Influence of photo-initiators in the preparation of methacrylate monoliths into poly(ethylene-co-tetrafluoroethylene) tubing for microbore HPLC

[EN] In this study, poly(butyl methacrylate-co-ethyleneglycol dimethacrylate) polymeric monoliths were in situ developed within 0.75 mm i.d. poly(ethylene-co-tetrafluoroethylene) (ETFE) tubing by UV polymerization via three different free-radical initiators fscce-azobisisobutyronitrile (AIBN), 2,2-dimethoxy-2-phenylacetophenone (DMPA) and 2-methyl-4'-(methylthio)-2-morpholinopropiophenone (MTMPP). The influence of the nature of each photo-initiator and irradiation time on the morphological features of the polymer was investigated by scanning electron microscopy, and the chromatographic properties of the resulting microbore columns were evaluated using alkyl benzenes as test substances. The beds photo-initiated with MTMPP gave the best performance (minimum plate heights of 38 mu m for alkyl benzenes) and exhibited a satisfactory reproducibility in the chromatographic parameters (RSD < 11%). These monolithic columns were also successfully applied to the separation of phenylurea herbicides, proteins and a tryptic digest of beta-casein. (C) 2019 Elsevier B.V. All rights reserved.This research study has been sponsored by projects PROMETEO/2016/145 (Conselleria d'Educacio, Investigacio, Cultura i Esport, Generalitat Valenciana, Spain) and RTI2018-095536-B-I00 (Ministry of Science, Innovation and Universities, Spain).Catalá-Icardo, M.; Torres-Cartas, S.; Simó-Alfonso, EF.; Herrero-Martínez, JM. (2020). Influence of photo-initiators in the preparation of methacrylate monoliths into poly(ethylene-co-tetrafluoroethylene) tubing for microbore HPLC. Analytica Chimica Acta. 1093:160-167. https://doi.org/10.1016/j.aca.2019.09.055S160167109

Photografted fluoropolymers as novel chromatographic supports for polymeric monolithic stationary phases

[EN] In this study, porous polymer monoliths were in situ synthesized in fluoropolymers tubing to prepare microbore HPLC columns. To ensure the formation of robust homogeneous polymer monoliths in these housing supports, the inner surface of fluoropolymer tubing was modified in a two-step photografting process. Raman spectroscopy and scanning electron microscopy (SEM) confirmed the successful modification of the inner poly(ethylene-co-tetrafluoroethylene) (ETFE) wall and the subsequent attachment of a monolith onto the wall. Poly(glycidyl methacrylate-co-divinylbenzene), poly(butyl methacrylate-co-ethyleneglycol dimethacrylate) and poly(styrene-co-divinylbenzene) monoliths were in situ synthesized by thermal polymerization within the confines of surface vinylized ETFE tubes. The resulting monoliths exhibited good permeability and mechanical stability (pressure resistance up to 9¿MPa). The chromatographic performance of these different monolithic columns was evaluated via the separation of alkyl benzenes and proteins in a conventional HPLC system.This work was supported by project PROMETEO/2016/145 (Conselleria d'Educacio, Investigacio, Cultura i Esport,Esport, Generalitat Valenciana, Spain). The authors also thank Dr. S. Laredo-Ortiz from the Atomic Spectroscopy section of the SCSIE (University of Valencia), for her help in Raman measurements.Catalá-Icardo, M.; Torres-Cartas, S.; Meseguer-Lloret, S.; Simó-Alfonso, E.; Herrero Martínez, J. (2018). Photografted fluoropolymers as novel chromatographic supports for polymeric monolithic stationary phases. Talanta. 187:216-222. doi:10.1016/j.talanta.2018.05.026S21622218

Classification of Pecorino cheeses produced in Italy according to their ripening time and manufacturing technique using Fourier transform infrared spectroscopy.

