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Use of dispersive liquid–liquid microextraction for the determination of carbamates in juice samples by sweeping-micellar electrokinetic chromatography
(Springer, 2011-01-31) Moreno-González, David; Gámiz-Gracia, Laura; García-Campaña, Ana M.; Bosque-Sendra, Juan Manuel
Dispersive liquid–liquid microextraction (DLLME) has been proposed for the extraction and preconcentra- tion of 12 carbamate pesticides in juice samples, followed by their determination by micellar electrokinetic chromatography with diode-array detection. To improve sensitivity, an on-capillary sample concentration method based on sweeping has been developed. Also, separations were performed in an extended light path fused-silica capillary; the separation buffer consisted of 100 mM borate and 50 mM SDS (pH 9.0) with 5% acetonitrile. Samples were introduced by hydrodynamic injection, dissolved in the separation buffer, but free of micelles. Several parameters of the DLLME procedure (such as type and volume of extraction and dispersive solvents, pH, salt addition, and extraction time) were optimized. Recoveries obtained for fortified juice samples (banana, pineapple, and tomato) at three different concentration levels, ranged from 78% to 105%, with relative standard deviations lower than 9%. The limits of detection ranged from 1 to 7 μg l−1. Moreover, the method is fast, simple, and environmentally friendly.
Simultaneous Testing of Multiclass Organic Contaminants in 4 Food and Environment by Liquid Chromatography/ Dielectric 5 Barrier Discharge Ionization- Mass Spectrometry
(RSC, 2012) Gilbert-López, Bienvenida; García-Reyes, Juan Francisco; Meyer, Cordula; Michels, Antje; Franzke, Joachim; Molina-Díaz, Antonio; Hayen, Heiko
A Dielectric Barrier Discharge Ionization (DBDI) LC/MS interface is based on the use of a lowtemperature helium plasma, which features the possibility of simultaneous ionization of species with a wide variety of physicochemical properties. In this work, the performance of LC/DBDI-MS for trace analysis of highly relevant species in food and environment has been examined. Over 75 relevant species including multiclass priority organic contaminants and residues such as pesticides, polycyclic aromatic hydrocarbons, organochlorine species, pharmaceuticals, personal care products, and drugs of abuse were tested. LC/DBDI-MS performance for this application was assessed and compared with standard LC/MS sources (electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI)). The used benchtop Orbitrap mass spectrometer features a 10 Hz polarity switching mode, so that both positive and negative ion mode acquisitions are possible with acquisition cycles matching the requirements of fast liquid chromatography. Both polar and nonpolar species (including those typically analyzed by GC/electron ionization-MS) can be tested in a single run using polarity switching mode. The methodology was found to be effective in detecting a wide array of organic compounds at concentration levels in the low ng L-1 to mg kg-1 range in wastewater and food matrices, respectively. The linearity was evaluated in an olive oil extract, obtaining good correlation coefficients in the studied range. Additionally, minor matrix effects (<=15% of signal suppression or enhancement) were observed for most of the studied analytes in this complex fatty matrix. The results obtained were compared with data from both ESI and APCI sources, obtaining a merged coverage between ESI and APCI in terms of analyte ionization and higher overall sensitivity for the proposed ion source based on the DBD principle. The use of this approach further extends the coverage of current LC/MS methods towards an even larger variety of chemical species including both polar and nonpolar (non-ESI amenable) species and may find several applications in fields such as food and environment testing or metabolomics where GC/MS and LC/MS are combined to cover as many different species as possible.
Dispersive liquid-liquid microextraction using a low density extraction solvent for the determination of 17 N-methylcarbamates by micellar electrokinetic chromatography-electrospray-mass spectrometry employing a volatile surfactant.
(Elsevier, 2012-07) Moreno-González, David; Gámiz-Gracia, Laura; Bosque-Sendra, Juan M; García-Campaña, Ana M.
