Selective solid-phase extraction of amoxicillin and cephalexin from urine samples using a molecularly imprinted polymer

In this paper we describe, for the first time, a molecularly imprinted polymer (MIP) for the antibiotic amoxicillin (AMX), synthesised by a noncovalent molecular imprinting approach and used to extract AMX selectively from urine samples. The MIP was applied as a molecularly selective sorbent in molecularly imprinted SPE (MISPE) in an off-line mode, where it showed useful cross-selectivity for a structurally related antibiotic, cephalexin (CPX). By using a MISPE protocol, the MIP was able to selectively extract both AMX and CFX from 5 mL of water spiked with 10 mg/L with recoveries of 75 and 78% for AMX and CFX, respectively. When applied to real samples (urine) at clinically relevant concentrations, recoveries from 2 mL of human urine spiked with 20 mg/L decreased slightly to 65 and 63% for AMX and CFX, respectively. To demonstrate further the selectivity of the MIP obtained, a comparison with commercially available SPE cartridges was performed. Improvements in the retention of both AMX and CFX on the MIP were obtained relative to the commercially available cartridges, and the MISPE extracts were considerably cleaner, due to molecularly selective analyte binding by the MIP.     

Molecularly imprinted solid-phase extraction for the selective determination of 17β-estradiol in fishery samples with high performance liquid chromatography

A molecularly imprinted polymer (MIP) has been synthesized by a thermo-polymerization method using methacrylic acid (MAA) as functional monomer, ethylene glycol dimethacrylate (EGDMA) as cross-linker, acetonitrile as porogenic solvent, and 17β-estradiol as template. The MIP showed obvious affinity for 17β-estradiol in acetonitrile solution, which was confirmed by absorption experiments. After optimization of molecularly imprinted solid-phase extraction (MISPE) conditions, three structurally related estrogenic compounds (17β-estradiol, estriol, and diethylstilbestrol) were used to evaluate the selectivity of the MIP cartridges. The MIP cartridges exhibited highly selectivity for E₂, the recoveries were 84.8 ± 6.53% for MIPs and 19.1 ± 1.93% for non-imprinted polymer (NIP) cartridges. The detection and quantification limits correspond to 0.023 and 0.076 mg L⁻¹. Furthermore, the MISPE methods were used to selectively extract E₂ from fish and prawn tissue prior to HPLC analysis. This MISPE-HPLC procedure could eliminate all matrix interference simultaneously and had good recoveries (78.3-84.5%).     

Development of a selective molecularly imprinted polymer-based solid-phase extraction for indomethacin from water samples

A selective molecularly imprinted solid-phase extraction (MISPE) for indomethacin (IDM) from water samples was developed. Using IDM as template molecule, acrylamide (AM) or methacrylic acid (MAA) as functional monomer, ethylene dimethacrylate (EDMA) as crosslinker, and bulk or suspension polymerization as the synthetic method, three molecularly imprinted polymers (MIPs) were synthesized and characterized with a rebinding experiment. It was found that the MIP of AM-EDMA produced by bulk polymerization showed the highest binding capacity for IDM, and so it was chosen for subsequent experiments, such as those testing the selectivity and recognition binding sites. Scatchard analysis revealed that at least two kinds of binding sites formed in the MIP, with the dissociation constants of 7.8 μmol L⁻¹ and 127.2 μmol L⁻¹, respectively. Besides IDM, three structurally related compounds — acemetacin, oxaprozin and ibuprofen — were employed for selectivity tests. It was observed that the MIP exhibited the highest selective rebinding to IDM. Accordingly, the MIP was used as a solid-phase extraction sorbent for the extraction and enrichment of IDM in water samples. The extraction conditions of the MISPE column for IDM were optimized to be: chloroform or water as loading solvent, chloroform with 20% acetonitrile as washing solution, and methanol as eluting solvent. Water samples with or without spiking were extracted by the MISPE column and analyzed by HPLC. No detectable IDM was observed in tap water and the content of IDM in a river water sample was found to be 1.8 ng mL⁻¹. The extraction efficiencies of the MISPE column for IDM in spiked tap and river water were acceptable (87.2% and 83.5%, respectively), demonstrating the feasibility of the prepared MIP for IDM extraction. Figure Molecularly imprinted polymer-based solid-phase extraction for indomethacin     

