Evaluation of a novel silica-supported sol–gel sorbent prepared by a surface molecular imprinting technique for the selective separation of estazolam from human plasma

A molecular imprinting polymer (MIP) based on surface modification of silica gel was prepared via the sol–gel process with 3-aminopropyltriethoxysilane and phenyltrimethoxysilane as functional monomers, and estazolam as the template. The imprinted silica sorbent was characterized by Fourier Transform Infrared Spectroscopy, surface elemental analysis, and scanning electron microscopy (SEM). An MIP of agglomerated nano-particles with multi-pores was grafted onto the surface of the silica gel after hydrolytic condensation of the siloxane. The imprinted silica sorbent was used for solid phase extraction (SPE). Using water as loading solvent, the extraction efficiency for estazolam was higher compared to the use of an organic solvent. The imprinted silica sorbent was selective not only for the template, but also for the analogue. Compared to C₁₈-SPE and liquid–liquid extraction, the MIP-SPE was the most feasible technique for extraction of estazolam from human plasma; up to 98.7?±?1.2% recovery was achieved.     

A novel sol-gel-material prepared by a surface imprinting technique for the selective solid-phase extraction of bisphenol A

A novel and simple imprinted amino-functionalized silica gel material was synthesized by combining a surface molecular imprinting technique with a sol-gel process on the supporter of activated silica gel for solid-phase extraction-high performance liquid chromatography (SPE-HPLC) determination of bisphenol A (BPA). Non-imprinted silica sorbent was synthesized without the addition of BPA using the same procedure as that of BPA-imprinted silica sorbent. The BPA-imprinted silica sorbent and non-imprinted silica sorbent were characterized by FT-IR and the static adsorption experiments. The prepared BPA-imprinted silica sorbent showed high adsorption capacity, significant selectivity and good site accessibility for BPA. The maximum static adsorption capacity of the BPA-imprinted and non-imprinted silica sorbent for BPA was 68.9 and 34.0 mg g⁻¹, respectively. The relatively selective factor value of this BPA-imprinted silica sorbent was 4.5. Furthermore, the difference of the retention characteristics of BPA on the C₈ SPE column and BPA-imprinted silica SPE (MIP-SPE) was compared. The MIP-SPE-HPLC method showed higher selectivity to BPA than the traditional SPE-HPLC method. At last, the BPA-imprinted polymers were used as the sorbent in solid-phase extraction to determine BPA in water samples with satisfactory recovery higher than 99% (R.S.D. 3.7%).     

Novel surface molecularly imprinted material modified multi-walled carbon nanotubes as solid-phase extraction sorbent for selective extraction gallium ion from fly ash

A new gallium (Ga(III)) ion-imprinted multi-walled carbon nanotubes (CNTs) composite sorbent was synthesized by a surface imprinting technique. The Ga(III) ion-imprinted/multi-walled carbon nanotubes (Ga(III)-imprinted/CNTs) sorbent was characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), nitrogen adsorption experiment, static adsorption experiment, and solid-phase extraction (SPE) experiment. The effects of sample volume, sample pH, washing and elution conditions on the extraction of Ga(III) ion from real sample were studied in detail. The imprinted sorbent offered a fast kinetics for the adsorption of Ga(III). The maximum static adsorption capacity of the imprinted sorbent towards was 58.8 μmol g⁻¹. The largest selectivity coefficient for Ga(III) in the presence of Al(III) was over 57.3. Compared with non-imprinted sorbent, the imprinted sorbent showed good imprinting effect for Ga(III) ion, the imprinting factor (α) was 2.6, the selectivity factor (β) was 2.4 and 2.9 for Al(III) and Zn(II), respectively. The developed imprinted SPE method was applied successfully to the detection of trace Ga(III) ion in fly ash samples with satisfactory results.     

