Miguel Ángel López

HPLC determination of ibuprofen, diclofenac and salicylic acid using hollow fiber-based liquid phase microextraction (HF-LPME).

This paper describes an extraction method using a polypropylene membrane supporting dihexyl ether (three-phase hollow fiber-based liquid phase microextraction (HF-LPME)) for the analysis of several pharmaceuticals (salicylic acid (SAC), ibuprofen (IBU) and diclofenac (DIC)) followed by a HPLC determination using a monolithic silica type HPLC column, that allows lower retention times than the usual packed columns with adequate resolution. Detection was realized by means of a coupled in series diode array (DAD) and fluorescence (FLD) detectors. HF-LPME is a relatively new technique employed in analytical chemistry for sample pretreatment which offers more selectivity and sensitivity than any traditional extraction technique. Detection limits by DAD are 12, 53 and 40 ng mL(-1) for salicylic acid, diclofenac and ibuprofen, respectively and by FLD 7 and 2 ng mL(-1) for salicylic acid, and ibuprofen. The method has been successfully applied to their direct determination in human urine and the results obtained demonstrated that could be also applied to the determination of the corresponding metabolites.

Electromembrane extraction (EME) and HPLC determination of non-steroidal anti-inflammatory drugs (NSAIDs) in wastewater samples.

In this paper, an electromembrane extraction (EME) combined with a HPLC procedure using diode array (DAD) and fluorescence detection (FLD) has been developed for the determination of six widely used non-steroidal anti-inflammatory drugs (NSAIDs): salicylic acid (SAC), ketorolac (KTR), ketoprofen (KTP), naproxen (NAX), diclofenac (DIC) and ibuprofen (IBU). The drugs were extracted from basic aqueous sample solutions, through a supported liquid membrane (SLM) consisting of 1-octanol impregnated in the walls of a S6/2 Accurel(®) polypropylene hollow fiber, and into a basic aqueous acceptor solution resent inside the lumen of the hollow fiber with a potential difference of 10 V applied over the SLM. Extractions that were carried out in 10 min using a potential of 10 V from pH 12 NaOH aqueous solutions shown concentration enrichments factors of 28-49 in a pH 12 NaOH aqueous acceptor solution. The proposed method was successfully applied to urban wastewaters. Excellent selectivity was demonstrated as no interfering peaks were detected. The procedure allows very low detection and quantitation limits of 0.0009-9.0 and 0.003-11.1 μg L(-1), respectively.

Hollow fiber-based liquid phase microextraction (HF-LPME) for a highly sensitive HPLC determination of sulfonamides and their main metabolites

In this paper, three phase-hollow fiber-based liquid phase microextraction (HF-LPME) combined with a HPLC procedure using diode array (DAD) and fluorescence detection (FLD) has been developed for the determination of four widely used sulfonamides: sulfadiazine, sulfamerazine, sulfamethazine, sulfamethoxazole and their main metabolites, the corresponding N(4)-acetyl derivatives: N(4)-acetyl-sulfadiazine, N(4)-acetyl-sulfamerazine, N(4)-acetyl-sulfamethazine, N(4)-acetyl-sulfamethoxazole. A Q3/2 Accurel KM polypropylene hollow fiber supporting 1-octanol was used between a 2 M Na(2)SO(4) aqueous solution (pH 4) as a donor phase and aqueous solution (pH 12) as an acceptor phase. The procedure allows very low detection and quantitation limits of 0.3-33 ng L(-1) and 0.9-100 ng L(-1), respectively. The proposed method was applied to the determination of the analytes in environmental water samples (surface, tap and wastewater).

Hollow fiber-based liquid phase microextraction (HF-LPME) as a new approach for the HPLC determination of fluoroquinolones in biological and environmental matrices

In this paper, a three phase hollow fiber-based liquid phase microextraction (HF-LPME) combined with a HPLC procedure using diode array (DAD) and fluorescence detection (FLD) has been developed for the determination of eight widely used fluoroquinolones: marbofloxacin (MRB), norfloxacin (NRF), ciprofloxacin (CPR), danofloxacin (DNF), enrofloxacin (ENR), gatifloxacin (GTF), grepafloxacin (GRP) and flumequine (FLM). A Q3/2 Accurel PP polypropylene hollow fiber supporting 1-octanol was used between a 2 M Na2SO4 aqueous solution (pH 7) as donor phase and aqueous solution (pH 12) as acceptor phase. The microextraction parameters were optimised from an experimental central composite design. The procedure allows very low detection and quantitation limits of 0.3-16 ng L(-1) and 1-50 ng L(-1), respectively. The proposed method was applied to the determination of the analytes in bovine urine and in environmental water samples (surface, tap and wastewater).

Electrochemical immunoassay using magnetic beads for the determination of zearalenone in baby food: an anticipated analytical tool for food safety.

