Selective sample treatment using molecularly imprinted polymers

Synthesis and evaluation of a molecularly imprinted polymer for selective solid-phase extraction of irinotecan from human serum samples

A molecularly imprinted polymer (MIP) was synthesized by non-covalent imprinting polymerization using irinotecan as template. Methacrylic acid and 4-vinylpyridine were selected as functional monomers. An optimized procedure coupled to LC-PDA analysis was developed for the selective solid-phase extraction of irinotecan from various organic media. A specific capacity of 0.65 µmol·g⁻¹ for the MIP was determined. The high specificity of this MIP was demonstrated by studying the retention behaviour of two related compounds, camptothecin and SN-38. This support was applied for the extraction of irinotecan from human serum samples.

Molecularly imprinted polymers: present and future prospective

Molecular Imprinting Technology (MIT) is a technique to design artificial receptors with a predetermined selectivity and specificity for a given analyte, which can be used as ideal materials in various application fields. Molecularly Imprinted Polymers (MIPs), the polymeric matrices obtained using the imprinting technology, are robust molecular recognition elements able to mimic natural recognition entities, such as antibodies and biological receptors, useful to separate and analyze complicated samples such as biological fluids and environmental samples. The scope of this review is to provide a general overview on MIPs field discussing first general aspects in MIP preparation and then dealing with various application aspects. This review aims to outline the molecularly imprinted process and present a summary of principal application fields of molecularly imprinted polymers, focusing on chemical sensing, separation science, drug delivery and catalysis. Some significant aspects about preparation and application of the molecular imprinting polymers with examples taken from the recent literature will be discussed. Theoretical and experimental parameters for MIPs design in terms of the interaction between template and polymer functionalities will be considered and synthesis methods for the improvement of MIP recognition properties will also be presented.

Synthesis of homoveratric acid-imprinted polymers and their evaluation as selective separation materials

A bulk polymerization method was used to easily and efficiently prepare homoveratric acid (3,4-dimethoxyphenylacetic acid)-imprinted polymers from eight basic monomers: 2-vinylpyridine, 4-vinylpyridine, 1-vinylimidazole, N-allylaniline, N-allylpiperazine, allylurea, allylthiourea, and allylamine, in the presence of homoveratric acid as a template in N,N-dimethylformamide as a porogen. The imprinted polymer prepared from allylamine had the highest affinity to the template, showing an imprinting factor of 3.43, and allylamine polymers MIP8/NIP8 were selected for further studies. Their binding properties were analyzed using the Scatchard method. The results showed that the imprinted polymers have two classes of heterogeneous binding sites characterized by two pairs of K(d), B(max) values: K(d)(1) = 0.060 μmol/mL, B(max)(1) = 0.093 μmol/mg for the higher affinity binding sites, and K(d)(2) = 0.455 μmol/mL, B(max)(2) = 0.248 μmol/mg for the lower affinity binding sites. Non-imprinted polymer has only one class of binding site, with K(d) = 0.417 μmol/mL and B(max) = 0.184 μmol/mg. A computational analysis of the energies of the prepolymerization complexes was in agreement with the experimental results. It showed that the selective binding interactions arose from cooperative three point interactions between the carboxylic acid and the two methoxy groups in the template and amino groups in the polymer cavities. Those results were confirmed by the recognition studies performed with the set of structurally related compounds. Allylamine polymer MIP8 had no affinity towards biogenic amines. The obtained imprinted polymer could be used for selective separation of homoveratric acid.

An overview of matrix effects in liquid chromatography-mass spectrometry

Matrix-dependent signal suppression or enhancement represents a major drawback in quantitative analysis with liquid chromatography coupled to atmospheric pressure ionization mass spectrometry (LC-API-MS). Because matrix effects (ME) might exert a detrimental impact on important method parameters (limit of detection, limit of quantification, linearity, accuracy, and precision), they have to be tested and evaluated during validation procedure. This review gives a detailed description on when these phenomena might be expected, and how they can be evaluated. The major sources of ME are discussed and illustrated with examples from bioanalytical, pharmaceutical, environmental, and food analysis. Because there is no universal solution for ME, the main strategies to overcome these phenomena are described in detail. Special emphasis is devoted to the sample-preparation procedures as well as to the recent improvements on chromatographic and mass spectrometric conditions. An overview of the main calibration techniques to compensate for ME is also presented. All these solutions can be used alone or in combination to retrieve the performance of the LC-MS for a particular matrix-analyte combination.