Molecularly Imprinted Polymers as Specific Adsorbents for Zearalenone Produced by Precipitation Polymerization and Applied to Mycotoxin Production

In this work, molecularly imprinted polymers (MIPs) using the mycotoxin zearalenone (ZEA) as template were first synthesized via precipitation polymerization and then applied as specific adsorbents in molecularly imprinted solid-phase extraction (MISPE) cartridges. The MISPE procedure was optimized with 3 mL of acetonitrile for preconditioning, 1 mL of acetonitrile:H₂O (60:40) for loading, 1 mL of acetonitrile:H₂O (30:70), and 3 mL of methanol:acetic acid (95:5) for elution. The obtained MIPs showed high selectivity of 96.9% towards ZEA, and low cross-reactivity (1-20%) to other Fusarium mycotoxins including deoxynivalenol, nivalenol, HT-2 toxin and T-2 toxin. The cross-reactivity to fumonisin B₁ amounted to 61%. The MISPE was applied for enrichment of ZEA, which was produced by Fusarium graminearum strains. An enrichment factor above 50 was reached. Recoveries of 1 µg/mL were between 90.8% and 99.6%. A small amount of ZEA was produced by 9 F. graminearum strains with a maximum of 13 µg, then purified by the developed MISPE and analyzed by LC-MS/MS.     

Molecularly imprinted solid-phase extraction of (-)-ephedrine from Chinese Ephedra

Method of molecularly imprinted solid phase extraction (MISPE) of (-)-ephedrine from Chinese Ephedra has been developed in the research. The molecularly imprinted polymer (MIP) with good selectivity and affinity for (-)-ephedrine was synthesized with (-)-ephedrine as the template, methacrylic acid as the functional monomer. The washing and elution conditions in MISPE were selected and optimized for efficient analyte extraction and sample clean-up. A clean analytical HPLC base line of ephedra extract was obtained after MISPE, which indicated that the sample pre-treatment was efficient. Good recovery and precision were obtained in the assessment for the MISPE-HPLC procedure, which demonstrated it is a reliable method and can be used for the determination of (-)-ephedrine in herbal ephedra.     

Size-exclusion chromatography in 1,1,1,3,3,3-hexafluoro-2-propanol

Two molecularly imprinted polymers (MIPs) have been synthesised for the selective extraction of 4-nitrophenol (4-NP) from water samples. One polymer was synthesised via a non-covalent approach and the other via a semi-covalent approach. The selectivity of the polymers for 4-NP was evaluated when these polymers were applied in on-line solid-phase extraction (MISPE) coupled to reversed-phase HPLC. The MISPE conditions for both MIPs were optimised and a clean-up step was included to eliminate non-specific interactions. Differences between the two MIPs were observed with the non-covalent MIP being the more selective of the two, whereas the recoveries were slightly higher for the semi-covalent MIP. The performance of the imprinted polymers in the MISPE of real water samples was also evaluated.     

Solid-phase extraction using a molecularly imprinted polymer for the selective purification and preconcentration of norfloxacin from seawater

Abstract

A highly selective and effective method for the purification and preconcentration of norfloxacin (NFX) in seawater samples was developed based on molecularly imprinted solid-phase extraction (MISPE). The molecularly imprinted polymer was synthesized by precipitation polymerization. Methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) were used as the functional monomer and crosslinker, respectively. The resulting molecularly imprinted polymer (MIP) showed high adsorption for NFX and was selective for its solid-phase extraction. An offline MISPE method followed by high performance liquid chromatography with diode array detection was established for the determination of NFX in seawater. The recoveries of spiked seawater samples using the MISPE columns were satisfactorily higher than 77.6%. The relative standard deviation was less than 5.60%, and the limit of detection was 0.027?μg L^?1. Four seawater samples obtained from the Bohai Sea were analyzed, and NFX was found only at one location at a concentration of 0.280?μg L^?1.     