A new analytical method based on micellar electrokinetic chromatography tandem mass spectrometry (MEKC–ESI–MS/MS) employing a MS friendly surfactant (ammonium perfluorooctanoate) is proposed and validated for the identification and simultaneous quantification of 17 N-methylcarbamate pesticides in environmental and drinking water samples. MS/MS detection using an ion trap as analyzer operating in the multiple reaction monitoring mode was used. Different parameters were optimized in order to obtain an adequate CE separation combined with the highest sensitivity in MS/MS. Dispersive liquid–liquid microextraction (DLLME) using a low-density extraction solvent has been proposed for extraction, obtaining a preconcentration factor of 10. Under optimum conditions, recoveries for fortified samples ranged from 83% to 101%, with relative standard deviations lower than 8%. The limits of detection ranged from 1 to 144 ng l−1, demonstrating the sensitivity and applicability of this fast, simple, and environmentally friendly method.
Ultrasound-assisted surfactant-enhanced emulsification microextraction for the determination of carbamates in wines by ultra-high performance liquid chromatography–tandem mass spectrometry
(Elsevier, 2013) Moreno-González, David; Huertas-Pérez, José F.; García-Campaña, Ana M.; Gámiz-Gracia, Laura
A new sensitive multiresidue method based on ultra-high performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) has been developed for the detection, confirmation and quantification of twenty five carbamates in wine samples. The separation was achieved in 5.5 min, using a Zorbax Eclipse plus RRHD C18 column (50 mm × 2.1 mm, 1.8 μm), with a mobile phase of water and methanol, both of them with 0.01% formic acid. The analytes were detected in positive mode with multiple reaction monitoring mode. Ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME), using a low-density extraction solvent has been optimized for the satisfactory extraction of carbamates and clean-up of extracts. The matrix effect was studied, showing that the proposed procedure provides very clean extracts. Under optimum conditions, recoveries for fortified wine samples ranged from 74 to 102%, with relative standard deviations lower than 6%. Limits of quantification ranged from 0.15 to 0.92 μg l−1, showing the high sensitivity of this fast and simple method and its compliance with current requirements.
Self-assembly structures of 1H-indazoles in solution and solid phases: A vibrational (IR, FarIR, Raman and VCD) and computational study
(Wiley, 2013) Avilés-Moreno, Juan Ramón; Quesada-Moreno, María del Mar; López-González, Juan Jesús; Claramunt, Rosa M.; López-García, Concepción; Alkorta, Ibon; Elguero, José
1H-indazoles are good candidates to study phenomena of molecular association and spontaneous resolution of chiral compounds. Thus, because the 1H-indazoles can crystallize forming dimers, trimers or catemers, depending on their structure and the phase where they are, the difficulty of the experimental analysis of the structure of the family of 1H-indazoles is clear. This lead to contemplate several questions: How can we determine the presence of different structures of a determined molecular species if they change according to the phase? Could these different structures be present in the same phase simultaneously? How can it be determined? In order to shed light on these questions, we outline a very complete strategy by using different techniques of vibrational spectroscopy sensitive (VCD) and not sensitive (IR, FarIR and Raman) to the chirality together with quantum chemical calculations.
Conformational preference and chiroptical response of Carbohydrates D-Ribose and 2-Deoxy-D-ribose in aqueous and solid phases
(American Chemical Society, 2013) Quesada-Moreno, María del Mar; Azofra, Luis Miguel; Avilés-Moreno, Juan Ramón; Alkorta, Ibon; Elguero, José; López-González, Juan Jesús
This work targets the structural preferences of D-ribose and 2-deoxy-D-ribose in water solution and solid phase. A theoretical DFT (B3LYP and M06-2X) and MP2 study has been undertaken considering the five possible configurations (open-chain, α-furanose, β-furanose, α-pyranose, and β-pyranose) of these two carbohydrates with a comparison of the solvent treatment using only a continuum solvation model (PCM) and the PCM plus one explicit water molecule. In addition, experimental vibrational studies using both nonchiroptical (IR-Raman) and chiroptical (VCD) techniques have been carried out. The theoretical and experimental results show that α-and β-pyranose forms are the dominant configurations for both compounds. Moreover, it has been found that 2-deoxy-D-ribose presents a non-negligible percentage of open-chain forms in aqueous solution, while in solid phase this configuration is absent.
