Jesús R. Procopio

Study of fractionation and potential mobility of metal in sludge from pyrite mining and affected river sediments: changes in mobility over time and use of artificial ageing as a tool in environmental impact assessment.

Sludge from mining exploitation can be a source of land and water contamination in the adjacent zone. Accidents such as the break of waste mining pools in the Aznalcollar Mine (Seville, Spain) in 1998 produce important ecological disasters. In this work is presented a study of the evolution of aqua regia leachable concentration and mobility of metals in sediment samples of Guadiamar River basin from the accident date up to 2001. The application of BCR standard extraction procedures provides valuable information about the mobility and toxicity of the spill and the metal mobility in Guadiamar River polluted sediments. As a rule, themobility of several metals in the initial sludge (sulphides) is low, except for copper. Otherwise, the results of aqua regia leachable concentration and mobility of metal obtained for sediments samples indicate that the cleaning and inertisation works carried out in the zone have been adequate but insufficient, being the metal levels observed in the zone are higher than natural levels. To establish the initial impact of the spill and the mobility changes with time, mineralogical composition of the pyritic sludge and its evolution after the natural weathering and after the induction, of accelerated ageing processes by light and temperature was studied in the laboratory. Oxidation of initial sulphides to sulphates was observed. Both environmental and laboratory oxidation of the metallic sulphides increase the mobility of all metals, especially of copper, zinc and lead. The proposed laboratory procedure allows to predict the changes in mobility and therefore in toxicity that can occur at short or long term after exposure of sludge at environ-mental conditions. The mobility results in sludge and sediment samples are interpreted in terms of the mineral composition of the samples.

Sensitive and selective determination of phenolic compounds from aromatic plants using an electrochemical detection coupled with HPLC method.

INTRODUCTION Phenolic compounds contained in essential oils from plants are responsible for their anti-oxidant capacity. The natural extract from each aromatic plant is characterised by a typical ratio of phenolic components, so each one of the essential oils shows different properties. OBJECTIVE The development of a simple reversed-phase high-performance liquid chromatographic (RP-HPLC) method for the determination of phenolic compounds from aromatic plants using spectrophotometric detection with a diode-array and electrochemical detection with amperometric and coulometric detectors. METHODS Chromatographic conditions are optimised to separate vanillin, eugenol, thymol and carvacrol using spectrophotometric detection. Acetonitrile and methanol are studied as mobile-phase organic modifiers. The hydrodynamic curves are obtained for both electrochemical detection modes and the principal values of merit are calculated. The proposed methodology is applied to determine the four analytes in real samples. RESULTS The shortest elution times and the highest electrochemical signals are achieved using 65% methanol solution in 0.1 mol/L acetic acid-acetate buffer as the mobile phase. Potential values of 0.925 V for amperometric detection and 0.500 V for coulometric detection are chosen as working potentials. The limits of detection (LOD) for the compounds studied ranged between 9.7-17 µg/L and 0.81-3.1 µg/L in amperometric and coulometric detection modes, respectively. In general, the obtained LODs are better than those previously reported. CONCLUSION The low LODs obtained using coulometric detection make this methodology very competitive and adequate for quality control of these phenolic compounds in comparison with others, such as GC-MS, that are more expensive and complicated to use than the RP-HPLC method with coulometric detection.

Reversed-phase high-performance liquid chromatography of pyrrolidinedithiocarbamate complexes of mercuric species using amperometric and coulometric detection

Abstract A reversed-phase high-performance liquid chromatographic method has been developed for the determination of organic and inorganic mercury species as pyrrolidinedithiocarbamic complexes using electrochemical detection. These complexes were prepared off-line and separated using as mobile phase a mixture of methanol-water (75:25) containing KNO 3 as supporting electrolyte. The organomercury complexes were detected in both amperometric and coulometric mode, at + 1.15 V and + 0.90 V respectively. The detection limits ranged from 0.16 ng to 2.8 ng.

