This review describes the recent advances from the past five years concerning the development and applications of molecularly imprinted membranes (MIMs) in the field of sample treatment and ...separation processes. After a short introduction, where the importance of these materials is highlighted, a description of key aspects of membrane separation followed by the strategies of preparation of these materials is described. The review continues with several analytical applications of these MIMs for sample preparation as well as for separation purposes covering pharmaceutical, food, and environmental areas. Finally, a discussion focused on possible future directions of these materials in extraction and separation field is also given.
A selective magnetic molecularly imprinted polymer (MMIP) was synthetized with 4-chloro-2-methylphenoxyacetic acid as template and 4-vinylpiridine as monomer in presence of vinylized magnetite ...nanoparticles. Scanning electron microscopy, nitrogen adsorption-desorption isotherms, Fourier transform infrared spectrometry and vibrating sample magnetometry were applied to characterize the resulting material. The synthesized MMIP was applied as sorbent in magnetic molecularly imprinted solid-phase extraction (MMISPE) for selective extraction of a mixture of the five herbicides 4-chloro-2-methylphenoxyacetic acid (MCPA), 4-(4-chloro-2-methylphenoxy)butyric acid (MCPB), mecoprop (MCPP), fenoxaprop (FEN) and haloxyfop (HAL). Several parameters affecting the extraction conditions were optimized to achieve the best extraction performance. The best MMISPE combined with HPLC-DAD gave detection and quantification limits between 0.33 and 0.71 μg L−1 and 1.1–2.4 μg L−1, respectively, were obtained. The precision of the whole method provided RSD values below 7.3%, and the accuracy was demonstrated by the analysis of several water samples of different origins, with recoveries ranged from 77 to 98%. Moreover, a remarkable re-usability of the MMIP sorbent, more than 65 uses without losses in extraction capacity, was obtained.
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•Simple one-pot synthesis of a novel magnetic MIP for phenoxy acid herbicides is described.•Magnetic MIP sorbent showed high extraction capacity, good selectivity and excellent reusability.•Magnetic MIP phase coupled to liquid chromatography provided satisfactory recoveries and low LODs.•The magnetic MIP was successfully applied to extract target analytes from environmental water samples.
Ambiguous response formats predict correlations from −.467 to −1 between opposite items, depending on whether the respondent's interpretation of the format is unipolar or bipolar. The authors present ...a procedure to investigate the proper interpretation in each case. It consists of applying nonparametric and parametric item response theory models (the Mokken and the graded response models) to pairs of opposite items in order to find the locations of the response options along the latent scale and, therefore, identify the response format construction. The authors tested this procedure on 4 samples (
N
s = 142-1,150) and 2 item pairs ("relaxed"-"tense" and "optimistic"-"pessimistic"). The results revealed that respondents constructed the formats as bipolar and supported the bipolarity of the item pairs.
El objetivo del presente trabajo es ilustrar cómo la aplicación adecuada o inadecuada del análisis factorial exploratorio (AFE) puede llevar a conclusiones muy diferentes. Para ello se evalúa el ...grado en que cuatro paquetes estadísticos diferentes que permiten realizar AFE de ítems, en concreto SPSS, FACTOR, PRELIS y MPlus, permiten o limitan la aplicación de los estándares actualmente recomendados en materia de análisis factorial. Asimismo se analizan y comparan los resultados que ofrecen dichos programas cuando se factorizan datos empíricos de escalas que ajustan, según el caso, de manera inadecuada, ambigua u óptima a los supuestos del modelo AFE lineal clásico, a través de las distintas posibilidades que ofrecen los distintos programas. Los resultados de la comparación ilustran las consecuencias de elegir entre un programa u otro, y también las consecuencias de elegir entre unas opciones u otras dentro de un mismo programa, en función de la naturaleza de los datos. Finalmente se ofrecen una serie de recomendaciones prácticas dirigidas a los investigadores aplicados con cierta orientación metodológica.
The aim of the present study is to illustrate how the appropriate or inappropriate application of exploratory factor analysis (EFA) can lead to quite different conclusions. To reach this goal, we ...evaluated the degree to which four different programs used to perform an EFA, specifically SPSS, FACTOR, PRELIS and MPlus, allow or limit the application of the currently recommended standards. In addition, we analyze and compare the results offered by the four programs when factor analyzing empirical data from scales that fit the assumptions of the classic linear EFA modeling adequately, ambiguously, or optimally, depending on the case, through the possibilities the different programs offer. The results of the comparison show the consequences of choosing one program or another; and the consequences of selecting some options or others within the same program, depending on the nature of the data. Finally, the study offers practical recommendations for applied researchers with a methodological orientation.
Burnout researchers have proposed that the conceptual opposites of emotional exhaustion and cynicism (the core dimensions of burnout) are vigor and dedication (the core dimensions of engagement), ...respectively (
Maslach & Leiter, 1997; Schaufeli, Salanova, González-Romá, & Bakker, 2002). We tested this proposition by ascertaining whether two sets of items, exhaustion–vigor and cynicism–dedication, were scalable on two distinct underlying bipolar dimensions (i.e., energy and identification, respectively). The results obtained by means of the non-parametric Mokken scaling method in three different samples (
Ns
=
477, 507, and 381) supported our proposal: the core burnout and engagement dimensions can be seen as opposites of each other along two distinct bipolar dimensions dubbed energy and identification.
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•Novel aptamer modified magnetic sorbent for selective isolation of atrazine is proposed.•Aptamers were effectively bonded to vinylized magnetic nanoparticles via thiol-ene click ...reaction.•Sensitive atrazine determination by magnetic solid-phase extraction combined with HPLC-UV.•The magnetic oligosorbent showed satisfactory reusability and recovery.•The optimized protocol was successfully applied to environmental water samples.