Novel extraction supports based on immobilised aptamers: evaluation for the selective extraction of cocaine

A new kind of selective sorbent based on the use of aptamers and dedicated to the selective solid phase extraction was developed. Cocaine aptamer was chosen as model aptamer to demonstrate the feasibility of this material and to provide a complete evaluation of the synthesized sorbent. The effect of different parameters such as the nature of the immobilisation support (silica, agarose), the type of immobilisation (covalent or non-covalent) and the length of the spacer arm (C(6) or C(12)) were studied. Therefore, various oligosorbents based on different immobilisation strategies were synthesized and characterised by estimating the extraction recovery and the capacity of cocaine and the binding efficiency of aptamers. Control supports without immobilised aptamers were simultaneously studied in parallel to assess the selectivity brought by the oligosorbents. The oligosorbent based on CNBr-activated sepharose showed the best performances with an extraction recovery for cocaine of 90% while 6% was obtained on the control sorbent. The high selectivity brought by the oligosorbent was then illustrated by applying the oligoextraction followed by LC/MS analysis to a post-mortem blood (cocaine overdose). Results were compared to those resulting from a conventional protein precipitation procedure. The presence of co-extracted interfering compounds was strongly reduced with the treatment by oligoextraction. A limit of quantification of 0.5 ng/mL was obtained that is largely lower than the concentration found after a single intake of cocaine.

Preparation of dummy template imprinted polymers at surface of silica microparticles for the selective extraction of trace bisphenol A from water samples

Molecularly imprinted polymers for bisphenol A (BPA) were prepared by using surface molecular imprinting technique. Analogues of BPA, namely 4,4'-dihydroxybiphenyl and 3,3',5,5'-tetrabromobisphenol A, were used as the dummy templates instead of BPA, to avoid the leakage of a trace amount of the target analyte (BPA). The resulting dummy molecularly imprinted polymers (DMIPs) showed the large sorption capacity, high recognition ability and fast binding kinetics for BPA. The maximal sorption capacity was up to 958 micromol g(-1), and it only took 40 min for DMIPs to achieve the sorption equilibrium. The DMIPs were successfully applied to the solid-phase extraction coupled with HPLC/UV for the determination of BPA in water samples. The calibration graph of the analytical method was linear with a correlation coefficient more than 0.999 in the concentration range of 0.0760-0.912 ng mL(-1) of BPA. The limit of detection was 15.2 pg mL(-1) (S/N=3). Recoveries were in the range of 92.9-102% with relative standard deviation (RSD) less than 11%. The trace amounts of BPA in tap water, drinking water, rain and leachate of one-off tableware were determined by the method built, and the satisfactory results were obtained.

Determination of cocaine in human plasma by selective solid-phase extraction using an aptamer-based sorbent

A complete characterization is presented of a highly selective solid-phase extraction (SPE) sorbent which exploits the properties of aptamers. An oligosorbent based on aptamers immobilized on a solid support was synthesized and tested for the selective extraction of cocaine from human plasma. Anticocaine aptamers were immobilized to CNBr-activated Sepharose, and an extraction procedure was developed in pure media. Specific retention of cocaine on the oligosorbent was demonstrated, and the capacity of the support was determined. This oligosorbent was then applied to the selective extraction of cocaine from plasma at a concentration of 0.4 mg L(-1), i.e., corresponding to the plasma concentration reached after an intake of a single dose of cocaine. Extraction recovery close to 90% was obtained. Moreover, interfering compounds that perturbed cocaine quantification when using a standard SPE sorbent were not retained on the oligosorbent, thus allowing fast and reliable analyses of plasma samples with an estimated limit of detection of 0.1 microg mL(-1).

