Determination of carbamates at trace levels in water and cucumber by capillary liquid chromatography

Posted on 23 November, 2011 by fqm302

A sensitive and reliable method using capillary HPLC with UV-diode array detection (DAD) has been developed and validated for trace determination of carbamate pesticides in cucumber and environmental water samples. The analytes, including carbofuran, carbaryl, methiocarb, promecarb, benthiocarb and fenoxycarb, present legal residue levels regulated by the EU Council Directive 98/83/EC on drinking water and by the Regulation (EC) No. 396/2005 on vegetables. A previous off-line solid-phase extraction (SPE) procedure was required for preconcentration and sample clean-up. The separation was achieved using a C18 column (150 mm × 0.5 mm I.D, 5 µm particle size) and a mobile phase consisting of ACN : water using gradient mode, with a flow rate of 10 µl min−1. Taking advantages of the characteristics of capillary HPLC, low volume of sample and solvents were required, achieving limits of detection for the studied compounds ranged from 10.0–29.6 ng l−1 for water samples and 1.8–5.6 µg kg−1 for cucumber, using UV-detection. Recoveries studies for fortified samples, at three different concentration levels, were carried out obtaining recoveries ranging from 70.0 to 111.1% and relative standard deviations (RSDs) lower than 10.6%.

Posted in Capillary HPLC, Carbamates, Chromatography, Food, Pesticides, SPE, UV-vis, Vegetables, Water | Comments Off on Determination of carbamates at trace levels in water and cucumber by capillary liquid chromatography

Comparison of different sample treatments for the analysis of ochratoxin A in wine by capillary HPLC with laser-induced fluorescence detection

Posted on 2 November, 2011 by fqm302

Ochratoxin A (OTA) is a mycotoxin naturally found in various foods, including wine. As OTA is considered as a possible human carcinogen, the maximum concentration for this compound has been established at 2 μg kg−1 in wine by the EU (Directive (CE) No 1881/2006). Typically, immunoaffinity columns have been used for its extraction. However, simpler, more efficient and less contaminant extraction systems are demanding. In this work, dispersive liquid–liquid microextraction using ionic liquid as extractant solvent (IL-DLLME) and the QuEChERS procedure, have been evaluated and compared for extraction of OTA in wine samples. Laser-induced fluorescence (LIF, He–Cd Laser excitation at 325 nm) coupled with capillary HPLC has been used for the determination of OTA, using a sodium dodecyl sulfate micellar solution in the mobile phase to increase the fluorescence intensity. Matrix-matched calibration curves were established for both methods, obtaining LODs (3× S/N) of 5.2 ng·L−1 and 85.7 ng·L−1 for IL-DLLME and QuEChERS, respectively. Clean extracts were obtained for white, rose and red wines with both methods, with recoveries between 88.7–94.2% for IL-DLLME and between 82.6–86.2% for QuEChERS. The precision was evaluated in terms of repeatability (n = 9) and intermediate precision (n = 15), being ≤ 8.5% for IL-DLLME and ≤ 5.4% for QuEChERS.

Posted in Capillary HPLC, DLLME, Ionic liquids, LIF, Mycotoxins, QuEChERS, Wine | Tagged | Comments Off on Comparison of different sample treatments for the analysis of ochratoxin A in wine by capillary HPLC with laser-induced fluorescence detection

Desarrollo de un método MEKC para la determinación de 5-nitroimidazoles en aguas de río

Posted on 20 September, 2011 by fqm302

Los 5-nitroimidazoles (5-NDZs) son antimicrobianos con propiedades antibacterianas y antiprotozoarias. Debido a estas características se ha extendido su uso tanto como antibióticos humanos como veterinarios, mostrando eficacia contra la mayoría de bacterias anaerobias Gram negativas y algunas Gram positivas (Bacteroides grupo fragilis, Fusobacterium spp., Clostridium spp., Veilonella spp., incluyendo Clostridium difficile y C. perfringens), así como contra protozoos tales como Trichomonas vaginalis, Entamoeba hitolytica, Guardia lamblia y Balantidium coli.