Ambient Diode Laser Desorption Dielectric Barrier Discharge Ionization Mass Spectrometry of Nonvolatile Chemicals
(ACS Publications, 2013-02-19) Gilbert-López, Bienvenida; Schilling, Michael; Alhmann, Norman; Michels, Antje; Hayen, Heiko; Molina-Díaz, Antonio; García-Reyes, Juan Francisco; Franzke, Joachim
In this work, the combined use of desorption by a continuous wave near-infrared diode laser and ionization by a dielectric barrier discharge-based probe (laser desorption dielectric barrier discharge ionization mass spectrometry (LD-DBDI-MS)) is presented as an ambient ionization method for the mass spectrometric detection of nonvolatile chemicals on surfaces. A separation of desorption and ionization processes could be verified. The use of the diode laser is motivated by its low cost, ease of use, and small size. To achieve an efficient desorption, the glass substrates are coated at the back side with a black point (target point, where the sample is deposited) in order to absorb the energy offered by the diode laser radiation. Subsequent ionization is accomplished by a helium plasmajet generated in the dielectric barrier discharge source. Examples on the application of this approach are shown in both positive and negative ionization modes. A wide variety of multiclass species with low vapor pressure were tested including pesticides, pharmaceuticals and explosives (reserpine, roxithromycin, propazine, prochloraz, spinosad, ampicillin, dicloxacillin, enrofloxacin, tetracycline, oxytetracycline, erythromycin, spinosad, cyclo-1,3,5,7-tetramethylene tetranitrate (HMX), and cyclo-1,3,5-trimethylene trinitramine (RDX)). A comparative evaluation revealed that the use of the laser is advantageous, compared to just heating the substrate surface.
Micellar electrokinetic chromatography–electrospray ionization mass spectrometry employing a volatile surfactant for the analysis of amino acids in human urine
(Wiley, 2013-09) Moreno-González, David; Sastre Toraño, Javier; Gámiz-Gracia, Laura; García-Campaña, Ana M.; de Jong, Gerhardus J.; Somsen, Govert W.
A new MEKC-ESI-MS method for the analysis of amino acids (AAs) in human urine was developed employing ammonium perfluorooctanoate (APFO) as volatile surfactant. The influence of APFO on the MS signal of AAs was evaluated by infusion experiments, which showed that APFO hardly affects analyte responses and presents significantly less ion suppression than equal concentrations of ammonium acetate. In order to obtain efficient separation of AAs, MEKC parameters such as the pH and APFO concentration of the BGE, were optimized. Optimum AA resolution, including baseline separation of leucine and isoleucine, was obtained using 150 mM APFO (pH 9.0) as BGE, representing a considerable selectivity improvement over CE using 50 mM ammonium acetate (pH 9.0). Optimization of CE-MS parameters, such as sheath liquid composition and flow rate, and ESI and MS settings, led to LODs ranging from 9 to 26 ng/mL for the 20 tested AAs, which is highly favorable for an MEKC-MS method. Good linearity (r2 > 0.99) and repeatability were obtained for all AAs tested with RSD values of 3.0–6.7% for peak area and <1.5% for migration time. The applicability of the MEKC-MS method was demonstrated by the quantitative determination of AAs in urine employing only a 1:1 dilution with BGE as sample pretreatment. All AAs could selectively be detected and quantified obtaining relevant concentration values for normal human urine.
MICELLAR ELECTROKINETIC CHROMATOGRAPHY–ELECTROSPRAY IONIZATION MASS SPECTROMETRY EMPLOYING A VOLATILE SURFACTANT FOR THE ANALYSIS OF AMINO ACIDS IN HUMAN URINE
(Wiley, 2013-09) Moreno-González, David; Sastre Toraño, Javier; Gámiz-Gracia, Laura; García-Campaña, Ana M.; de Jong, Gerhardus J.; Somsen, Govert W.
A new MEKC-ESI-MS method for the analysis of amino acids (AAs) in human urine was developed employing ammonium perfluorooctanoate (APFO) as volatile surfactant. The influence of APFO on the MS signal of AAs was evaluated by infusion experiments, which showed that APFO hardly affects analyte responses and presents significantly less ion suppression than equal concentrations of ammonium acetate. In order to obtain efficient separation of AAs, MEKC parameters such as the pH and APFO concentration of the BGE, were optimized. Optimum AA resolution, including baseline separation of leucine and isoleucine, was obtained using 150 mM APFO (pH 9.0) as BGE, representing a considerable selectivity improvement over CE using 50 mM ammonium acetate (pH 9.0). Optimization of CE-MS parameters, such as sheath liquid composition and flow rate, and ESI and MS settings, led to LODs ranging from 9 to 26 ng/mL for the 20 tested AAs, which is highly favorable for an MEKC-MS method. Good linearity (r2 > 0.99) and repeatability were obtained for all AAs tested with RSD values of 3.0–6.7% for peak area and <1.5% for migration time. The applicability of the MEKC-MS method was demonstrated by the quantitative determination of AAs in urine employing only a 1:1 dilution with BGE as sample pretreatment. All AAs could selectively be detected and quantified obtaining relevant concentration values for normal human urine.
