Browsing by Issue Date, starting with "2010-02-18"
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- Application of bismuth modified disposable screen printed carbon electrode for metal- plant thiols complexation studiesPublication . Feyssa, Belachew Tolla; Diaz-Cruz, Jose ManuelThe application of Bismuth modified cheap and disposable screen printed carbon electrode (BiSPCE) for voltammetric studies of metal–thiol rich peptides complexation was evaluated considering systems consisting of cadmium as a metal and GSH and PC2 as thiol peptides. Comparison of the performance of BiSPCE with the commonly used glassy carbon electrode (BiFE) was made. The information obtained about the complexation sequence using the former electrode was quite consistent with previous studies made on GSH and Cd systems using the conventional mercury electrodes due to the absence of signal splitting, the good sensitivity and the wider linearity range. In contrast with the conventional mercury electrodes, the anodic signals associated with bismuth electrode material were observed to be weakened and all the available signals were well resolved which shows the suitability of Bismuth based electrode for metal- thiol complexation studies. MCR-ALS could not be applied due to the continuous shift of the peak potentials, loss of linearity of the species and anomalous shape of the complex signal formed between Cd and GSH. Therefore, the complexation sequence between GSH and Cd2+ was evaluated qualitatively. However, a relatively well defined shape and intense voltammograms were observed for Cd-PC2 system and consequently, MCR-ALS was applied after correction of the continuous peak potential shift for the complex signals. The peak intensity associated with complex signal was dominated by the intense signal of the free metal reduction in acidic and fairly basic medium. However a relatively intense signal of the complexes was obtained at pH 7.5 in borate buffer solution. In addition extensive Bi complexation was observed from ESI-MS experiment which proves the suitability of ex situ mode of Bi film preparation for thiol- metal complexation studies by voltammetric titration technique.
- Optimization of an SPE clean-up approach for the analysis of sulfonamides in animal feedPublication . Kumar, Praveen Kumar; Companyó, Ramon; Cavaco, Isabel Maria Palma Antunes ,In this work, clean up strategy is optimized for an analytical method based on liquid chromatography with UV detection for determination of eight sulfonamides (sulfachloropyridazine, sulfadiazine, sulfadimidine, sulfadoxine, sulfamethoxypyridazine, sulfaquinoxaline, sulfamethoxazole and sulfadimethoxine) in pig feed. Solid Phase Extraction is used for clean up and the performance of different sorbents - C 18, Oasis HLB, Plexa and Plexa PCX is assessed by their clean up efficiency and recovery of analytes. Oasis HLB and Plexa PCX sorbents provide better clean up and recovery values than C18 and Plexa. A spiked feed of 2 mg/kg is used to assess mean recoveries and precision in terms of repeatability, r and within-lab reproducibility, R for the whole method with Oasis HLB and Plexa PCX. Recoveries using Oasis HLB ranges from 51 to 78%, with RSDr from 5 to 15% and RSDR from 5 to 18%. Recoveries using Plexa PCX ranges from 64 to 85% with RSDr from 4 to 11% and RSDR from 7 to 17%..
- Multi-class, multi residue method for determination of penicillins, cephalosporins and quinolones in cow milk and validation in accordance with Commission Decision 2002/657/E CPublication . Amatya, Rameshwari; Torralbo, José Barbosa; Bueno, Dolores Barrón; Cavaco, Isabel Maria Palma AntunesThe method was developed to determine simultaneously 19 drugs of three classes (seven Penicillins and Cephalosporins, and five Quinolones) regulated by European legislation 2377/90/EC in cow milk using LC-MS/MS. To make the sample preparation as simple as possible deproteinization step using organic solvent was eliminated. SPE clean up and concentration was done using OASIS HLB cartridge. The separation of 19 antibiotics was achieved in 11 minutes using C8 column with gradient elution. MS data was acquired on MRM mode with two transitions for each compound. Validation procedure was conducted based on European directive 2002/657/EC. 89% of drugs presented recoveries higher than 65 % with exception of AMOX (57%) and DAN (38 %). Repeatability values expressed as relative standard deviation, (RSDs) were not more than 15 %. LODs values ranged from 0.03 (NAFC) to 0.5 μg/kg (PER) and LOQs from 0.1 (NAFC, PENG, CIP, DAN, and ENR) to 1.25 μg/kg (PER). The method was applied to 49 real samples. 37% of the sample was found to be non-compliant with an error probability of . Of all samples analysed, 14 % of samples contained AMOX and 16 % contained PENG. AMOX and PENG was the most common residue found in milk sample.
