Carlos Bendicho

Chemical sequential extraction for metal partitioning in environmental solid samples.

A comprehensive review of the sequential extraction schemes for metal fractionation in environmental samples (ie., sediment, soil, sewage sludge, fly ash, etc.) is presented. The review contains more than 400 references and covers principally the literature published over the last decade. The use of each reagent involved in these schemes is looked at critically, and guidelines for their selectivity and extraction capacity are given. The operational character of these schemes is emphasised. Topics such as comparability between sequential extraction schemes of widespread use, harmonisation, acceleration, validation, etc. are addressed and future developments outlined.

Solid sampling in electrothermal atomic absorption spectrometry using commercial atomizers. A review

3 Slurry Sample Introduction 3.1 Preparation and Mixing of Slurries 3.1.1 Use of stabilizing agents 3.1.2 Magnetic stirring and vortex mixing 3.1.3 Ultrasonic agitation 3.1.4 Gas mixing of slurry 3.1.5 Pre-digestion of slurry 3.1.6 Electric dispersion in a condensed medium 3.2 Influence of Particle Size 3.3 Influence of Slurry Concentration 3.4 Chemical Modification 3.5 Calibration 3.6 Applications of Slurry Sample Introduction

Comparison of ultrasound-assisted extraction and microwave-assisted digestion for determination of magnesium, manganese and zinc in plant samples by flame atomic absorption spectrometry

In this paper, a sample preparation method based on acid extraction of magnesium, manganese and zinc from plant tissue by means of high intensity probe ultrasonication is described. Acid extracts obtained upon sonication were directly nebulised into an air-acetylene flame for fast metal determination by atomic absorption spectrometry. Parameters influencing extraction such as sonication time, ultrasound amplitude, sample mass, particle size, extractant composition and volume were fully optimised. Optimum conditions for metal extraction were as follows: a 3-min sonication time, a 30% ultrasonic amplitude, a 0.1-g sample mass, a particle size less than 50 mum, a 0.3% m/v HCl concentration in the extractant solution and a 5-ml extractant volume. Six plant samples used in the human diet were analysed, the concentration range of the three metals approximately being in the range of 1500-3000 mug g(-1) for Mg, 30-735 mug g(-1) for Mn and 20-45 mug g(-1) for Zn. Limits of detection corresponding to the ultrasound-assisted extraction method were 0.10, 1.26 and 0.65 mug g(-1) for Mg, Mn and Zn, respectively. Between-batch precision, expressed as R.S.D., was about 0.5, 1.5 and 1% for Mg, Mn and Zn, respectively. Analytical results for the three metals by ultrasound-assisted extraction and microwave-assisted digestion showed a good agreement, thus indicating the possibility of using mild conditions for sample preparation instead of intensive treatments inherent with the digestion method. The advantages and drawbacks of ultrasound-assisted extraction in respect to the microwave-assisted digestion are discussed.

Speciation of mercury by ionic liquid-based single-drop microextraction combined with high-performance liquid chromatography-photodiode array detection.

Room temperature ionic liquids can be considered as environmentally benign solvents with unique physicochemical properties. Ionic liquids can be used as extractant phases in SDME, being compatible with chromatographic systems. A single-drop microextraction method was developed for separation and preconcentration of mercury species (MeHg(+), EtHg(+), PhHg(+) and Hg(2+)), which relies on the formation of the corresponding dithizonates and microextraction of these neutral chelates onto a microdrop of an ionic liquid. Afterwards, the separation and determination were carried out by high-performance liquid chromatography with a photodiode array detector. Variables affecting the formation and extraction of mercury dithizonates were optimized. The optimum conditions found were: microextraction time, 20 min; stirring rate, 900 rpm; pH, 11; ionic liquid type, 1-hexyl-3-methylimidazolium hexafluorophosphate ([C(6)MIM][PF(6)]); drop volume, 4 microL; and no sodium chloride addition. Limits of detection were between 1.0 and 22.8 microg L(-1) for the four species of mercury, while the repeatability of the method, expressed as relative standard deviation, was between 3.7 and 11.6% (n=8). The method was finally applied to the determination of mercury species in different water samples.

