M. L. Fernández-de Córdova

Investigation by ICP-MS of trace element levels in vegetable edible oils produced in Spain

The content of trace elements (Ag, As, Ba, Be, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Ti, Tl and V) in edible oils (virgin olive, olive, pomace-olive, sunflower, soybean and corn) from Spain was determined, using inductively-coupled plasma-mass spectrometry (ICP-MS) after microwave digestion, employing only nitric acid in this step. The method has been validated by using both an oil reference material and recovery experiments over different oil samples, obtaining satisfactory results in all cases. Inter-day repeatabilities lower than 10% were observed for all of the analysed elements in the different kinds of oil samples. Studying the content of trace elements, in order to detect tendencies in the samples of the same type of oil, principal components analysis was used. Promising groupings were observed using a model with two principal components and retaining 75.3% of the variance.

Lanthanide-Sensitized Luminescence as a Promising Tool in Clinical Analysis

Abstract The recent applications and novelties of lanthanide-sensitized luminescence (LSL) as a detection technique in clinical analysis are here reviewed. In LSL, lanthanide ions form complexes with organic compounds; in these complexes, the energy absorbed by the organic chromophore (usually the analyte) at its characteristic excitation wavelength is transferred to a triplet state of the molecule and then transferred to a resonance level of the lanthanide ion, which finally emits luminescence at its particular emission wavelength. The characteristics of this process will be reviewed and particular attention will be paid to the development of automatic methods of analysis, fluorescence probes, or flow-through optosensors, due to their potential applications in clinical analysis. A critical discussion of the advantages and handicaps of each analytical method is done and the trends of analytical chemistry in this research field are also presented.

A flow-through optosensing device with fluorimetric transduction for rapid and sensitive determination of dipyridamole in pharmaceuticals and human plasma

A flow-through optosensor with fluorimetric transduction has been prepared for the sensitive and selective determination of dipyridamole in aqueous solutions and biological fluids. The method is based on a monochannel flow-injection analysis system using Sephadex QAE A-25 resin, placed into a Hellma 176-QS fluorimetric flow-through cell, as an active sorbing substrate. The native fluorescence of dipyridamole fixed on the solid sorbent is continuously monitored at wavelengths of 305 and 490 nm for excitation and emission, respectively. After obtaining the maximum fluorescence intensity, the eluent solution (KH(2)PO(4)/NaOH buffer solution, c(T)=0.05 mol l(-1), pH 6.0) is allowed to reach the flow cell, the analyte is removed, and the resin support is regenerated. When an NaOH (10(-4) mol l(-1))/NaCl (0.1 mol l(-1)) solution is used as carrier solution, at a flow-rate of 1.56 ml min(-1), the sensor responds linearly in the measuring range of 10-500 microg l(-1) with a detection limit of 0.94 microg l(-1) and a throughput of 22 samples per hour (300 microl of sample volume). The relative standard deviation for ten independent determinations (200 microg l(-1)) is less than 0.82%. The method was satisfactorily applied to the determination of dipyridamole in pharmaceutical preparations and human plasma.

Solid-phase spectrophotometric determination of trace amounts of vanadium at sub-ng/ml level with 4-(2-pyridylazo)resorcinol.

Solid-phase spectrophotometry has been applied to analysis for trace amounts of vanadium. Vanadium was sorbed in a styrene-divinylbenzene-type anion-exchanger Dowex 1-X8 as a vanadium-4-(2-pyridylazo)resorcinol complex. Resin phase absorbances at 562 and 800 nm were measured directly which allowed the determination of vanadium in the range of 0.1-2.4 ng/ml with a RSD of 1.5%. The method has been applied to the determination of vanadium in different samples, namely toadstool tissue, mussel tissue, petroleum crudes and swamp water.

Integrated flow injection-solid phase spectrophotometric determination of minoxidil

A flow-through solid phase spectrophotometric (SPS) sensing device is proposed for the determination of minoxidil. The analyte is concentrated on Sephadex SP-C25 ion-exchanger packed in a flow cell and it is monitored by UV-Vis spectrophotometry at 282 nm, without derivatization reaction. When a HCl (10(-2) mol l(-1))/NaCl (5x10 (-2) mol l (-1)) solution is used as carrier/desorbing solution, the sensor responds linearly in the measuring range of 0.2-7, 0.1-4 and 0.05-2 mug ml(-1) with detection limits of 60, 33 and 6 ng ml(-1) for 600, 1000 and 2000 mul of sample, respectively. The relative standard deviations (%) for these volumes are 0.38, 1.06 and 2.63, respectively. The method was satisfactorily applied to the determination of minoxidil in pharmaceutical preparations and the results were compared with those obtained by high performance liquid chromatography (HPLC).