Existen informes que atribuyen propiedades genotóxicas, mutagénicas y carcinogénicas a los 5-NDZs. Además, se trata de compuestos de alta solubilidad en el agua y baja biodegradabilidad, lo que favorece su bioacumulación. Estos problemas, además de la aparición de resistencias bacterianas a los 5-NDZs, han llevado a la Unión Europea (UE) a prohibir la utilización de estas sustancias como antibióticos veterinarios.

Pese a esta prohibición, la Agencia de Seguridad Alimentaria Europea (EFSA) sigue registrando aletas sobre alimentos de origen animal que contienen trazas de 5-NDZs. Esto supone que actualmente se está incumpliendo el Reglamento (UE) Nº37/2010, el cual establece que cualquier alimento de origen animal destinado al consumo humano debe estar exento de este tipo de antibióticos.

Como medida de control, y con objeto de garantizar el cumplimiento de la legislación vigente, se requieren de métodos analíticos que permitan la detección y cuantificación de los 5-NDZs, tanto en muestras de origen alimentario como medio ambiental. Por este motivo se ha desarrollado, dentro del Grupo de Investigación “Química Analítica Alimentaria, Ambiental y Clínica (FQM-302)”, un método analítico para la determinación de los mencionados antibióticos., el cual es descrito en la presente Memoria.

El método desarrollado emplea la Cromatografía Capilar Electrocinética Micelar, una modalidad de Electroforesis Capilar que ha permitido la cuantificación del metronidazol (MNZ), metronidazol-OH (MNZ-OH), dimetridazol (DMZ), ipronidazol (IPZ), dimetridazol-OH (HMMNI), ipronidazol-OH (IPZ-OH), ronidazol (RNZ), ornidazol (ORZ) y ternidazol (TRZ). Dicho método se ha aplicado a la determinación de residuos de estos compuestos en muestras de agua del río Genil (Granada).

Posted in 5-nitroimidazoles, Drugs, MEKC, SPE, Trabajo fin máster, UV-vis, Water | Comments Off on Desarrollo de un método MEKC para la determinación de 5-nitroimidazoles en aguas de río

Evaluación de la microextracción líquido-líquido dispersiva para la determinación de patulina en zumos de manzana mediante electroforesis capilar

Posted on 20 September, 2011 by fqm302

La contaminación microbiológica de los alimentos es la causa principal de las enfermedades de origen alimentario. Dentro de este tipo de contaminación destacan las micotoxinas, sustancias producidas por ciertos hongos pertenecientes principalmente a los
géneros Aspergillus, Fusarium y Penicillium. Estas sustancias suelen encontrarse en una gran variedad de productos agrícolas, almacenados en condiciones de humedad y aerobiosis, y son los contaminantes naturales de los alimentos más extendidos a nivel mundial. Se trata de productos altamente tóxicos, los cuales pueden producir mutaciones, cáncer, malformaciones en los fetos y disminuir la actividad del sistema inmune. Debido a su gran variedad de efectos tóxicos y, sobre todo, a su extrema resistencia al calor (termorresistencia), la presencia de las micotoxinas en los alimentos es considerada de alto riesgo para la salud humana y de los animales. La contaminación de los alimentos con micotoxinas es dependiente de las condiciones ambientales, que pueden propiciar el crecimiento del hongo y, por tanto, la producción de las toxinas. De este modo, la mayoría de los productos agrícolas pueden ser susceptibles de contaminación casi en cualquier momento, desde su producción en el campo, durante la cosecha, en el transporte y en el almacenamiento.