In this work, electrochemical immunoassay involving magnetic beads to determine zearalenone in selected food samples has been developed. The immunoassay scheme has been based on a direct competitive immunoassay method in which antibody-coated magnetic beads were employed as the immobilisation support and horseradish peroxidase (HRP) was used as enzymatic label. Amperometric detection has been achieved through the addition of hydrogen peroxide substrate and hydroquinone as mediator. Analytical performance of the electrochemical immunoassay has been evaluated by analysis of maize certified reference material (CRM) and selected baby food samples. A detection limit (LOD) of 0.011 microg L(-1) and EC(50) 0.079 microg L(-1) were obtained allowing the assessment of the detection of zearalenone mycotoxin. In addition, an excellent accuracy with a high recovery yield ranging between 95 and 108% has been obtained. The analytical features have shown the proposed electrochemical immunoassay to be a very powerful and timely screening tool for the food safety scene.

Electrochemical microfluidic chips coupled to magnetic bead-based ELISA to control allowable levels of zearalenone in baby foods using simplified calibration

A novel analytical strategy that couples enzyme-linked immunosorbent assay (ELISA) and electrochemical microfluidic chips to determine the mycotoxin zearalenone (ZEA) in baby foods is presented. The analytical cycles for an ultra-fast analysis of the sample and its sequential fast and simplified calibration were performed in about 200 s plus to ELISA protocol. This route avoided the typical four-parameter logistic curve fit which is a highly time-consuming and laborious procedure. An extremely low concentration level of ZEA (less than 1 ppb) was detected with reliability. This level is 20 times lower than the strictest tolerable limit (20 ppb) for baby foods, making the microfluidic approach the newly anticipated analytical security tool for the future. The reliability of the proposal was demonstrated by accuracy evaluations using a certified reference material and by demonstrating its suitability during the control of the regulatory limits of ZEA in baby foods. In addition, the microfluidic approach allowed sensitivity and the incubation enzymatic reaction to be manipulated in situ.

Simplified calibration and analysis on screen-printed disposable platforms for electrochemical magnetic bead-based inmunosensing of zearalenone in baby food samples

An electrochemical immunosensor involving magnetic beads and disposable carbon screen-printed electrodes (SPEs) for zearalenone (Zea) sensing has been developed and evaluated using a certified reference material (CRM) and selected baby food samples. After the immunochemical reaction, the modified paramagnetic beads were confined by a magnet on surface of SPE platforms where electrochemical detection is simply achieved through the suitable substrate and mediator for the HRP enzyme. A remarkable detection limit of 0.007 microg L(-1) and excellent accuracy with recovery rate of 101-111% showed the proposed system to be a very suitable screening tool for the analysis of zearalenone in baby food samples. A new simple, fast and reliable strategy involving the sequential performing of calibration and analysis of target mycotoxin using just one disposable SPE each is additionally proposed. Excellent analytical performance in terms of accuracy and precision were again obtained with a remarkable low systematic error (less than 4%) and excellent reproducibility (RSD=6%). This strategy enhanced the analytical merits of immunosensor approach towards truly analytical disposable tools for food-safety scene.

Enzyme-based microfluidic chip coupled to graphene electrodes for the detection of D-amino acid enantiomer-biomarkers.

An electrochemical microfluidic strategy for the separation and enantiomeric detection of D-methionine (D-Met) and D-leucine (D-Leu) is presented. These D-amino acids (D-AAs) act as biomarkers involved in relevant diseases caused by Vibrio cholerae. On a single layout microfluidic chip (MC), highly compatible with extremely low biological sample consumption, the strategy allowed the controlled microfluidic D-AA separation and the specific reaction between D-amino acid oxidase (DAAO) and each D-AA biomarker avoiding the use of additives (i.e., cyclodextrins) for enantiomeric separation as well as any covalent immobilization of the enzyme into the wall channels or on the electrode surface such as in the biosensor-based approaches. Hybrid polymer/graphene-based electrodes were end-channel coupled to the microfluidic system to improve the analytical performance. D-Met and D-Leu were successfully detected becoming this proof-of-the-concept a promising principle for the development of point-of-care (POC) devices for in situ screening of V. cholerae related diseases.

Multidimensional carbon allotropes as electrochemical detectors in capillary and microchip electrophoresis.

The main multidimensional carbon allotropes could be classified into carbon nanotubes as 1D material, graphene as 2D material, as well as graphite and diamond as 3D carbon materials. Along with this review, a discussion using these four structures as electrochemical detectors in CE and ME will permit us to explore the recent advances in this field.

The fractal dimension of stone pore surface as weathering descriptor

Pore surface fractal dimension of building stones were measured using mercury porosimetry in a pore diameter range from 100 to 0.012 μm. Surface fractal dimension can be used as descriptor of the stone pore surface, allowing an easier differentiation between weathered and unweathered stone than the pore size distribution. For the studied materials, weathering processes cause an increase in the surface fractal dimension.