SPE of Tanshinones from Salvia miltiorrhiza Bunge by using Imprinted Functionalized Ionic Liquid-Modified Silica

Ionic liquid-modified silica, with functional groups based on imidazole as the cation, was obtained. A molecular imprinting technique was introduced to form the order of functional groups. The selectivity of the obtained ionic liquid-modified silica was successfully used as a special imprinted sorbent in the solid-phase extraction to isolate cryptotanshinone, tanshinone I and tanshinone IIA from Salvia miltiorrhiza Bunge. Several washing and elution solvents with different polarities were evaluated. The ionic liquid-modified silica as the sorbent exhibited a higher selectivity than blank ionic liquid-modified silica, traditional silica and C₁₈ cartridges. A quantitative analysis was conducted by liquid chromatography with a C₁₈ column and methanol/water (75:25, v/v, containing 0.5% acetic acid) as the mobile phase. A good linearity was obtained from 0.5 × 10^?4 to 0.1 mg mL^?1 (r ²  > 0.99) with relative standard deviations that were less than 4.6%.     

Properties and Application of a Chelating Sorbent Prepared by Modification of LiChroprep-NH<Subscript>2</Subscript> with Calcon

A new chelating sorbent for metal ions was prepared by modification of chemically modified silica – LiChroprep-NH₂ with Calcon. The molecular mechanism of binding this reagent to the surface of the applied carrier is presented. The properties of this sorbent were compared to analogous sorbents with a plain silica carrier and chemically modified silicas – LiChroprep-RP containing Calcon. The advantages of the new sorbent compared to the silica and LiChroprep-RP chelating sorbents are demonstrated. The sorbent obtained was applied as stationary phase in solid-phase extraction (SPE) for separations of some chosen mixtures of metal ions and for additional purification of aqueous solutions of salts of alkali metals from trace amounts of heavy metals. The multiple use of the sorbent based on LiChroprep-NH₂ in sorption-desorption processes of metal ions without deterioration of its sorption capacity is demonstrated.     

Preparation and evaluation of an ion imprinted sol–gel material for selective solid-phase extraction of Ni(II)

An ion imprinted silica sorbent was prepared using a sol–gel process for selective extraction of Ni(II) ions from water samples. Bis(dibenzoylmethanto)nickel(II) complex was used as template; phenyltrimethoxysilane and 3-aminopropyltriethoxysilane as functional monomers and tetraethylorthosilicate as reticulating agent. The material was packed in solid-phase extraction (SPE) column. The effect of sampling volume, elution conditions, sample pH and sample flow rate on the extraction of Ni ions from water samples were studied. The relative selectivity coefficients of imprinted sorbent for Ni(II)/Co(II), Ni(II)/Cu(II) and Ni(II)/Cd(II) were 23.7, 30.3 and 24.4, times greater than non-imprinted sorbent, respectively. The relative standard deviation of the eight replicate determinations of Ni(II) was 4.2%. The detection limit was 0.9 µg L^?1 using flame atomic absorption spectrometry. The developed method was successfully applied to the determination of trace nickel in water samples.     

Preparation and Characteristics of Esculin‐Imprinted Polymers

Four molecularly imprinted polymers (MIPs) were prepared in MeOH with esculin (=6,7‐dihydroxycoumarin 6‐(β‐D ‐glucopyranoside)=6‐(β‐D ‐glucopyranosyloxy)‐7‐hydroxy‐2H‐1‐benzopyran‐2‐one) as the imprinted molecule, methacrylic acid (=2‐methylprop‐2‐enoic acid; MAA), acrylamide (=prop‐2‐enamide; AM), 4‐vinylpyridine (=4‐ethenylpyridine; 4‐VP), or 2‐vinylpyridine (=2‐ethenylpyridine; 2‐VP) as the functional monomer, respectively, as well as ethylene glycol dimethacrylate (=2‐methylprop‐2‐enoic acid ethane‐1,2‐diyl ester; EGDMA) as the cross‐linking agent. The interaction between the template and the functional monomers was investigated by fluorescence and UV spectrophotometry, respectively, which revealed the presence of esculin/monomer complexes in the stoichiometric ratio 1 : 2 in the pre‐polymerization mixture. The resultant polymers were studied in equilibrium binding experiments to evaluate the recognition ability and the binding capacity towards esculin. The results showed that MIP₁, prepared with MAA as the functional monomer, exhibited advantageous characteristics of high binding capacity, optimal imprinting effect, and good selectivity towards esculin. The Scatchard analysis indicated that there are two types of binding sites in MIP₁, and its binding parameters including the apparent maximum numbers of binding sites and the dissociation constants were calculated. Finally, by packing an SPE column (SPE=solid‐phase extraction) with MIP₁, the esculin was separated and enriched successfully by this sorbent from samples of Cortex fraxini, and the average recovery was up to 74.7%.     