Fluorimetric determination of thiabendazole residues in mushrooms using sequential injection analysis

Thiabendazole is a benzimidazole fungicide of general use that is specifically used to control mushroom diseases, mainly cobweb diseases, which is caused by members of the genus Cladobotryum. Although this compound is legislated and its maximum residue limit established at 60mgkg(-1) by Codex Alimentarius, there is almost a complete absence of analytical methods available for its determination in mushrooms. Here, we propose an automated method, using Sequential Injection Analysis with fluorescence detection (λ(exc)/λ(em)=305/345nm) for the determination of thiabendazole in mushrooms. We have developed a flow-through optosensor using C(18) silica gel as solid support placed in the flow-cell where the determination is performed. This method presents a detection limit of 0.5mgkg(-1), and recovery experiments have been carried out in different kinds of mushrooms at levels below the legislated maximum residue limit, demonstrating that the proposed analytical method fulfils the requirements for its applications in quality control of mushrooms.

Direct Determination of Cefadroxil by Chemiluminescence Using a Multicommutated Flow-Through Sensor

ABSTRACT A selective and direct chemiluminescence method was developed for the determination of cefadroxil, a broad-spectrum antibiotic effective in gram-positive and gram-negative bacterial infections. The method involves the implementation of solid-phase spectroscopy in a multicommutated flow system. The solid support is placed in the flow-through cell, and the reaction between the oxidant reagent (permanganate) and cefadroxil takes place on the microbeads, so yielding the analytical signal. The system showed a linear dynamic range of 2.7–110 µM, with a detection limit of 0.8 µM and an RSD of 3.3% (n = 10). The analyte was satisfactorily determined in pharmaceutical preparations and human urine.

Development of a rapid and automatic optosensor for the determination of cromolyn in biological samples.

Disodium cromoglycate (SCG) is an anti-allergic drug, which is applied locally or inhaled. After administration, a very small portion of the drug is absorbed, being the most eliminated part unchanged in the urine and bile; therefore, its determination in urine is indicative of the dose absorbed. Here, the first spectroscopic method for the determination of SCG, making use of a sequential injection optosensor with terbium-sensitized luminescence detection, is described. The cationic resin Chelex-100 was used as solid support in the detection area. The measurements were made at 336/545 nm (lambda(ex)/lambda(em)) and the system was calibrated for two sample volumes, 150 and 800 microl, depending on the samples analyzed. A detection limit of 15 ng ml(-1) and a RSD lower than 2% (n=10) were observed using the highest sample volume. The proposed method does not use any organic solvent or surfactant, so being environmental friendly. The analyte was satisfactorily determined in pharmaceuticals and human urine, the latter being spiked at the concentrations found after the administration of the drug.

Determination of trace amounts of copper with 4-(2-pyridylazo)resorcinol by solid phase spectrophotometry

A determination method for traces of copper by Solid-Phase Spectrophotometry (SPS) has been developed. It is based on the fixation of copper(II) as 4-(2-pyridylazo)resorcinol complex on a styrene-divinylbenzene anion-exchange resin. The resin phase absorbances at 525 and 800 nm are measured directly, and the determination of copper (with a RSD of 1.8%) is possible in the range of 0.3–4.5 μg L−1. The method has been applied to the determination of copper in different samples, i.e. mushrooms, tea, drugs and waters.

Study of the quenching effect of quinolones over CdTe-quantum dots using sequential injection analysis and multicommutation.

The field of light-emitting nanoparticles has experienced an enormous development over the past two decades. The fluorescence of these nanometer-size crystalline particles, called quantum dots (QDs), can be both quenched and enhanced by different compounds. Since a high percentage of articles related to QDs are focused on theoretical studies, the development of analytical methods with real applications is an important step in order to progressively demonstrate the versatility of these particles. Moreover, taking into account that most of the QDs-based analytical methods are non-automated, the development of automated flow methodologies is still a field that presents an important analytical potential. With this purpose, two automatic methodologies, multicommutated flow injection analysis and sequential injection analysis, have been here applied to the analysis of quinolones in pharmaceutical formulations, making use of the quenching effect caused by the analytes over mercaptopropionic acid-capped CdTe QDs fluorescence. Both methodologies were compared in terms of versatility, sample throughput, sensitivity, etc., and applied to the determination of five quinolones in pharmaceutical preparations available in the Spanish Pharmacopoeia. The detection limits ranged between 26 and 50μmolL(-1), and Relative Standard Deviations lower than 3% were observed in all cases.