Molecularly imprinted solid-phase extraction for the selective HPLC determination of ractopamine in pig urine

A method was developed for the determination of ractopamine in pig urine using molecularly imprinted solid-phase extraction (MISPE) as the sample clean-up technique combined with high-performance liquid chromatography. The molecularly imprinted polymer (MIP) was synthesized in acetonitrile-triethylamine system using ractopamine (RAC) as the template and acrylamide as the monomer. The binding capacity of the polymer toward RAC was found to be about 2.57 mg of ractopamine/g of polymer. The optimal procedures for MISPE consisted of conditioning with 3 mL methanol, equilibrating with 3 mL of water, loading volume of <10 mL of aqueous sample (pH 7), washing with 3 mL water and 3 mL methanol, and eluting with 5 mL of 5% ammonia in methanol. In the four spiked samples with the levels of 0.01, 0.1, 1.0 and 5.0 μg/mL, the mean recoveries of analyte on the MIP were higher than 90% with relative standard deviation <10%, and significant differences between imprinted and non-imprinted materials were observed. The MIP selectivity was evaluated by checking 11 drugs with similar and different molecular structures to that of RAC. The characteristics of three-dimensional cavities and hydrogen bond interaction were regarded as the main factors that dominated the retention of RAC on the MISPE cartridge.     

Guiding Molecularly Imprinted Polymer Design by Pharmacophore Modeling

Molecularly imprinted polymers (MIP) combine the selectivity of immunoaffinity chromatography with the robustness of common solid-phase extraction in what is referred to as molecularly imprinted solid-phase extraction (MISPE). This contribution shows how MIP design may be guided by pharmacophore modeling for the example of citrinin, which is an emerging mycotoxin from cereals. The obtained pharmacophore model allowed searching public databases for a set of citrinin-mimicking molecular surrogates. Imprinted and non-imprinted polymers were subsequently obtained through bulk and core-shell polymerization in the presence of these surrogates. Evaluation of their binding ability for citrinin and structurally related ochratoxin A revealed a promising MIP derived from rhodizonic acid. A protocol for MISPE of citrinin from cereals was subsequently developed and compared to immunoaffinity chromatography with respect to clean-up efficiency and recovery.     

Synthesis and application of molecularly imprinted polymer on selective solid-phase extraction for the determination of monosulfuron residue in soil

A novel sample clean-up procedure using molecularly imprinted polymer as the solid-phase extraction material for the determination of monosulfuron residue in soil samples has been developed. The molecularly imprinted polymer (MIP) was synthesized by non-covalent method with monosulfuron as the template. The selectivity and affinity of the MIP was evaluated by equilibrium adsorption and HPLC experiments, which demonstrated that the MIP has specific affinity for the template. The template-MIP interaction was studied by investigating the influence of different mobile phases on the retention of the template, which provided basic knowledge for the selection of the washing and elution solutions in the molecularly imprinted solid-phase extraction (MISPE) process. The study indicated that polar organic solvents with hydrogen bonding abilities have stronger eluting strength for the monosulfuron. After the MISPE procedure, a clean baseline was obtained in the HPLC quantification analysis. The recoveries of the method using the combination of MISPE and HPLC were above 93% and the R.S.D. was less than 3.2% in the soil sample determinations. Low detection limit (0.08 microg g(-1), when defined as 3 times of the noise) was also obtained in the method evaluation study.     

Analysis of triclosan and triclocarban in soil and biosolids using molecularly imprinted solid phase extraction coupled with HPLC-UV

A molecularly imprinted polymer (MIP) able to selectively bind triclosan (TCS) and triclocarban (TCC), commonly used antibacterial agents in many consumer products, was prepared using noncovalent molecular imprinting methods. The prepared MIP was evaluated as a selective sorbent in SPE for sample cleanup before HPLC-UV analysis of TCS and TCC in soil and biosolid samples. The MIP was also compared with commercially available C18 SPE sorbent. The molecularly imprinted SPE (MISPE) developed in this study was more efficient than C18 SPE for the cleanup of extracts of soil and biosolid samples prior to the analysis of TCC and TCS using HPLC-UV. The LOQ values for both TCC and TCS in the soil samples were determined to be 40 microg/kg; in the biosolid samples, the LOQ values were 100 and 300 microg/kg for TCC and TCS, respectively. Compared to C18 SPE, using MISPE for sample cleanup may result in a significant reduction of analytical cost, because one MIP can be reused up to 35 times and HPLC-UV instead of HPLC/MS can be used for instrumental analysis following sample cleanup by MISPE.     