In this work, a novel aptamer magnetic sorbent was prepared and used as magnetic solid-phase extraction sorbent for selective isolation of atrazine (ATZ) in water samples. The magnetic oligosorbent was fabricated by immobilizing DNA aptamer onto the surface of vinylized magnetic nanoparticles (VMNPs) via “thiol-ene” click chemistry reaction. After optimization of different aptamer coupling parameters, the following experimental conditions were found to give best results: 100 mg VMNPs incubated with 1 μmol L−1 thiol-modified aptamer for 5 h at 55 °C. The resulting oligosorbent was characterized by different instrumental techniques such as transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR) and inductively coupled plasma mass spectrometry (ICP-MS). Then, several parameters of the extraction protocol were investigated to achieve the best ATZ extraction performance. The optimized aptamer-based magnetic solid-phase extraction (Apt-MSPE) protocol followed by HPLC with diode-array detection gave detection and quantification limits for ATZ of 0.005 µg L−1 and 0.018 µg L−1, respectively. The applicability of this protocol was demonstrated by analyzing several environmental water samples from of different sources with recovery values from 85.5 to 94% and relative standard deviations less than 2.5%. Moreover, the developed Apt-MNPs sorbent could be re-used at least 12 times, without losses in its extraction capacity.
This paper describes the fabrication of a novel microbore monolithic column modified with magnetite nanoparticles (MNPs) prepared in a poly(ethylene-co-tetrafluoroethylene) (EFTE) tubing, and its ...application as stationary phase for the chromatographic separation of phosphorylated compounds. In order to obtain the composite column, a two-step procedure was performed. The formation of a glycidyl methacrylate-based monolith inside the activated ETFE tube was firstly carried out. Then, two incorporation approaches of MNPs in monoliths were investigated. The generic polymer was modified with 3-aminopropyltrimethoxysilane (APTMS) to be subsequently attached to MNP surfaces. Alternatively, APTMS-coated MNPs were firstly prepared and subsequently used for attachment onto the monolith surface through reaction of epoxy groups present in the generic monolith. This last strategy gave a reproducible layer of MNPs coated onto the polymer monolith as well as robust and permeable chromatographic columns. The retention behaviour of this MNP-based composite monolithic column was studied by using small phosphorylated compounds (adenosine phosphates). It was found that the retention of model analytes was ruled by partitioning and adsorption HILIC mechanisms. The columns also exhibited satisfactory performance in the separation of these target compounds, showing good chromatographic behaviour after two months of continued use. These composite monolithic columns were also successfully applied to the extraction of a tryptic digest of β-casein.
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•MNP-modified monoliths were prepared in flexible tube for LC separation and extraction.•The hybrid monolithic columns showed hydrophilic separation features.•The hybrid monoliths were reproducible and stable under micro-bore LC conditions.•The composite columns exhibited satisfactory separation of phosphorylated compounds.•The hybrid monoliths can be satisfactorily used for phosphopeptide enrichment.
•HPLC—chemiluminescence detection of organothiophosphorus pesticides.•High selectivity and sensitivity thanks to the post-column chemiluminescence reaction.•Successful simultaneous determination of ...organothiophosphorus pesticides in water samples in a short analysis time.
A new, fast, selective and sensitive method has been developed for the simultaneous determination of nine organothiophosphorus (OTP) pesticides, namely omethoate, dimethoate, disulfoton-sulfoxide, methidathion, phosmet, malathion, diazinon, pirimiphos-methyl and chlorpyrifos. The pesticides were separated on a Kinetex C18 column by gradient elution with acetonitrile:water. A post-column basic hydrolysis of the pesticides and later a chemiluminescence (CL) reaction with cerium (IV) in acid medium was carried out. Hexadecylpyridinium chloride highly enhanced the CL emission. Under optimized conditions, linearity, precision, limits of detection and quantification, and accuracy were determined. Both selectivity and sensitivity were compared with those obtained with UV detection. In combination with SPE, limits of detection in the range 15–80ng/L and 5–30ng/L were obtained when 250mL and 1000mL of solution were treated, respectively. When applied to 250mL of sample the inter-day precision of the method was between 3.5% and 7.3% and the intra-day precision between 2.9% and 6.0%. The method was applied to determine OTP pesticides in spiked water samples from different origins: irrigation, river, sea, ground, spring, mineral and tap waters, being the percentage of recovery of added amounts near 100% form most of the pesticides.
A polymethacrylate-based sorbent modified with magnetic nanoparticles (MNPs) has been synthesized and used as sorbent for solid-phase extraction (SPE) and magnetic solid-phase extraction (MSPE) of ...three organophosphorus pesticides (phosmet, pirimiphos-methyl, and chlorpyrifos) in water samples followed by high-performance liquid chromatography–diode array detection. The sorbent was prepared from a glycidyl methacrylate-based polymer, modified with a silanizing agent, followed by immobilization of MNPs on the surface of the material. The sorbent was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Comparative studies of this support were done both in conventional SPE cartridge and MSPE approach. Several extraction parameters (loading pH, elution solvent, eluting volume, and loading flow rate) were investigated in detail. Under optimal conditions, the proposed sorbent gave an excellent enrichment efficiency of analytes and detection limits between 0.01 and 0.25 μg L
−1
. The recoveries of organophosphorus pesticides in spiked water samples were in the range of 71–98%, and the developed sorbent showed a high reusability (up to 50 uses without losses in recovery). The proposed method was satisfactorily applied to the analysis of these pesticides in water samples from different sources.
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