Molecularly imprinted polymer as in-line concentrator in capillary electrophoresis coupled with mass spectrometry for the determination of quinolones in bovine milk samples
(Elsevier, 2014-09) Moreno-González, David; Lara, Francisco J.; Gámiz-Gracia, Laura; García-Campaña, Ana M.
In this work molecularly imprinted polymers have been evaluated as sorbent for the construction of an in-line solid phase extraction analyte concentrator in capillary electrophoresis coupled with mass spectrometry for the determination of the eight regulated veterinary quinolones in bovine milk samples. Different parameters affecting the analyte concentrator performance, such as sample pH, volume and composition of the elution plug and injection time, were studied. Sample volumes of 22 μL (2 bar for 15 min) were loaded on the MISPE microcartridge and the retained analytes were eluted by injecting a plug of MeOH/H2O/NH3 (60/37/3 by volume) for 125 s at 50 mbar (60 nL). The proposed method is simple for the monitoring of these antibiotic residues in milk samples, allowing the direct injection of the samples with minimum sample pretreatment, achieving limits of detection between 3.8 and 4.7 μg kg−1 and unequivocal identification of the compounds working in tandem mass spectrometry. Recoveries ranging from 70.0 to 102.3% were obtained and satisfactory intra-day and inter-day RSDs were achieved (≤12% and 15% respectively). Reproducibility among different constructed analyte concentrators showed RSD ≤ 11%
Molecularly imprinted polymer as in-line concentrator in capillary electrophoresis coupled with mass spectrometry for the determination of quinolones in bovine milk samples
(Elsevier, 2014-09) Moreno-González, David; Lara, Francisco J.; Gámiz-Gracia, Laura; García-Campaña, Ana M.
In this work molecularly imprinted polymers have been evaluated as sorbent for the construction of an in-line solid phase extraction analyte concentrator in capillary electrophoresis coupled with mass spectrometry for the determination of the eight regulated veterinary quinolones in bovine milk samples. Different parameters affecting the analyte concentrator performance, such as sample pH, volume and composition of the elution plug and injection time, were studied. Sample volumes of 22 μL (2 bar for 15 min) were loaded on the MISPE microcartridge and the retained analytes were eluted by injecting a plug of MeOH/H2O/NH3 (60/37/3 by volume) for 125 s at 50 mbar (60 nL). The proposed method is simple for the monitoring of these antibiotic residues in milk samples, allowing the direct injection of the samples with minimum sample pretreatment, achieving limits of detection between 3.8 and 4.7 μg kg−1 and unequivocal identification of the compounds working in tandem mass spectrometry. Recoveries ranging from 70.0 to 102.3% were obtained and satisfactory intra-day and inter-day RSDs were achieved (≤12% and 15% respectively). Reproducibility among different constructed analyte concentrators showed RSD ≤ 11%.
Determination of carbamates in edible vegetable oils by ultra-high performance liquid chromatography-tandem mass spectrometry using a new clean-up based on zirconia for QuEChERS methodology
(Elsevier, 2014-10) Moreno-González, David; Huertas-Pérez, José F.; García-Campaña, Ana M.; Gámiz-Gracia, Laura
In this study a fast, selective and sensitive multiresidue method based on QuEChERS methodology has been evaluated and validated for the determination of carbamate pesticides, in edible vegetable oils by UHPLC–MS/MS. A new clean-up sorbent, SupelTM QuE Z-Sep+, has been successfully applied in vegetable oil extracts. Z-Sep+ was compared with other sorbents (i.e. mixture of C18 and PSA) previously used for dispersive solid phase extraction of these matrices, reducing more effectively matrix effects without a significant decrease of analyte recoveries. Matrix effect was studied in different matrices (extra-virgin olive, sunflower, maize, linseed and sesame oil) being ≤│30│% for most of the studied pesticides. Under optimum conditions, recoveries ranged from 74% to 101%, with relative standard deviations lower than 10%. Limits of quantification ranged from 0.09 to 2.0 µg kg−1, allowing their determination at the low concentration levels demanding by current legislation.