Online hyphenation of multimodal microsolid phase extraction involving renewable molecularly imprinted and reversed-phase sorbents to liquid chromatography for automatic multiresidue assays

Molecular imprinted polymers (MIP) have recently drawn much attention as highly selective solid-phase materials for handling and isolation of organic pollutants in complex matrices. Because of the impaired retention capacity for target species as compared with reversed-phase materials and irreversible sorption of interfering compounds by nonspecific interactions, the implementation of MIP-based solid-phase reactors as permanent components in automatic flow-systems has not received widespread acceptance as of yet. To tackle this limitation, a dynamic microscale solid phase extraction (microSPE) method capitalizing on the principle of programmable flow and bead injection analysis is herein proposed as a front end to liquid chromatography for multiresidue assays. It involves in-line renewable tandem-SPE microcolumns composed of molecularly imprinted polymers and copolymeric N-vinylpyrrolidone/divinylbenzene beads integrated within the flow network for multimodal extraction. Chlorotriazine herbicides (namely, atrazine, simazine, propazine) and principal degradation products thereof (namely, deisopropylatrazine and deethylatrazine) were selected as model analytes. The effect of several parameters, including the dimensions and chemical composition of the sorptive microcolumns, the sample loading flow rate, the type and volume of eluent, the interface with liquid chromatography (LC), and the disposable nature of the column on the analytical performance were investigated in detail. The assembled flow setup features appropriate removal of interfering organic species via solvent switch with toluene, the circumvention of analyte band-broadening in LC by in-line merging of the eluate with a water stream, and the transfer of the overall analyte-containing eluate into the LC. For 10-mL sample percolation, limits of detection (S/N = 3) of 0.02-0.04 ng mL(-1), limits of quantification (S/N = 10) of 0.07-0.12 ng mL(-1), absolute recovery percentages >79%, precision within 1.4-5.5%, and enrichment factors of 46-49 were obtained for the suite of assayed herbicides. The multimodal microSPE method with renewable beads was applied to the multiresidue determination of the target herbicides in crude soil extracts and untreated environmental waters at concentration levels below those endorsed by the current EU Water Framework Directives following appropriate sample preconcentration and/or cleanup.

Molecularly imprinted polymers for ochratoxin a extraction and analysis

Molecularly imprinted polymers (MIPs) are considered as polymeric materials that mimic the functionality of antibodies. MIPs have been utilized for a wide variety of applications in chromatography, solid phase extraction, immunoassays, and sensor recognition. In this article, recent advances of MIPs for the extraction and analysis of ochratoxins are discussed. Selection of functional monomers to bind ochratoxin A (OTA) with high affinities, optimization of extraction procedures, and limitations of MIPs are compared from different reports. The most relevant examples in the literature are described to clearly show how useful these materials are. Strategies on MIP preparation and schemes of analytical methods are also reviewed in order to suggest the next step that would make better use of MIPs in the field of ochratoxin research. The review ends by outlining the remaining issues and impediments.

A review of the analysis of tobacco-specific nitrosamines in biological matrices

Tobacco use constitutes a leading cause of mortality and morbidity worldwide. Tobacco-specific nitrosamines (TSNAs) are an important class of biomarkers for tobacco carcinogen uptake. The current review focuses on the issues and developments in analysis of these compounds in human biological matrices. The two most widely used techniques for TSNA bioanalysis are gas chromatography coupled with thermal energy analysis and liquid chromatography coupled with mass spectrometry, employing various sample preparation techniques. The review provides an overview of the tools and techniques currently available for TSNA bioanalysis that will help towards the ultimate goal of understanding the mechanisms of cancer caused by the use of tobacco products. A contrast and comparison of the important aspects of bioanalysis such as sample preparation, compound detection, and throughput is discussed for the thermal energy analysis- and mass spectrometry-based techniques. Complex sample extraction procedures, throughput, and the ability to validate are important issues of concern for the gas chromatography-thermal energy analysis-based methods. On the other hand, addressing ion suppression matrix effects remains an important challenge for hyphenated mass spectrometry-based methods. The review also provides an extensive summary of analytical procedures for various studies measuring tobacco-specific nitrosamines in different biological matrices.