Preparation and adsorption properties of glucose molecularly imprinted polymers in hydrous solution for effective determination of glucose in fruits by MISPE–HPLC

In this paper, a kind of surface molecular imprinting polymers in hydrous solution, with glucose selectively recognition, was successfully synthesized by surface molecular imprinting method, using glucose (Glu) as template molecule, acrylamide as functional monomers, N,N′-methylenebisacrylamide as the cross-linking agent, ammonium peroxydisulfate as the initiator, activated silica gel (SiO₂@NH₂) as support particles. The influences of cross-linker, initiator as well as support particles amount on the adsorption capacity of Glu-MIPs were performed by single-factor experiments. The optimum conditions were 100 mg of cross-linker, 25 mg of initiator and 1 g of SiO₂@NH₂. The adsorption and thermodynamics research revealed that the adsorption of MIPs was fitted to Langmuir, maximum imprinting factor of 2.49 and maximum absorption capacity of 50.06 mg/g. Furthermore, a procedure of extraction of glucose from real fruits samples using the Glu-MIPs as solid-phase extraction adsorbent was developed to apply in analytical techniques.     

Imprinted functionalized silica sol-gel for solid-phase extraction of triazolamin

A triazolam-imprinted silica microsphere was prepared by combining a surface molecular-imprinting technique with the sol-gel process. The results illustrate that the triazolam-imprinted silica microspheres provided using γ-aminopropyltriethoxysilane and phenyltrimethoxysilane as monomers exhibited higher selectivity than those provided from γ-aminopropyltriethoxysilane and methyltriethoxysilane. In addition, the optimum affinity occurred when the molar ratio of γ-aminopropyltriethoxysilane, phenyltrimethoxysilane, and the template molecule was 4.2:4.7:0.6. Retention factor (k) and imprinting factor (IF) of triazolam on the imprinted and non-imprinted silica microsphere columns were characterized using high performance liquid chromatography (HPLC) with different mobile phases including methanol, acetonitrile, and water solutions. The molecular selectivity of the imprinted silica microspheres was also evaluated for triazolam and its analogue compounds in various mobile phases. The better results indicated that k and IF of triazolam on the imprinted silica microsphere column were 2.1 and 35, respectively, when using methanol/water (1/1, v/v) as the mobile phase. Finally, the imprinted silica was applied as a sorbent in solid-phase extraction (SPE), to selectively extract triazolam and its metabolite, α-hydroxytriazolam, from human urine samples. The limits of detection (LOD) for triazolam and α-hydroxytriazolam in urine samples were 30 ± 0.21 ng mL⁻¹ and 33 ± 0.26 ng mL⁻¹, respectively.     

Selective extraction of clonazepam from human plasma and urine samples by molecularly imprinted polymeric beads

A molecularly imprinted polymer (MIP) based on free‐radical polymerization was prepared with 1‐(N,N‐biscarboxymethyl)amino‐3‐allylglycerol and N,N‐dimethylacrylamide as functional monomers, N,N‐methylene diacrylamide as the cross‐linker, copper ion‐clonazepam as the template and 2,2‐azobis(2‐methylbutyronitrile) as the initiator. The imprinted polymer was characterized by Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis, and SEM. The MIP of agglomerated microparticles with multipores was used for SPE. The imprinted polymer sorbent was selective for clonazepam. The optimum pH and sorption capacity were 5 and 0.18 mg/g at 20°C, respectively. The profile of the drug uptake by the sorbent reflects good accessibility of the active sites in the imprinted polymer sorbent. The MIP‐SPE was the most feasible technique for the extraction of clonazepam with a high recovery from human plasma and urine samples.     