Understanding the Aldo-Enediolate Tautomerism of Glycolaldehyde in Basic Aqueous Solutions
(Wiley, 2015) Azofra, Luis Miguel; Quesada-Moreno, María del Mar; Alkorta, Ibon; Avilés-Moreno, Juan Ramón; Elguero, José; López-González, Juan Jesús
The biochemically important interconversion process between aldoses and ketoses is assumed to take place via 1,2-enediol or 1,2-enediolate intermediates, but such intermediates have never been isolated. The current work was undertaken in an attempt to detect the presence of the 1,2-enediol structure of glycolaldehyde in alkaline medium, actually a 1,2-enediolate, and to try to clarify the scarce data existing about both the formation of the deprotonated enediol and the aldo-enediolate equilibrium. The Raman spectra of neutral and basic solutions were recorded as a function of time for eleven days. Several bands associated with the presence of the enediolate were observed in alkaline medium. Glycolaldehyde exists as three different structures in aqueous solution at neutral pH, i.e. hydrated aldehydes, aldehydes and dimers, with a respective ratio of approximately 4:0.25:1. Additionally, the formation of Z-enediolate forms takes place at basic pH, together with the increase of aldehyde species, as 2-oxoethan-1-olate, and the decrease of hydrated aldehyde and dimeric forms. The theoretical ratio ~1.5:1 aldehyde:Z-enediolate reproduces the experimental Raman spectrum in basic medium, with the additional contribution of the previously mentioned ratio between hydrated aldehyde and dimeric forms. Finally, Raman spectroscopy allowed us to monitor the enolization of this carbohydrate model and to conclude that the aldo-enediol tautomerism, formally aldo-enediolate, happens when a suitable amount of basic species is added.
A magnetic-based dispersive micro-solid-phase extraction method using the metal-organic framework HKUST-1 and ultra-high-performance liquid chromatography with fluorescence detection for determining polycyclic aromatic hydrocarbons in waters and fruit tea infusions
(Elsevier, 2016-03) Rocío-Bautista, Priscilla; Pino, Verónica; Ayala-Díaz, Juan; Pasán, Jorge; Ruiz-Pérez, Catalina; Afonso, Ana M.
A hybrid material composed by the metal-organic framework (MOF) HKUST-1 and Fe3O4 magnetic nanoparticles (MNPs) has been synthetized in a quite simple manner, characterized, and used in a magnetic-assisted dispersive micro-solid-phase extraction (M-d-μSPE) method in combination with ultra-high-performance liquid chromatography (UHPLC) and fluorescence detection (FD). The application was devoted to the determination of 8 heavy polycyclic aromatic hydrocarbons (PAHs) in different aqueous samples, specifically tap water, wastewaters, and fruit tea infusion samples. The overall M-d-μSPE-UHPLC-FD method was optimized and validated. The method is characterized by: its simplicity in both the preparation of the hybrid material (simple mixing) and the magnetic-assisted approach (∼10 min extraction time), the use of low sorbent amounts (20 mg of HKUST-1 and 5 mg of Fe3O4 MNPs), and the low organic solvent consumption in the overall M-d-μSPE-UHPLC-FD method (1.5 mL of acetonitrile in the M-d-μSPE method and 2.8 mL of acetonitrile in the UHPLC-FD run). The resulting method has high sensitivity, with LODs down to 0.8 ng L−1; adequate intermediate precision, with relative standard deviation values (RSD) always lower than 6.3% (being the range 5.9–9.0% in tap water for a spiked level of 45 ng L−1, 6.1–14% in wastewaters for a spiked level of 45 ng L−1, and 7.2–17% in fruit tea infusion samples for a spiked level of 45 ng L−1); and adequate relative recoveries, with average values of 82% in tap water, and 94% and 75% in wastewater and fruit tea infusion samples, respectively, if using the proper matrix-matched calibration.