HPLC analysis of thimerosal and its degradation products in ophthalmic solutions with electrochemical detection.

A reverse-phase high-performance liquid chromatographic assay using amperometric detection on a glassy-carbon electrode has been developed for analysis of thimerosal and its main degradation products, thiosalicylic acid and dithiodibenzoic acid, in ophthalmic formulations. A potential value of 0.9 V vs. Ag/AgCl was chosen for simultaneous detection of thimerosal and thiosalicylic acid, obtaining limits of detection of 1.0 and 0.2 ng injected, respectively. A potential value of 1.2V was applied for simultaneous determination of all three compounds studied, obtaining in this case limits of detection of 3,4 and 4 ng injected for thimerosal, thiosalicylic acid and dithiodibenzoic acid, respectively. The results obtained reveal the utility of the HPLC method in quality control of commercial products containing thimerosal with good detectability.

Spectrofluorimetric determination of 1,4-thienodiazepines

Abstract The fluorescence characteristics of four 1,4-thienodiazepines in aqueous and methanolic solutions and the effect of pH on fluorescence intensity are described. The p K a values are calculated. Fluorimetric methods with limits of detection between 3 and 38 ng ml −1 were developed, and applied for determinations of one drug in tablets, and the others in serum after extraction with a Sep-Pak C 18 cartridge.

Determination of clotiazepam by HPLC with spectrophotometric and amperometric detection

SummarySpectrophotometric and amperometric detectors were compared for the determination of clotiazepam by HPLC. Methanol-water (60∶40) containing 0.01 mol/l ammonium acetate and methanol-water (70∶30) containing 0.01 mol/l acetate buffer pH 4 were used as mobile phase in the spectrophotometric and amperometric detection, respectively. The minimum detectability for the spectrophotometric detection was 20 ng injected and the method was applied for the determination of clotiazepam in serum, whereas for the amperometric detection a limit of detection of 2.5 νg injected was obtained, using this technique for clotizepam determination in tablets.

Evaluation of the capability of different chromatographic systems for the monitoring of thimerosal and its degradation products by high-performance liquid chromatography with amperometric detection

Several liquid chromatographic systems using electrochemical detection on carbon electrodes were compared for the analysis of thimerosal and its degradation products, thiosalicylic acid and dithiodibenzoic acid. The studied separation systems included reversed-phase ion-suppressed chromatography, reversed-phase ion-pair chromatography and ion chromatography. Amperometry and coulometry were evaluated as electrochemical detection techniques. The best method for thimerosal determination in ophthalmic solutions in terms of selectivity and sensitivity was ion-pair chromatography.

Determination of 1,4-thienodiazepines by liquid chromatography with spectrophotometric, amperometric and coulometric detection

Spectrophotometric, amperometric and coulometric methods of detection for the liquid chromatographic determination of four 1,4-thienodiazepines were compared. The effects of several experimental parameters on the separation and sensitivity of the method was evaluated. A mobile phase consisting of methanol—water (60 + 40) and containing ammonium acetate buffer (pH 7) appeared to be optimal when using a 4-μm Novapak ODS column. The amperometric and coulometric detectors, equipped with glassy carbon electrodes, were operated at +1.05 V vs. Ag/AgCl. The limits of detection obtained ranged from 0.05 to 0.2 μg ml−1 for spectrophotometric detection, from 0.05 to 0.2 μg ml−1 for amperometric detection and from 0.006 to 0.02 μg ml−1 for coulometric detection.

Determination of thiolcarbamate herbicides in natural water by HPLC with spectrophotometric detection

SummaryThiolcarbamates used for killing weed seeds were determined in natural waters by HPLC with spectrophotometric detector. Methanol-water (80:20) containing 0.01 mol/l ammonium acetate buffer pH 5.0 was used as mobile phase. The column was thermostated at 35°C. Seppak C18 cartridges were used for sample preparation and preconcentration. The minimum detectable concentration for samples of 100 ml was 0.5 ng/ml.