- Application of surface plasmon resonance and spectroscopic techniques for characterizing the interaction between human c-KIT G-quadruplex DNA and water soluble porphyrinsPublication . Shenkutie, Sintayehu Manaye; Gomez, Raimundo GargalloG-quadruplex DNA structures are hypothesized to be involved in regulation of telomere homeostasis and gene expression.
- Determination of temperature effecton the measurements of pKa of some weak acids and weak bases using capillary zone electrophoresisPublication . Gravador, Rufielyn Sungcaya; Pascual, Martí Rosés; Cavaco, Isabel Maria Palma AntunesThis study was done to determine the pKa values of a number of weak acidic and basic compounds at different temperatures and to be able to identify the effects of temperature variations in the measured pKa using capillary zone electrophoresis. The method employed was adopted from Fuguet et al [12] in which internal standard is used. Running buffers of different pH were prepared. The maximum voltage was chosen based from Ohm’s law to reduce the Joule heating effects. Considering the linearity in the relationship between voltage and current to be with an r2≥0.999, the maximum voltage was found to be 18 kV and applied to the determination of pKa values of several compounds at 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, and 50°C. For the determination of the pKa values of the analytes using internal standards with comparable pKa values at different temperatures, generally the calculated values did not vary significantly from the literature values under all the observed temperatures. For the investigation of the effects of temperature changes during the measurement of the pKa of the analyte at a specific temperature, internal standard with ΔH similar or different with the analyte was utilized. Results showed a small difference between the literature and experimental pKa values of the analyte at a specified temperature despite the temperature variations in the instrument when the internal standard and analyte have similar ΔH, which follows that in this case temperature control is not critical.
- Speciation of mercury in environmental samplesPublication . Ruiz , Wilder Leonardo Gamboa; Estrugo, Angels SahuquilloMercury is one of the most toxic elements impacting on human and ecosystem health and therefore is one of the most studied environmental pollutants. All mercury species are toxic, with organic mercury compounds generally being more toxic than inorganic species. For this reason, the assessment of mercury distribution in environmental samples is a key task in analytical chemistry. Reverse phase chromatography (RPC) coupled to a UV post-column oxidation system and vapor generation atomic fluorescence spectrometry was optimised for the speciation and determination of inorganic and organic mercury (methylmercury and ethylmercury) in the form of APDC complexes. The mercury-APDC complexes were separated on a reverse phase column and oxidized on-line with a UV source. Hg2+ was selectively detected by AFS after reduction with stannous chloride to Hg0. The mobile phase composition was modified to include the simultaneous detection of EtHg+ by optimising the MeOH – Water to a 75:25 ratio. Quality parameters for the analytical method were established and a short-term stability study for EtHg+ was undertaken. Investigations are described to select the most suitable pre-treatment procedure for mercury speciation in polluted sediment samples. Five different pre-treatment procedures were evaluated: freezing at -80 and -20 °C, air drying, oven-drying at 40 °C, and lyophilization. Total mercury determination was performed with an aqua regia extraction, while for mercury speciation a method formerly optimized for the speciation of Hg2+ and MeHg+ was used in the analysis of sediments. The chromatogfraphic system consists on a reverse phase column (C18), with a mobile phase composed of (80:20) MeOH – water containing APDC 0,0015M as complexing agent and HN4Ac 0,01M at pH 5,5. For total mercury measurement, best results were obtained when the sediments were dried (air dried, oven-dried or lyophilized) because frozen samples showed lower concentration of total mercury. In the case of speciation analysis, MeHg+ was not detected in the sediment samples. Significant differences were found in the Hg2+ concentration among the samples subjected to the studied pre-treatments, even if there is no evidence suggesting that one pre-treatment preserves better the original speciation information was found.