Solid-phase extraction of iron(III) with an ion-imprinted functionalized silica gel sorbent prepared by a surface imprinting technique

A new Fe(III)-imprinted amino-functionalized silica gel sorbent was prepared by a surface imprinting technique for selective solid-phase extraction (SPE) of Fe(III) prior to its determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Compared with non-imprinted polymer particles, the ion-imprinted polymers (IIPs) had higher selectivity and adsorption capacity for Fe(III). The maximum static adsorption capacity of the ion-imprinted and non-imprinted sorbent for Fe(III) was 25.21 and 5.10 mg g⁻¹, respectively. The largest selectivity coefficient of the Fe(III)-imprinted sorbent for Fe(III) in the presence of Cr(III) was over 450. The relatively selective factor (α_r) values of Fe(III)/Cr(III) were 49.9 and 42.4, which were greater than 1. The distribution ratio (D) values of Fe(III)-imprinted polymers for Fe(III) were greatly larger than that for Cr(III). The detection limit (3σ) was 0.34 μg L⁻¹. The relative standard deviation of the method was 1.50% for eight replicate determinations. The method was validated by analyzing two certified reference materials (GBW 08301 and GBW 08303), the results obtained is in good agreement with standard values. The developed method was also successfully applied to the determination of trace iron in plants and water samples with satisfactory results.     

SPE for the simultaneous determination of various isothiocyanates

Several SPE sorbents were investigated for the extraction of a group of chemically diverse isothiocyanates (ITCs). They included bonded silica, carbon‐based, and polymer‐based sorbents with various functional groups. Results showed large differences in the ability of these sorbents to simultaneously extract ITCs from standard solutions. Recovery rates were on average the highest with divinylbenzene (DVB) based polymeric sorbents, especially with a DVB/N‐vinylpyrrolidone copolymer that had recovery rates ranging between 86.7 and 95.6%. These sorbents achieved the most balanced extraction efficiency between aliphatic and aromatic, polar, and nonpolar ITCs. With graphitized carbon, C₁₈‐bonded silica, and amide‐containing sorbent, recovery levels were higher for the two least polar aromatic ITCs (benzyl ITC and phenylethyl ITC), whereas for the polar aliphatic ITCs levels were the lowest. The least retained one, was methyl ITC that is the most polar with recoveries between 0 and 31.5%. The presence of amide groups, especially in a polyamide sorbent, appeared to be particularly unsuitable for the extraction of aliphatic ITCs. A copolymer made up of DVB and N‐vinylpyrrolidone was therefore shown to be the most suited for the extraction of both aliphatic and aromatic ITCs.     

Synthetic approaches to parabens molecularly imprinted polymers and their applications to the solid-phase extraction of river water samples

In this paper we describe the synthesis, characterisation and use of two distinct molecularly imprinted polymers (MIPs) prepared using esters of p-hydroxybenzoic acid (parabens) as templates: one MIP was synthesised by precipitation polymerisation using a semi-covalent molecularly imprinting strategy with methyl paraben as the template/target (MIP 1); the second MIP was prepared in monolithic form through a conventional non-covalent molecular imprinting strategy, with butyl paraben as the template (MIP 2). MIP 1 recognized methyl paraben, showed cross-selectivity for other parabens analytes used in the study and higher affinity towards these compounds than did a non-imprinted control polymer. Similarly, MIP 2 demonstrated higher affinity towards paraben analytes than a non-imprinted control polymer.For the analysis of environmental water samples, a solid-phase extraction (SPE) protocol was developed using MIP 2 as sorbent, and results were compared to a SPE using a commercial sorbent (Oasis HLB). With MIP 2 as sorbent and butyl paraben as target, when percolating 500 mL of river water spiked at 1 μg L⁻¹ through the SPE cartridge, and using 1 mL of isopropanol as cleaning solvent, a higher recovery of butyl 4-hydroxybenzoate (butyl paraben) and a cleaner chromatogram where achievable when using the MIP compared to the commercial sorbent.     