La patulina es una micotoxina producida por los hongos Penicillium griseofulvum (P. patulum o P. urticae) en cereales y nueces, P. expansum en manzanas y en gran variedad de frutas, P. gladioli y P. sclerotigenum en rizomas y bulbos. Estos hongos contaminan principalmente en la etapa de postcosecha de la fruta, ya que la mayoría de las especies productoras de patulina crecen a temperaturas de refrigeración. La patulina, al igual que las demás micotoxinas, puede ser neurotóxica, inmunotóxica, inmunosupresiva, genotóxica, teratogénica y carcinogénica. Como resultado, la legislación a nivel europeo sobre seguridad alimentaria es cada vez más restrictiva en cuanto a los niveles de patulina en alimentos y ha establecido los contenidos máximos de esta micotoxina mediante el Reglamento (CE) N º 1881/2006 [1]. Estos contenidos máximos se han establecido en 50 μg/kg para zumos de frutas, zumos de frutas concentrados reconstituidos y néctares de frutas, en 25 μg/kg para productos sólidos elaborados con manzanas, incluidos la compota y el puré de manzana destinados al consumo directo y, por último, en 10 μg/kg para zumo de manzana y productos sólidos elaborados a base de manzanas, incluidos la compota y el puré de manzana, destinados a los lactantes y niños de corta edad y para alimentos infantiles distintos de los alimentos elaborados a base de cereales lactantes y niños de corta edad.

Los métodos desarrollados para la determinación de patulina, habrán de presentar, por tanto, una adecuada selectividad, permitiendo efectuar análisis sin que interfieran los componentes de la matriz, así como una alta sensibilidad. De este modo, la etapa de tratamiento de muestra será, por tanto, decisiva en el diseño de tales métodos.

En los últimos años existe un creciente interés en la simplificación y miniaturización de los sistemas de tratamiento de muestra, introduciendo disolventes menos contaminantes y disminuyendo considerablemente los volúmenes utilizados, en línea con los principios de la llamada Química Verde o Química beneficiosa para el medio ambiente. Se trata de diseñar
productos y procesos químicos que reduzcan o eliminen el uso y producción de sustancias peligrosas, implicando una mayor seguridad y un menor coste en relación a los procesos convencionales. Así, la microextracción líquido-líquido (liquid phase microextraction, LPME) es una técnica simple y económica en la que se requieren sólo unos microlitros de disolvente para concentrar a los analitos a partir de las muestras, en lugar de los elevados volúmenes requeridos en la extracción líquido-líquido convencional.

Este trabajo tiene como objeto principal la puesta a punto de una metodología de tratamiento de muestra LPME recientemente desarrollada denominada microextracción líquido-líquido dispersiva (dispersive liquid phase microextraction, DLLME), previa al análisis de patulina en zumos de manzana, que presenta la ventaja de ser eficaz, rápida y sencilla, además de reducir el consumo de disolventes orgánicos. Para ello, se hará uso de la cromatografía capilar electrocinética micelar (micellar electrokinetic capillary chromatography, MEKC) con detección UV-VIS, como técnica de separación, dada la naturaleza de la molécula y las ventajas que presenta esta metodología frente a los métodos habituales basados en cromatografía líquida.

Posted in DLLME, Juice, MEKC, Mycotoxins, Trabajo fin máster, UV-vis | Tagged | Comments Off on Evaluación de la microextracción líquido-líquido dispersiva para la determinación de patulina en zumos de manzana mediante electroforesis capilar

Comparison of different sample treatments for the analysis of quinolones in milk by capillary-liquid chromatography with laser induced fluorescence detection

Posted on 5 July, 2011 by fqm302

A simple and very sensitive capillary-liquid chromatography method coupled with laser induced fluorescence detection has been developed for the simultaneous determination of seven quinolones of veterinary use in milk. Moreover, a comparison between two different sample treatments (QuEChERS and molecularly imprinted polymer, MIP) has been carried out in terms of efficiency of the extraction (number of analytes to be analysed and absence of interferences), throughput, linear dynamic range in matrix-matches calibrations, detection and quantification limits and accuracy (trueness and precision, by means of recovery assays). The results showed that the QuEChERS procedure was more efficient and faster, showing good recoveries, sensitivity and precision for all the studied compounds. Employing this proposed method, very low detection limits, between 0.4 μg/kg for danofloxacin, and 6 μg/kg for sarafloxacin, have been obtained.

Posted in Capillary HPLC, LIF, MIPs, Milk, QuEChERS, Quinolones | Tagged | Comments Off on Comparison of different sample treatments for the analysis of quinolones in milk by capillary-liquid chromatography with laser induced fluorescence detection

Use of dispersive liquid–liquid microextraction for the determination of carbamates in juice samples by sweeping-micellar electrokinetic chromatography

Posted on 25 April, 2011 by fqm302

Dispersive liquid–liquid microextraction (DLLME) has been proposed for the extraction and preconcentration 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.