Exploiting automatic on-line renewable molecularly imprinted solid-phase extraction in lab-on-valve format as front end to liquid chromatography: application to the determination of riboflavin in foodstuffs

In the present work, it is proposed, for the first time, an on-line automatic renewable molecularly imprinted solid-phase extraction (MISPE) protocol for sample preparation prior to liquid chromatographic analysis. The automatic microscale procedure was based on the bead injection (BI) concept under the lab-on-valve (LOV) format, using a multisyringe burette as propulsion unit for handling solutions and suspensions. A high precision on handling the suspensions containing irregularly shaped molecularly imprinted polymer (MIP) particles was attained, enabling the use of commercial MIP as renewable sorbent. The features of the proposed BI-LOV manifold also allowed a strict control of the different steps within the extraction protocol, which are essential for promoting selective interactions in the cavities of the MIP. By using this on-line method, it was possible to extract and quantify riboflavin from different foodstuff samples in the range between 0.450 and 5.00 mg L(-1) after processing 1,000 microL of sample (infant milk, pig liver extract, and energy drink) without any prior treatment. For milk samples, LOD and LOQ values were 0.05 and 0.17 mg L(-1), respectively. The method was successfully applied to the analysis of two certified reference materials (NIST 1846 and BCR 487) with high precision (RSD < 5.5%). Considering the downscale and simplification of the sample preparation protocol and the simultaneous performance of extraction and chromatographic assays, a cost-effective and enhanced throughput (six determinations per hour) methodology for determination of riboflavin in foodstuff samples is deployed here.

Molecularly imprinted layer-coated silica nanoparticles for selective solid-phase extraction of bisphenol A from chemical cleansing and cosmetics samples

Highly selective molecularly imprinted layer-coated silica nanoparticles for bisphenol A (BPA) were synthesized by molecular imprinting technique with a sol-gel process on the supporter of silica nanoparticles. The BPA-imprinted silica nanoparticles were characterized by fourier transform infrared spectrometer, transmission electron microscope, dynamic adsorption and static adsorption tests. The equilibrium association constant, K(a), and the apparent maximum number of binding sites, Q(max), were estimated to be 1.25 x 10(5) mL micromol(-1) and 16.4 micromol g(-1), respectively. The BPA-imprinted silica nanoparticles solid-phase extraction (SPE) column had higher selectivity for BPA than the commercial C18-SPE column. The results of the study indicated that the prepared BPA-imprinted silica nanoparticles exhibited high adsorption capacity and selectivity, and offered a fast kinetics for the rebinding of BPA. The BPA-imprinted silica nanoparticles were successfully used in SPE to selectively enrich and determine BPA from shampoo, bath lotion and cosmetic cream samples.

Molecularly imprinted polymer for analysis of trace atrazine herbicide in water

A molecularly imprinted polymer (MIP) for atrazine was synthesized by non-covalent method. The binding capacity of MIP was 1.00 mg g(-1) polymer. The selectivity and recovery were investigated with various pesticides which are mostly, found in the environment, for both similar and different chemical structure of atrazine. The competitive recognition between atrazine and structurally similar compounds was evaluated and it was found that the system provided highest recovery and selectivity for atrazine while low recovery and selectivity were obtained for the other compounds. The highest recovery was obtained from MIP compared with non-imprinted polymer (NIP), a commercial C(18) and a granular activated carbon (GAC) sorbent. The method provided high recoveries ranged from 94 to 99% at two spiked levels with relative standard deviations less than 2%. The lower detection limit of the method was 80 ng L(-1). This method was successfully applied for analysis of environmental water samples.