Macromolecular Crowding Agents‐Assisted Imprinted Polymers For Analysis Of Glycocholic Acid In Human Plasma And Urine

Glycocholic acid (GCA) is a newly identified biomarker for hepatocellular carcinoma (HCC) patients. In this study, a method based on macromolecular crowding strategy has been applied for preparation of a molecularly imprinted polymer (MIP), which possesses high adsorption capacity for GCA. Polymethyl methacrylate was used as a macromolecular crowding agent, N‐(3‐aminopropyl)‐methacrylamide hydrochloride as a functional monomer and ethylene dimethacrylate as a cross‐linker. The morphology and binding characteristics of MIP were assessed by scanning electron microscopy and absorption experiments. The MIP was used as an adsorbent material to separate GCA, and the molecularly imprinted solid‐phase extraction (MISPE) was carefully optimized. The MISPE combined with high‐performance liquid chromatographic analysis was successfully used to determine the GCA in plasma and urine samples. When spiked levels ranged from 0.2 to 20 μmol L^?1, the recoveries were between 94.3 and 100.5%. As a proof of principle, this proposed method has been validated on a small subset of HCC patients (n = 10) and healthy volunteers (n = 10). The average GCA concentrations of HCC patients in plasma and urine were about 25 and 2.8 times than that of healthy volunteers. Copyright © 2016 John Wiley & Sons, Ltd.     

Determination of a flame retardant hydrolysis product in human urine by SPE and LC–MS. Comparison of molecularly imprinted solid-phase extraction with a mixed-mode anion exchanger

Diphenyl phosphate is a hydrolysis product and possible metabolite of the flame retardant and plasticiser additive triphenyl phosphate. A molecularly imprinted polymer solid-phase extraction (MISPE) method for extracting diphenyl phosphate from aqueous solutions has been developed and compared with SPE using a commercially available mixed-mode anion exchanger. The imprinted polymer was prepared using 2-vinylpyridine (2-Vpy) as the functional monomer, ethylene glycol dimethacrylate (EGDMA) as the cross-linker, and a structural analogue of the analyte as the template molecule. The imprinted polymer was evaluated for use as a SPE sorbent, in tests with both aqueous standards and spiked urine samples, by comparing recovery and breakthrough data obtained using the imprinted form of the polymer and a non-imprinted form (NIP). Extraction from aqueous solutions resulted in more than 80% recovery. Adsorption by the molecularly imprinted polymer (MIP) was non-selective , but selectivity was achieved by selective desorption in the wash steps. Diphenyl phosphate could also be selectively extracted from urine samples, although the urine matrix reduced the capacity of the MISPE cartridges. Recoveries from urine extraction were higher than 70%. It was important to control pH during sample loading. The MISPE method was found to yield a less complex LC–ESI–MS chromatogram of the urine extracts compared with the mixed-mode anion-exchanger method. An LC–ESI–MS method using a Hypercarb LC column with a graphitised carbon stationary phase was also evaluated for organophosphate diesters. LC–ESI–MS using negative-ion detection in selected ion monitoring (SIM) mode was shown to be linear for diphenyl phosphate in the range 0.08–20 ng L^–1.     

Synthesis and characterization of a novel molecularly imprinted polymer for simultaneous extraction and determination of water-soluble and fat-soluble synthetic colorants in chilli products by solid phase extraction and high performance liquid chromatography