Extraction and preconcentration of ultra trace amounts of beryllium from aqueous samples by nanometer mesoporous silica functionalized by 2,4-dihydroxybenzaldehyde prior to ICP OES determination

A new functionalized nanometer mesoporous silica (MCM-41) using 2,4-dihydroxybenzaldehyde (4-OHsal) was applied as an effective sorbent for solid phase extraction (SPE) of beryllium ions from aqueous solution followed by inductively coupled plasma optical emission spectrometric detection (ICP OES). The influences of some analytical parameters on the quantitative recoveries of the analyte ion were investigated in batch method. In order to perform the batch mode of SPE, known amount of sorbent was added to a test tube containing sample solution buffered at pH 7.2. After manual shaking and centrifugation the aqueous phase was decanted and beryllium was desorbed by adding 1.0 mL of 1.0 mol L^?1 HNO₃ to the sedimented sorbent. The sorbent was separated by centrifugation and the concentration of beryllium in the supernatant was determined by ICP OES. The maximum sorption capacity of the modified MCM-41 was found to be 34 mg g^?1. The sorbent exhibited good stability, reusability and fast rate of equilibrium for sorption/desorption of beryllium ions. The present method was used for preconcentration and determination of beryllium for water samples. Under optimal conditions, the limit of detection (LOD) obtained was 0.3 ng L^?1. The accuracy of the procedure was evaluated by analysis of the certified reference material (NIST 1640).     

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 × 10⁵ mL μmol⁻¹ and 16.4 μmol 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.     

Poly(methyltetradecylsiloxane) immobilized onto silica for extraction of multiclass pesticides from surface waters

A new material based on poly(methyltetradecylsiloxane) (PMTDS) thermally immobilized onto a silica support has been tested as a sorbent for the solid-phase extraction (SPE) from water of several pesticides used in soybean cultivation. The SPE methodology was developed and validated for six of these pesticides (imazethapyr, imazaquin, metsulfuron-methyl, bentazone, chlorimuron-ethyl and tebuconazole) according to the International Conference on Harmonization directives and the results were compared with those obtained with a commercial C18 SPE cartridge. The PMTDS-based sorbent gives results similar to the commercial sorbent with recoveries and precisions in agreement with directives for residue analysis. The quantification limits, after concentration, of all the pesticides evaluated were 1.0 μg L⁻¹, below the levels imposed by the principal regulatory agencies. The PMTDS-based sorbent preparation is fast, easy and reproducible and the cartridges are less expensive than similar commercial SPE materials.     

Development of a Solid‐Phase Extraction‐Enzyme‐Linked Immunosorbent Assay Method with a New Sorbent of Multiwall Carbon Nanotube for the Determination of Estrone in Water

Abstract

A sensitive solid‐phase extraction‐enzyme‐linked immunosorbent assay (SPE‐ELISA) method was developed to analyze the estrone in environmental water. A new SPE sorbent of the multiwall carbon nanotube was tested and proved to have similar adsorbability for estrone comparing to the commercial C₁₈ SPE. A specific polyclonal antibody for estrone (A‐E1) and a broad‐spectrum antibody for estrone, estradiol and estriol (A‐E2) were produced. For A‐E1, the limit detection of estrone was 0.04 µg/l and for A‐E2 were 0.07, 0.04 and 0.2 µg/l of estrone, estradiol and estriol, respectively. Different river water samples were analyzed by ELISA and HPLC method.     