Evaluation of processing factors for selected organic contaminants during virgin olive oil production: Distribution of BTEXS during olives processing
(Elsevier, 2016-05-15) López-Blanco, Rafael; Gilbert-López, Bienvenida; Rojas-Jiménez, Rubén; Robles-Molina, José; Ramos-Martos, Natividad; García-Reyes, Juan Francisco; Molina-Díaz, Antonio
The presence of BTEXS (benzene, toluene, ethylbenzene, xylenes and styrene) in virgin olive oils can be attributed to environmental contamination, but also to biological processes during oil lipogenesis (styrene). In this work, the processing factor of BTEXS from olives to olive oil during its production was evaluated at lab-scale with an Abencor system. Benzene showed the lowest processing factor (15%), whereas toluene and xylenes showed an intermediate behavior (with 40–60% efficiency), and ethylbenzene and styrene were completely transferred (100%). In addition, an attempt to examine the contribution of potential sources to olives contamination with BTEXS was carried out for the first time. Two types of olives samples were classified according to their proximity to the contamination source (road). Although higher levels of BTEXS were found in samples close to roads, the concentrations were relatively low and do not constitute a major contribution to BTEXS usually detected in olive oil.
Supramolecular organization of perfluorinated 1H-indazoles in the solid state using X-ray crystallography, SSNMR and sensitive (VCD) and non sensitive (MIR, FIR and Raman) to chirality vibrational spectroscopies
(Royal Society of Chemistry, 2017) Quesada-Moreno, María del Mar; Avilés-Moreno, Juan Ramón; López-González, Juan Jesús; Jacob, Kane; Vendier, Laure; Etienne, Michel; Alkorta, Ibon; Elguero, José; Claramunt, Rosa M.
1H-Indazole derivatives exhibit a remarkable property since some of them form chiral supramolecular structures starting from achiral monomers. The present work deals with the study of three perfluorinated 1H-indazoles that resolve spontaneously as conglomerates. These conglomerates can contain either a pure enantiomer (one helix) or a mixture of both enantiomers (both helices) with an enantiomeric excess (e.e.) of one of them. The difficulty of the structural analysis of these types of compounds is thus clear. We outline a complete strategy to determine the structures and configurations (M or P helices) of the enantiomers (helices) forming the conglomerates of these perfluorinated 1H-indazoles based on X-ray crystallography, solid state NMR spectroscopy and different solid state vibrational spectroscopies that are either sensitive (VCD) or not (FarIR, IR and Raman) to chirality, together with quantum chemical calculations (DFT).
Conformational Flexibility of Limonene Oxide Studied By Microwave Spectroscopy
(Wiley, 2017) Loru, Donatella; Quesada-Moreno, María Mar; Avilés-Moreno, Juan Ramón; Jarman, Natasha; Huet, Thérèse R.; López-González, Juan Jesús; Sanz, María Eugenia
Monoterpenoids are biogenic volatile organic compounds (BVOCs) that play a major role in atmospheric chemistry, participating in the formation of aerosols. In this work, the monoterpenoid R-(+)-limonene oxide (C10H16O) has been characterized in the gas phase by Fourier transform microwave spectroscopy in a supersonic jet. Five conformers of limonene oxide, four equatorial and one axial considering the configuration of the isopropenyl group, have been unambiguously identified from the analysis of the rotational spectrum. The observed conformers include cis and trans forms, and are stabilised by a subtle balance of hydrogen bonds, dispersive interactions and steric effects. Estimated conformational relative abundances surprisingly reveal that the axial conformer has an abundance similar to some equatorial conformers. In addition, the potential energy surface was extensively explored using density functional theory and ab initio methods.