A sorbent was synthesized and investigated for molecularly imprinted solid phase extraction (MISPE). Molecularly imprinted polymers (MIP) were synthesized via precipitation polymerization procedure, where 4-vinyl pyridine (4-VP) was used as functional monomer and ethylene glycol dimethacrylate (EDMA) as cross-linking agent. The imprinting effect of the MISPE was evaluated by elution experiments. The resulting MISPE showed high extraction selectivity to water-soluble and fat-soluble synthetic colorants. The determination of multi-residue for three kinds of water-soluble and six kinds of fat-soluble synthetic colorants in chilli products was also investigated by HPLC coupled with MISPE. The mean recoveries calculated by solvent calibration curve for water-soluble and fat-soluble synthetic colorants were from 72.1% to 95.6% for chilli spice and 72.1% to 92.3% for chilli powder. The decision limit (CCα) and the detection capability (CCβ) obtained for water-soluble and fat-soluble synthetic colorants were in the range of 1.2–1.6 and 1.9–2.4 μg kg⁻¹ in chilli spice and chilli powder. The resulting MISPE was successfully used off-line for the determination of nine kinds of synthetic colorants in chilli products.     

Synthesis and characterization of molecularly imprinted polymers for selective solid-phase extraction of pseudoephedrine

Molecular imprinted solid-phase extraction (MISPE) is a well known technique for the selective extraction and pre-concentration of analytes, are present at low levels in chemically complex materials. Herein, water-soluble, molecularly imprinted polymers (MIP) were prepared for solid-phase extraction of pseudoephedrine hydrochloride (PSE), which was monitored at 256 nm by the UV spectroscopy. MISPE conditions were optimized to allow the selective and determination of PSE in aqueous samples and composite materials, such as biological fluids and human urine. MIP was prepared by precipitation polymerization method, using methacrylic acid as a functional monomer and ethylene glycol dimethacrylate as a cross-linking agent in either acetonitrile or chloroform. The results suggest that the obtained MISPE exhibits high affinity for PSE, and the imprinted polymer demonstrates much higher efficiency than a non-imprinted polymer (NIP). The imprinting-induced extraction was confirmed by the determination of recovery values for NIP (4%) and MIP (80%) polymers, respectively. The binding capacity of the MIP for PSE was found of 47.6 mg g⁻¹.     

Preparation and characterization of a lamotrigine imprinted polymer and its application for drug assay in human serum

A molecularly imprinted polymer (MIP) against lamotrigine (LTG) was prepared, characterized, and its recognition properties were compared with a blank nonimprinted polymer (NIP). Two classes of binding sites were found in the MIP--high affinity (K(D) = 16.2 microM) and low affinity (K(D) = 161.3 microM). Selectivity of the synthesized MIP was examined using compounds with similar structures or therapeutic uses to LTG. In compounds which had structural similarity to LTG, the presence of amine groups appeared to affect binding to the MIP, however overall shape of the molecule was also important. Under the optimal conditions developed, other anticonvulsant drugs tested did not bind the MIP. A molecularly imprinted SPE (MISPE) procedure was developed which had a recovery of 84-89%, interday variation of less than 3.4% and intraday variation of less than 2.8%. The MISPE procedure was compared with a routine liquid-liquid extraction (LLE) procedure used for the HPLC determination of LTG in serum from patients. The data indicated that the MIP synthesized showed both good selectivity and high affinity for LTG and could be used for the extraction of the drug from serum samples or as the receptor layer for an LTG selective biosensor.     

Molecularly imprinted polymers: An analytical tool for the determination of benzimidazole compounds in water samples

Molecularly imprinted polymers (MIPs) for benzimidazole compounds have been synthesized by precipitation polymerization using thiabendazole (TBZ) as template, methacrylic acid as functional monomer, ethyleneglycol dimethacrylate (EDMA) and divinylbenzene (DVB) as cross-linkers and a mixture of acetonitrile and toluene as porogen. The experiments carried out by molecularly imprinted solid phase extraction (MISPE) in cartridges demonstrated the imprint effect in both imprinted polymers. MIP–DVB enabled a much higher breakthrough volume than MIP–EDMA, and thus was selected for further experiments. The ability of this MIP for the selective recognition of other benzimidazole compounds (albendazole, benomyl, carbendazim, fenbendazole, flubendazole and fuberidazole) was evaluated. The obtained results revealed the high selectivity of the imprinted polymer towards all the selected benzimidazole compounds.An off-line analytical methodology based on a MISPE procedure has been developed for the determination of benzimidazole compounds in tap, river and well water samples at concentration levels below the legislated maximum concentration levels (MCLs) with quantitative recoveries. Additionally, an on-line preconcentration procedure based on the use of a molecularly imprinted polymer as selective stationary phase in HPLC is proposed as a fast screening method for the evaluation of the presence of benzimidazole compounds in water samples.     

