MIP showed high affinity toward DEC in aqueous solution and was used as SPE material for the quantitative enrichment of DEC in environmental water samples. The parameters such as washing solvent, elution solvent and breakthrough volume, which affects the extraction efficiency of the MIPS were evaluated to achieve the selective pre-concentration of DEC from water samples and to reduce non-specific interactions. Recoveries of DEC extracted from tap water, river water and wastewater samples were higher than 95%. The MIPs were found to be highly reusable as the stability of the MIP did not vary even after 30 adsorption and desorption cycles. 

MIPs were used as sorbent material in MISPE for metoclopramlde [MCP] in biological fluids [Javanbakht et al., 2009]. The binding capability and selectivity study of the MIPs revealed the high affinity of MIP for MCP in the aqueous environment. The optimized MISPE procedure was used to selectively extract the MCP from human serum and urine with an extraction recovery of more than 90%. The MISPE procedure resulted in efficient cleanup of trace amounts of MCP from serum and urine and the limits of detection of MCP in human serum and urine were 3 and 1.2 pgL, respectively. 

Lamlvudlne [an antiviral agent with potent activity against AIDS and hepatitis B virus] based MIPs were prepared and applied as sorbent in MISPE of Lamivudine in the biological fluids [human 

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Caro et al. made a noncovalent and a semicovalent MIP, respectively, for 4-nitrophenol (4-NP). Their purpose was to extract selectively 4-NP from river water in the presence of ten other phenolic pollutants. The MIPs were used in an online MISPE procedure employing dichloromethane as wash solvent. Figure 4 (Fig. 1 of the original) shows the experimental setup. The pump on the left is used to deliver the conditioning solutions, the sample, and the wash solvent. The two pumps on the right deliver the organic and the aqueous components of the HPLC... 

These results show that in a MISPE procedure one may encounter substances with different patterns of behavior. In the ideal case the template (or the template and a group of its analogs which need to be carried on for further analysis) are retained 100% during the sample application and the wash step. All other substances (or at least those which interfere with further analysis) should be fully removed. In the non-ideal case some interferents will not be removed by a particular protocol. In this case it is useful to observe the behavior of these interferents on the NIP. If they are retained by the NIP, too, then their retention is likely due to nonspecific binding. In this case a better choice of the solvents in the protocol may help to eliminate the interferent. The danger here is that the new protocol may also reduce the retention of the template and reduce its recovery. It is therefore interesting to note that even in this good paper it has not been shown that the addition of 1 % methanol to the dichloromethane sample was really necessary with the real sample matrices. 

Finally a validation step for the overall MISPE procedure is mandatory to allow the use of the method itself in place of the regulatory methods. The issues to be considered here are the accuracy and precision of the method based on the MISPE protocol, its limit of quantification, selectivity and ruggedness. In particular the inter- and intra-assay precision need to be checked with real samples and certified reference materials and methods [23,24]. 

Ab initio method was used for synthesis of MlPs for furosemide, which is a potent diuretic drug [Bagher et al., 2010]. The AE values were calculated through HF/6-31G[d]. The furosemide interacted more strongly with acrylamide [AAm] in comparison with other functional monomers. Using AAM-based MlPs, a MISPE procedure was developed for the cleanup of furosemide with sufficient accuracy and precision for trace analysis in plasma samples. 

Figure 18.9 MISPE procedures (a] conditioning, (b] sample loading, (c] washing, and (d] elution step.

Figure 11 On-line MISPE procedure. Step 1 sample loading and column washing. Step 2 analyte elution with a plug of desorbing eluent.

Qiao and co-authors reported a new molecularly imprinted solid-phase extraction (MISPE) procedure combined with liquid chromatography for the simultaneous selective extraction and determination of ofloxacin (OFL) and lomefloxacin (LOM)... 

One should note that the MISPE system served two goals here. First, the 10-mL samples were substantially preconcentrated on the MIP. Second, the levels of the other phenolic pollutants were selectively diminished against 4-NP by using the optimized washing procedure. While this example is educative it is not quite clear why the selective wash was needed. Figure 5 (Fig. 2 of the original) shows that the selectivity of HPLC alone was sufficient to determine 4-NP. 

The authors had prepared an MIP imprinted with diazepam, a frequently used benzodiazepine. The MIP did not differentiate between the template and a series of analogs, so those were also retained on the MIP cartridge. The MISPE sample clean-up was followed by HPLC-MS-MS analysis to quantify the drugs. Both the MISPE and a classical SPE procedure were successfully validated. Recoveries of... 

In contrast to the MC-RTP, the MISP-STA is more complex due to the larger number of integer variables to be determined. To solve larger instances, a heuristical procedure can be set up as follows ... 

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