Zuriñe Gomez de Balugera

Determination of imidacloprid and its major metabolite in soils by liquid chromatography with pulsed reductive amperometric detection

Abstract A liquid chromatography method assay for imidacloprid insecticide and its major metabolite 6-chloronicotinic acid was developed to monitor both compounds in soils. The electrochemical study of the compounds proves the reduction and adsorption processes on the mercury electrodes. Pulsed amperometric detection overcomes electrode fouling problems by repeatedly and continuously applying cleaning potentials to the working electrode. The measurement potential was −1300 mV and the cleaning and conditioning potentials were −500 and −1150 mV, respectively. The Chromatographic separation was achieved on a Spherisorb CN column 5 μm (4.1 × 250 mm). Samples were eluted with a mobile phase containing 5 × 10 −3 M phosphate buffer-acetonitrile (75 : 25), pH 2.5 at a flow rate of 1.0 ml min −1 . The limit of detection for this method was 2.7 ng of imidacloprid and 8.1 ng of 6-chloronicotinic acid.

Electrochemical study of the flavour enhancer maltol. Determination in foods by liquid chromatography with amperometric detection

Abstract The electrochemical behaviour of maltol on a glassy carbon electrode was studied. The results were applied to electrochemical detection in liquid chromatography (LC-ED). Liquid chromatography (LC) and oxidative amperometric detection with a glassy carbon electrode were used for the determination of maltol in food samples. A mobile phase of methanol-acetonitrile-citrate/phosphate buffer, pH = 2.4 (50:48:2) was used with the detector operated at E = 1000mV vs. Ag AgCl reference electrode. Under optimal conditions detection and determination limits of 0.1 and 3.7 ng respectively were obtained. The method was used for the determination of maltol in cakes. Conditions for clean-up of the sample were established using solid phase extraction cartridges.

Utilization of a silica-modified carbon paste electrode for the direct determination of todralazine in biological fluids

Todralazine [ethyl 2-(-1-phthalazinyl)hydrazinecarboYylate] was determined by using a carbon paste electrode modified with silica. Todralazine is adsorbed on the electrode and determined in 0.1 mol l -1 KNO 3 (pH 1.8) by differential-pulse voltammetry. The adsorption can be carried out in open circuit or by applying a fixed potential (0.8 V vs. Ag/AgCl). The detection limits are about 4×10 -7 and 3×10 -8 mol l -1 , respectively. The method can be applied to the determination of todralazine in human urine

Joint determination of todralazine and acetazolamide in human serum by differential pulse polarography

Differential pulse polarography (DPP) is proposed as a direct method for the quantitation of todralazine and acetazolamide in human serum. The method was applied to the determination of these drugs in human serum, after a liquid-liquid extraction process. This extraction process together with the use of the standard additions method is essential for the elimination of the matrix effect. The proposed method enables detection limits of 0.107 microgram ml-1 for acetazolamide and 0.111 microgram ml-1 for todralazine to be achieved at reduction potentials of -0.59 and -0.86 V, respectively, using Britton-Robinson buffer (pH 1.65) as the supporting electrolyte.

Evaluation of amperometric detection at a glassy carbon electrode for the liquid-chromatographic determination of antihypertensive substances

A liquid chromatographic technique with amperometric detection has been developed for determining the antihypertensive drugs captopril, todralazine and prazosin in human serum samples. The technique is based on the oxidation possibilities of these compounds at glassy carbon electrodes. An individual electrochemical study of the three compounds has been carried out and the solution and instrumental variables, such as joint oxidation potential, pH, and buffer and mobile-phase compositions, have been optimized. The internal standard selected was timolol, a beta-blocker drug with antihypertensive effects that has similar groups, that can be oxidized at a glassy carbon electrode. Conditions for the prior extraction of the three substances from serum have been established using solid–liquid extraction cartridges. The technique proposed permits the simultaneous determination of trace amounts of captopril, todralazine and prazosin in human serum samples, with detection limits of 0.20, 0.004 and 0.06 µg ml–1, respectively, and recoveries of 95.8, 99.8 and 98.7%.

Determination of the insecticide pyridafenthion in river water, soils and wine by adsorptive stripping voltammetry.