Fourier-transform infrared spectroscopy, followed by linear discriminant analysis of the spectral data, was used to classify Italian Pecorino cheeses according to their ripening time and manufacturing technique. The Fourier transform infrared spectra of the cheeses were divided into 18 regions and the normalized absorbance peak areas within these regions were used as predictors. Linear discriminant analysis models were constructed to classify Pecorino cheeses according to different ripening stages (hard and semi-hard) or according to their manufacturing technique (fossa and nonfossa cheeses). An excellent resolution was achieved according to both ripening time and manufacturing technique. Also, a final linear discriminant analysis model considering the 3 categories (hard nonfossa, hard fossa, and semi-hard nonfossa) was constructed. A good resolution among the 3 categories was obtained

Determination of a lectin protein allergen in food by on-line aptamer affinity solid-phase extraction capillary electrophoresis-mass spectrometry

An aptamer affinity sorbent was prepared for clean-up, preconcentration, separation and characterization of a food allergen protein by on-line aptamer affinity solid-phase extraction capillary electrophoresis-mass spectrometry (AA-SPE-CE-MS). SPE microcartridges were packed with a sorbent based on magnetic bead particles modified with an aptamer against the target lectin protein concanavalin A (Con A). After optimization of several parameters of the SPE-CE-MS method, the sample (ca. 30 µL) was loaded in separation background electrolyte (BGE, 2 M acetic acid pH 2.2), while the retained protein was eluted with 100 mM NH4OH (pH 11.2) (ca. 100 nL). The developed method was linear between 0.5 and 20 mg·L-1 and the limit of detection (LOD) was 0.25 mg·L-1, which was 100 times lower than by CE-MS. The repeatability of the method was satisfactory, with relative standard deviations (RSD) for migration times and peak areas below 1.9 and 8.1%, respectively. In addition, the microcartridges could be reused more than 25 analyses without significant loss of extraction efficiency. Finally, the applicability and versatility of the developed method were demonstrated by analyzing low levels of Con A in different food matrices (i.e. white beans, as well as chickpea, lentils, and wheat flours), leading to satisfactory results, with recoveries between 87 and 115%

Accurate determination of the milk protein allergen β-lactoglobulin by on-line aptamer affinity solid-phase extraction capillary electrophoresis-mass spectrometry

An on-line aptamer affinity solid-phase extraction capillary electrophoresis-mass spectrometry (AA-SPE-CE-MS) method was developed to purify, preconcentrate, separate, and characterize the milk allergenic protein β-lactoglobulin (β-LG) in food samples. The sorbent to pack into the SPE microcartidges was prepared by immobilizing an aptamer against β-LG onto magnetic bead particles. After optimizing the SPE-CE-MS method, the sample (ca. 75 µL) was loaded in separation background electrolyte (BGE, 2 M acetic acid pH 2.2), while a solution of 100 mM NH4OH (pH 11.2) (ca. 100 nL) was used for the protein elution. The linearity of the method ranged between 0.1 and 20 µg·mL-1 and the limit of detection (LOD) was 0.05 µg·mL-1, which was 200 times lower than by CE-MS. The method was repeatable in terms of relative standard deviation (RSD) for migration times and peak areas (< 0.5 % and 2.4 %, respectively) and microcartridge lifetime was more than 25 analyses. The applicability of the method for the determination of low levels of β-LG was shown by analyzing milk-free foods (i.e. a 100 % cocoa dark chocolate, a hypoallergenic formula for infants, and a dairy-free white bread) and milk-containing white breads. Results were satisfactory in all cases, thus demonstrating the great potential of the developed method for accurate food safety and quality control

Triacylglycerol Analysis in Human Milk and Other Mammalian Species: Small-Scale Sample Preparation, Characterization, and Statistical Classification Using HPLC-ELSD Profiles

In this work, a method for the separation of triacylglycerols (TAGs) present in human milk and from other mammalian species by reversed-phase high-performance liquid chromatography using a core–shell particle packed column with UV and evaporative light-scattering detectors is described. Under optimal conditions, a mobile phase containing acetonitrile/n-pentanol at 10 °C gave an excellent resolution among more than 50 TAG peaks. A small-scale method for fat extraction in these milks (particularly of interest for human milk samples) using minimal amounts of sample and reagents was also developed. The proposed extraction protocol and the traditional method were compared, giving similar results, with respect to the total fat and relative TAG contents. Finally, a statistical study based on linear discriminant analysis on the TAG composition of different types of milks (human, cow, sheep, and goat) was carried out to differentiate the samples according to their mammalian origin

Decreased endostatin in db/db retinas is associated with optic disc intravitreal vascularization