Gold-Nanoparticles-based Solid-Phase Microextraction Coatings for Determining Organochlorine Pesticides in Aqueous Environmental Samples
(wiley, 2017-03) Gutiérrez-Serpa, Adrián; Rocío-Bautista, Priscilla; Pino, Verónica; Jiménez-Moreno, Francisco; Jiménez-Abizanda, Ana Isabel
The use of solid-phase microextraction coatings based on gold nanoparticles was investigated, focusing the attention on the preparation of nanoparticles with nonclassical reduction agents of HAuCl4 such as gallic acid and H2O2, rather than the conventional sodium citrate. All nanoparticles were characterized by diode array spectroscopy, whereas novel nanoparticles prepared with gallic acid and H2O2 were also characterized by microscopic techniques. Solid-phase microextraction coatings were prepared with a layer-by-layer approach. Gallic acid permitted the preparation of stable nanoparticles with milder experimental conditions (1 min, room temperature) and provided the most uniform coatings (thickness ∼3 μm). Seven organochlorine pesticides were determined in different environmental waters using gas chromatography with electron capture detection. Despite the low thickness of the coatings, limits of detection of the entire method down to 0.13 μg/L were obtained. A comparison with the commercial polyacrylate in terms of the partition coefficients of the analytes to the coatings gave logarithm of the partition coefficient values two times higher with gallic acid than polyacrylate (although the commercial fiber is 28 times thicker). Interfiber relative standard deviation values ranged from 8.67 to 21.3%. Optimum fibers also presented an adequate lifetime (>100 extractions).
Evaluation of hydrophilic interaction liquid chromatography–tandem mass spectrometry and extraction with molecularly imprinted polymers for determination of aminoglycosides in milk and milk-based functional foods
(Elsevier, 2017-08-15) Moreno-González, David; Hamed, Ahmed M.; García-Campaña, Ana M.; Gámiz-Gracia, Laura
An analytical method for the determination of eleven aminoglycosides in different types of milk and milk-based functional products has been optimized and validated. A hydrophilic interaction chromatography (HILIC) column was proposed for the separation of analytes by ultra-high performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS). A commercially molecularly imprinted polymer has been used for the solid phase extraction of the analytes, in order to achieve high selectivity in the sample treatment. The proposed method was characterized for different types of milk (whole cow milk, skimmed cow milk, whole goat milk) and functional dairy products, such as follow-on milk, Omega 3-enriched milk and isoflavones-enriched milk. Matrix effect was studied in the different matrices, being lower than │15│% in all cases, showing that the proposed procedure provided very clean extracts. Limits of quantification in the range 4.2–49 µg kg−1 were estimated, well below the maximum residue limits established by the European Union. Recoveries ranged from 70% to 106% with RSD lower than 13%, in compliance with the current legislation. The combination of HILIC to solve the difficulties of the separation of these very polar compounds in reverse phase with the use of MISPE for sample treatment and MS/MS detection provided a very sensitive, highly selective, robust and useful method for identification and quantification of aminoglycoside residues in different types of milk and milk-based products.
Fully Compatible and Ultra-Sensitive Micellar Electrokinetic Chromatography-Tandem Mass Spectrometry Using Sheathless Porous-Tip Interfacing
(Elsevier, 2017-11-17) Moreno-González, David; Haselberg, Rob; Gámiz-Gracia, Laura; García-Campaña, Ana M.; de Jong, Gerhardus J.; Somsen, Govert W.
The on-line coupling of micellar electrokinetic chromatography and mass spectrometry (MEKC-MS) is often hampered by incompatibility problems leading to reduced separation performance and unfavorable limits of detection (LODs). Here we propose a new selective and highly sensitive MEKC-MS/MS method employing a sheathless porous-tip interface in combination with a micellar phase comprised of semi-volatile surfactant molecules. Carbamate pesticides (CRBs) were selected as representative model compounds being neutral toxic pollutants potentially present at trace levels in environmental water samples. A background electrolyte of 75 mM perfluorooctanoic acid adjusted to pH 9.0 with ammonium hydroxide allowed efficient separation of 15 CRBs and appeared fully compatible with electrospray ionization (ESI)-MS. Interfacing parameters, such as the distance between the capillary tip and mass-spectrometer inlet, ESI voltage, and dry gas temperature and flow were optimized in order to attain good spray stability and high analyte signal-to-noise ratios. For CRBs the LODs ranged from 0.2 to 3.9 ng L−1 (13 nL injected, i.e., 2% of capillary volume), representing an improvement for certain CRBs of more than 300-fold when compared with conventional sheath-liquid interfacing. Good linearity (R2 > 0.99) and satisfactory reproducibility were obtained for all CRBs with interday RSD values for peak area and migration time of 4.0–11.3% and below 1.5%, respectively. Analysis of spiked mineral water showed that the new MEKC-MS/MS method allows selective and quantitative determination of CRB concentrations below the maximum residue limit of 100 ng L−1 without the need for sample preconcentration.

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