Ni(II) ion-imprinted solid-phase extraction and preconcentration in aqueous solutions by packed-bed columns

Solid-phase extraction (SPE) columns packed with materials based on molecularly imprinted polymers (MIPs) were used to develop selective separation and preconcentration for Ni(II) ion from aqueous solutions. SPE is more rapid, simple and economical method than the traditional liquid-liquid extraction. MIPs were used as column sorbent to increase the grade of selectivity in SPE columns. In this study, we have developed a polymer obtained by imprinting with Ni(II) ion as a ion-imprinted SPE sorbent. For this purpose, NI(II)-methacryloylhistidinedihydrate (MAH/Ni(II)) complex monomer was synthesized and polymerized with cross-linking ethyleneglycoldimethacrylate to obtain [poly(EGDMA-MAH/Ni(II))]. Then, Ni(II) ions were removed from the polymer getting Ni(II) ion-imprinted sorbent. The MIP-SPE preconcentration procedure showed a linear calibration curve within concentration range from 0.3 to 25 ng/ml and the detection limit was 0.3 ng/ml (3 s) for flame atomic absorption spectrometry (FAAS). Ni(II) ion-imprinted microbeads can be used several times without considerable loss of adsorption capacity. When the adsorption capacity of nickel imprinted microbeads were compared with non-imprinted microbeads, nickel imprinted microbeads have higher adsorption capacity. The K_d (distribution coefficient) values for the Ni(II)-imprinted microbeads show increase in K_d for Ni(II) with respect to both K_d values of Zn(II), Cu(II) and Co(II) ions and non-imprinted polymer. During that time K_d decreases for Zn(II), Cu(II) and Co(II) ions and the k′ (relative selectivity coefficient) values which are greater than 1 for imprinted microbeads of Ni(II)/Cu(II), Ni(II)/Zn(II) and Ni(II)/Co(II) are 57.3, 53.9, and 17.3, respectively. Determination of Ni(II) ion in sea water showed that the interfering matrix had been almost removed during preconcentration. The column was good enough for Ni determination in matrixes containing similar ionic radii ions such as Cu(II), Zn(II) and Co(II).     

Molecularly imprinted solid-phase extraction of naphthalene sulfonates from water

A new polymeric sorbent synthesised by exploiting molecular imprinting technology has been used to selectively extract naphthalene sulfonates (NSs) directly from aqueous samples. In the non-covalent molecular imprinting approach used to prepare this polymer, 1-naphthalene sulfonic acid (1-NS) and 4-vinylpyridine (4-VP) were used as a template molecule and functional monomer, respectively, and both dissolved in a mixture of methanol/water (4:1) as porogen together with the cross-linker ethylene glycol dimethacrylate. The new non-covalent molecularly imprinted polymer (MIP) prepared in aqueous environment was used as a sorbent in solid-phase extraction (SPE) to selectively extract a group of naphthalene mono- and disulfonates. When one litre of a standard aqueous solution, which contained a mixture of eight NSs, was percolated through the SPE cartridge, all the NSs were retained on the MIP because of the cross-reactivity of the polymer. Recoveries were higher than 80% for all the compounds even after a clean-up step with methanol (MeOH). The MIP was also used to analyse water from the Ebro river.     

Stripping voltammetric analysis of organophosphate pesticides based on solid-phase extraction at zirconia nanoparticles modified electrode

A sensitive electrochemical stripping voltammetric method for analyzing organophosphate (OP) compounds was developed based on solid-phase extraction (SPE) at zirconia (ZrO₂) nanoparticles modified electrode. ZrO₂ nanoparticles were proved as a new sorbent for SPE of OP pesticides. Because of the strong affinity of ZrO₂ for the phosphoric group, nitroaromatic OPs can strongly bind to the ZrO₂ nanoparticle surface. The combination of SPE with square-wave voltammetry (SWV) provided a fast, sensitive, and selective electrochemical method for nitroaromatic OP compounds using methyl parathion (MP) as a model. The stripping response was highly linear over the MP range of 0.003–2.0 μg/mL, with a detection limit of 0.001 μg/mL. The fast extraction ability of ZrO₂ nanoparticles makes it promising sorbent for various solid-phase extractions.