Clean up of phenylurea herbicides in plant sample extracts using molecularly imprinted polymers

Two different molecularly imprinted polymers (MIPs) were prepared by precipitation polymerization using linuron or isoproturon (phenylurea herbicides) as templates and trifluormethacrylic acid as functional monomer. These materials were used as selective sorbents in the development of molecularly imprinted solid-phase extraction (MISPE) procedures for the determination of several phenylurea herbicides (fenuron, metoxuron, chlortoluron, isoproturon, metobromuron, and linuron) in plant samples extracts. The MISPE procedures were fully optimized and applied to the clean up of selected phenylurea herbicides in carrot, potato, corn, and pea sample extracts and finally determined by HPLC-UV at 244 nm. Although a high degree of clean up was obtained, a decrease of the MIP recognition capabilities was observed in subsequent runs. Thus, a previous clean up protocol based on the use of a non-imprinted polymer was used to prevent the loss of MIP performance and to ease the removal of interferences. Following this procedure, namely two-step MISPE, matrix compounds were almost completely removed by the non-imprinted polymer retaining the ability of MIPs to selectively rebind target analytes unaltered. The developed MISPE procedures allowed the screening of phenylurea herbicides in plant samples at concentration levels required by established European maximum residue limits.     

A selective molecularly imprinted polymer-solid phase extraction for the determination of fenitrothion in tomatoes

A new and selective sorbent for molecularly imprinted solid-phase extraction (MISPE) was developed and applied for the determination of residues of fenitrothion (FNT) in tomatoes, using HPLC coupled to photodiode array detection (HPLC-DAD). Using FNT as the template molecule, methacrylic acid as the functional monomer, ethylene glycol dimethacrylate as the cross-linker, toluene as the porogenic solvent, and bulk polymerization as the synthetic method, a molecularly imprinted polymer (MIP) was synthesized. In order to choose the medium which promotes the best molecular recognition of FNT by the MIP, the adsorption of FNT by the MIP was studied in different media containing acetonitrile and toluene. Besides FNT, three structurally related compounds were used to evaluate the selectivity of the FNT-molecularly imprinted polymer. The MIP exhibited the highest selective rebinding to FNT. The method developed was validated, using fortified blank tomato samples. The extraction efficiency was 96%. The limits of detection and quantitation were 0.050 and 0.130 μg g⁻¹, respectively. The intra-day precision was 5.9% and the inter-day precision 8.1%. The accuracy was higher than 89% for a concentration level around the maximum residue limit of 0.5 μg g⁻¹.     

Selective solid-phase extraction using molecularly imprinted polymer for the analysis of polar organophosphorus pesticides in water and soil samples

An analytical methodology for the analysis of four polar organophophorus pesticides (monocrotophos, mevinphos, phosphamidon, omethoate) in water and soil samples incorporating a molecularly imprinted solid-phase extraction (MISPE) process using a monocrotophos-imprinted polymer was developed. Binding study demonstrated that the polymer showed excellent affinity and high selectivity to monocrotophos. The MISPE procedure including the clean-up step to remove any interferences was optimized. The accuracy and selectivity of the MISPE process developed were verified using a non-imprinted (blank) polymer and a classical ENVI-18 cartridge as the SPE matrix during control experiments. The use of MISPE improved the accuracy and precision of the GC method and lowered the limit of detection. The recoveries of four polar organophosphorus pesticides (OPPs) extracted from 1 L of river water at a 100 ng/L spike level were in the range of 77.5-99.1%. The recoveries of organophosphorus pesticides extracted from a 5-g soil sample at the 100 microg/kg level were in the range of 79.3-93.5%. The limit of detection varied from 10 to 32 ng/L in water and from 12 to 34 microg/kg in soil samples. The molecularly imprinted polymer (MIP) enabled the selective extraction of four organophosphorus pesticides successfully from water and soil samples, demonstrating the potential of molecularly imprinted solid-phase extraction for rapid, selective, and cost-effective sample pretreatment.