Posted in Carbamates, DLLME, Electrophoresis, Juice, MEKC, Stacking, UV-vis | Tagged | Comments Off on Use of dispersive liquid–liquid microextraction for the determination of carbamates in juice samples by sweeping-micellar electrokinetic chromatography

Analytical applications of photoinduced chemiluminescence in flow systems—A review

Posted on 15 September, 2010 by fqm302

In this review, the recent evolution and the state of the art of photochemical reactions coupled with chemiluminescence processes are presented. Different chemiluminescence systems have been considered together with suitable photochemical derivatization processes that can affect either the analyte of interest or even the chemiluminogenic reagent, producing some derivatives able to participate more efficiently in the CL reactions and enhancing the CL emission. The on-line integration of the photochemical reactions as well as the coupling of this resulting photoinduced chemiluminescence (PICL) method with dynamic analytical systems, such as flow injection analysis, liquid or gas chromatography and capillary electrophoresis, have been discussed. Important applications of PICL have been proposed in environmental, pharmaceutical and food analysis.

Posted in Chemiluminescence, Photoinduced, Review | Tagged | Comments Off on Analytical applications of photoinduced chemiluminescence in flow systems—A review

Determination of Ocratoxin A by capillary HPLC with laser induced fluorescence detection

Posted on 6 July, 2010 by fqm302

In this abstract we propose the coupling of capillary-HPLC with LIF for the analysis of OTA, using anionic micellar medium in the mobile phase, which constitutes a very efficient alternative, increasing sensitivity and selectivity. To the best of our knowledge, this is the first time that this methodology is used for OTA detection.

Posted in Capillary HPLC, Chromatography, Fluorescence, LIF, Mycotoxins | Tagged | Comments Off on Determination of Ocratoxin A by capillary HPLC with laser induced fluorescence detection

On-line preconcentration for the determination of aflatoxins in rice samples by micellar electrokinetic capillary chromatography with laser induced fluorescence detection

Posted on 30 June, 2010 by fqm302

MEKC coupling with LIF detection has been used for the determination of four aflatoxins (B1, B2, G1 and G2). Separations were performed in an uncoated fused-silica capillary (70 cm×75 μm id, 55 cm effective length), using 20 mM borate buffer with 30 mM SDS (pH 8.5) and 7% ACN. In order to increase sensitivity, an on-line preconcentration procedure was applied, based on sweeping, using the same separation buffer without SDS as solvent of the sample. The precision of the method was evaluated in terms of repeatability and intermediate precision and the results were acceptable in all cases (RSD<12%). With the on-line preconcentration LODs (obtained as 3×S/N) were as low as 0.11, 0.52, 0.04 and 0.10 μg/L for G2, G1, B2 and B1, respectively. Recovery studies were developed with extracts of rice samples spiked with aflatoxins, being in the range between 93.0 and 105.4%. The method has also been applied to the determination of aflatoxins in rice samples, and the results compared with those obtained by a standard method, being in good agreement.

Posted in Fluorescence, LIF, MEKC, Mycotoxins, Rice, Stacking | Tagged | Comments Off on On-line preconcentration for the determination of aflatoxins in rice samples by micellar electrokinetic capillary chromatography with laser induced fluorescence detection

Advances and analytical applications in chemiluminescence coupled to capillary electrophoresis

Posted on 18 June, 2010 by fqm302

The present review presents the state of the art of the developments, key strategies and analytical applications of chemiluminescence detection coupled to CE (CE-CL). Different parts considering the most common CL systems have been included, such as the tris(2,2′-bipyridine)ruthenium(II) system, the luminol and derivatives reaction, the peroxyoxalate CL or direct oxidations. New advances in homemade configurations and applications in different fields such as clinical, pharmaceutical, environmental and food analysis have been included. The focus is on studies which appeared from 2000 to the end of 2009.

Posted in Chemiluminescence, Electrophoresis, Review | Tagged , | Comments Off on Advances and analytical applications in chemiluminescence coupled to capillary electrophoresis