Solid-phase extraction or liquid-liquid extraction has been combined with adsorptive stripping voltammetry at a hanging mercury drop electrode to isolate, determine, quantify and recover trace concentrations of pyridafenthion in water, wine and soil. A systematic study of the experimental parameters affecting the stripping response was carried out by differential pulse voltammetry. By using an accumulation potential of 400 mV and an accumulation time of 540 s, the limit of detection was 0.17 microgram l-1 and the relative standard deviation (n = 10) was 1.9% at a concentration level of 8.5 micrograms l-1. Different methods are proposed which eliminate matrix interferences. These results have been applied to the systematic study of this compound in water, wine and soil. The lowest detectable concentration for pyridafenthion is 34 micrograms l-1 in water, 102 micrograms l-1 in wine and 80 micrograms kg-1 in soil. Recoveries of the pyridafenthion from supplied environmental samples were in all cases higher than 92% with a relative standard deviation lower than 3%.

Determination of N-nitrosopiperidine in beers by liquid chromatography with reductive amperometric detection at a hanging mercury drop electrode

Abstract Liquid chromatographic separation prior to reductive electrochemical determination at the hanging mercury drop electrode is used to determine N -nitrosopiperidine (NPIP). A mobile phase of methanol-acetonitrile-phosphate buffer, pH 3.5 (57:38:5) is used with the detector operated in the direct current (DC) mode at E p = −1250 mV . Techniques for oxygen removal and electrochemical considerations are presented. The detection limit is 0.2 ng injected with a relative standard deviation ( n = 10) of 2.8%. The method can be applied to the determination of NPIP in beers. Conditions for the prior extraction of NPIP from beer samples have been established using solid phase extraction cartridges.

Voltammetric method for the determination of the flavour enhancer inosinic acid

An adsorptive stripping voltammetric–differential-pulse reversible (AdSV–DPR) method for the determination of inosinic acid is described. Inosinic acid or its metabolite hypoxantine is adsorbed on a hanging mercury drop electrode (HMDE) and determined in Britton–Robinson buffer (pH 1.8) by DPR voltammetry. The hypoxanthine determination has sensitivity levels higher than those of inosinic acid, which is why the proposed method is based on hypoxanthine determination. The hydrolysis and extraction procedure was optimized using the standard additions method in the quantification step. The detection and determination limits of the technique are 8 × 10–9 and 3 × 10–8 mol l–1, respectively. The technique was applied to the determination of inosinic acid in dehydrated soup samples. The reproducibility of the method expressed by the relative standard deviation is 0.95%. The method is suitable for samples containing between 0.5 and 100 mg g–1 of inosinic acid.

Persistence of Diflubenzuron on Conifer Forest Foliage in a Mediterranean-Climate Ecosystem Following Aerial Application

Dimilin 45 ODC (diflubenzuron) was applied in a Mediterranean-climate conifer forest, near Vitoria, Basque Country, Spain. Pine needles were collected at post-treatment 5-day intervals for analysis of the diflubenzuron residues. A liquid chromatography method with on-line diode-array and electrochemical detection was developed for the determination of the pesticide diflubenzuron and its main metabolites: 2,6-diflurobenzamide, 4-chlorophenylurea, 4-chloroacetanilide, 4-chloroaniline and N-methyl-4-chloroaniline in forestry matrices. Aerial application at 56.3 g AI ha−1 resulted in deposition levels of the insecticide of 1080 ng g−1. Within 40-65 days following treatment, 51-73% of the insecticide had been removed from the foliage. During this period, the concentration of diflubenzuron was higher than 295 ng g−1. The only metabolite detected was 2,6-difluorobenzamide and this persisted on foliage until the first rainfalls occurred. An empirical mathematical correlation was found to express the influence of rainfall, solar radiation and temperature on the persistence of the insecticide.

Multisorbent tubes sampling used in thermal desorption cold trap injection with gas chromatography-mass spectrometry for C2–C6 hydrocarbon measurements in an urban atmosphere

Three solid adsorbents (Carbotrap, Carbotrap C, and Carbosieve III) were evaluated for sampling trace non-methane hydrocarbons in urban atmospheres. The sampled atmosphere was pumped through a multisorbent tube containing the three sorbents separated by a small amount of silanized glass wool. The trapped compounds were recovered by thermal desorption and analysed by combining cryogenic enrichment with gas chromatography and mass spectrometry. Adsorption/thermal desorption and breakthrough experiments were performed to test their ability to quantitatively trap the light hydrocarbons. The technique was suitable for determination of low ppbv concentrations of these compounds. Ambient atmospheric sampling was conducted in Vitoria-Gasteiz (Basque Country, Spain), and the measurements cover a period of one year (2001–2002). Fifteen C2–C6 hydrocarbons are identified and quantified, and seasonal trends are discussed.