Diabetic retinopathy; Endostatin; Intravitreal vesselsRetinopatia diabètica; Endostatina; Vasos intravítresRetinopatía diabética; Endostatina; Vasos intravítreosEndostatin, a naturally cleaved fragment of type XVIII collagen with antiangiogenic activity, has been involved in the regulation of neovascularization during diabetic retinopathy. Here, the intracellular distribution of endostatin in healthy mouse and human neuroretinas has been analyzed. In addition, to study the effect of experimental hyperglycemia on retinal endostatin, the db/db mouse model has been used. Endostatin protein expression in mouse and human retinas was studied by immunofluorescence and Western blot, and compared with db/db mice. Eye fundus angiography, histology, and immunofluorescence were used to visualize mouse retinal and intravitreal vessels. For the first time, our results revealed the presence of endostatin in neurons of mouse and human retinas. Endostatin was mainly expressed in bipolar cells and photoreceptors, in contrast to the optic disc, where endostatin expression was undetectable. Diabetic mice showed a reduction of endostatin in their retinas associated with the appearance of intravitreal vessels at the optic disc in 50% of db/db mice. Intravitreal vessels showed GFAP positive neuroglia sheath, basement membrane thickening by collagen IV deposition, and presence of MMP-2 and MMP-9 in the vascular wall. All together, these results point that decreased retinal endostatin during experimental diabetes is associated with optic disc intravitreal vascularization. Based on their phenotype, these intravitreal vessels could be neovessels. However, it cannot be ruled out the possibility that they may also represent persistent hyaloid vessels.This work was supported by the Instituto de Salud Carlos III, Ministerio de Ciencia e Innovación, Spain (grant number PI16/00719); the Fundação para a Ciência e a Tecnologia, Ministerio da Educação e Ciência, Portugal (grant numbers SFRH/BD/95330/2013 and SFRH/BPD/102573/2014); and Fondo Europeo de Desarrollo Regional (FEDER)

Recent Advances in Molecularly Imprinted Membranes for Sample Treatment and Separation

[EN] 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.This work was supported by project RTI2018-095536-B-I00 (Ministry of Science, Innovation and Universities, Spain).Torres-Cartas, S.; Catalá-Icardo, M.; Meseguer-Lloret, S.; Simó-Alfonso, EF.; Herrero-Martínez, JM. (2020). Recent Advances in Molecularly Imprinted Membranes for Sample Treatment and Separation. Separations. 7(4):1-28. https://doi.org/10.3390/separations7040069S1287

Extraction and preconcentration of organophosphorus pesticides in water by using a polymethacrylate-based sorbent modified with magnetic nanoparticles

[EN] 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 &#956;g L&#8722;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.This work was supported by projects CTQ2014-52765-R (MINECO of Spain and FEDER) and PROMETEO/2016/145 (Conselleria de Educacion, Investigacion, Cultura y Deporte of Generalitat Valenciana, Spain).Meseguer-Lloret, S.; Torres-Cartas, S.; Catalá-Icardo, M.; Simó-Alfonso, EF.; Herrero-Martínez, JM. (2017). Extraction and preconcentration of organophosphorus pesticides in water by using a polymethacrylate-based sorbent modified with magnetic nanoparticles. 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Physical chemical properties and kinetics of redox processes in water/soybean oil microemulsions

Water/oil microemulsions (w/o ME) constituted by water, soybean oil, SDS (sodium dodecyl sulfate) and several short-chain alcohols were characterized from the viewpoint of its physical-chemical and electroanalytical properties. Different co-surfactants and surfactant:co-surfactant ratios were used, and the ME with the most favourable composition was used to study the kinetics of redox processes. For this purpose, cyclic voltammetry measurements using a Pt disk working ultramicroelectrode, an Ag/AgCl reference electrode and a Pt auxiliary electrode, and ferrocene as a probe, were performed. It was verified that the thermodynamic stability of the MEs increases with the co-surfactant content. The molecular structure and water solubility of the co-surfactant affect the electrical conductivity and the hydrodynamic radio of the MEs. Owing to the low diffusion coefficients verified in the MEs, measurements in transient state using conventional sweeping rates could be performed. Ferrocene oxidation in the ME has been demonstrated to proceed in quasi-reversibility conditions. Thus, the possibility of carrying out studies of cyclic voltammetry in vegetable oils under the w/o ME form was demonstrated