Speeding up of a three-stage sequential extraction method for metal speciation using focused ultrasound

The three-stage sequential extraction procedure, proposed by the European Community Bureau of Reference (BCR), has been applied for speciation of copper, chromium, nickel, lead and zinc in a sludge sample collected from an urban wastewater treatment plant. The conventional BCR sequential extraction method has been modified, in each stage, applying ultrasonic energy by means of a probe (handling at an adequate sonication power and time) in order to shorten the required operation time. Extractable metal contents obtained by both the conventional and the accelerated ultrasonic extraction method, were measured by Flame-Atomic Absorption Spectrometry. Results obtained in each fraction by both methods were statistically compared (P=0.95) for all the studied elements and no significant differences were found except for chromium and zinc in the third fraction (oxidisable). For all metals the extraction percentage was>95%. The proposed accelerated sequential extraction method could be a valid alternative to the conventional shaking with a much shorter operating time.

Liquid-phase microextraction approaches combined with atomic detection: a critical review.

Liquid-phase microextraction (LPME) displays unique characteristics such as excellent preconcentration capability, simplicity, low cost, sample cleanup and integration of steps. Even though LPME approaches have the potential to be combined with almost every analytical technique, their use in combination with atomic detection techniques has not been exploited until recently. A comprehensive review dealing with the applications of liquid-phase microextraction combined with atomic detection techniques is presented. Theoretical features, possible strategies for these combinations as well as the effect of key experimental parameters influencing method development are addressed. Finally, a critical comparison of the different LPME approaches in terms of enrichment factors achieved, extraction efficiency, precision, selectivity and simplicity of operation is provided.

Hydride generation-headspace single-drop microextraction-electrothermal atomic absorption spectrometry method for determination of selenium in waters after photoassisted prereduction.

A headspace single-drop microextraction (SDME) method has been developed in combination with electrothermal atomic absorption spectrometry for determination of total inorganic Se and Se(IV). SeH(2) is generated in a 40mL volume closed-vial and trapped onto a Pd(II)-aqueous containing drop that is supported at the needle tip of a high-precision chromatographic syringe. Sample pre-treatment by UV irradiation prior to hydride generation allowed converting Se(VI) into Se(IV), hence, facilitating total Se determination. A 2(IV)(6-2) fractional factorial design was employed for characterising the effect of relevant variables over SeH(2) trapping. The variables showing the most significant effect were Pd(II) concentration in the drop and extraction time. A preconcentration factor of about 25 is achieved. The limit of detection of Se was 0.15ng/mL using trapping onto a 3-muL drop and the precision expressed as relative standard deviation was about 3%. The limit of detection could be improved further using repeated sampling of the headspace.

Application of microwave extraction for partitioning of heavy metals in sewage sludge

The four-stage Tessier sequential extraction method was used for metal fractionation in a sewage sludge sample collected from an urban wastewater processing plant. The original Tessiers method was modified, in each stage, using microwave heating in order to reduce the long operation time. Extraction conditions (heating time and power) were specifically optimised for Cu, Cr, Ni, Pb and Zn with the aim of finding extraction efficiencies similar to that of the original Tessiers method. Analytical results obtained by both the conventional and the microwave Tessier extraction methods were statistically compared (p=0.05) for all the studied elements and no significant differences (recoveries between 98.3% and 100.8%) were found for Ni, Pb and Zn in the three first stages (i.e. exchangeable, carbonate-bound and Fe–Mn oxides-bound). However, in the fourth stage (i.e. organic matter-bound), a different behaviour was found when using microwave heating since Ni and Zn were extracted with same efficiency as compared with the conventional Tessier method (recoveries of 98.8% and 100.2% for Ni and Zn, respectively), Pb was excessively leached and Cr was not leached. For Cu, although different metal partitioning pattern were obtained by applying both extraction methods, the total extractable content obtained by the microwave extraction method was only about 7% lower than that obtained by the conventional Tessier extraction method. The precision of the proposed microwave extraction method (expressed as RSD) was lower than 5% for all metals.

In Situ Building of a Nanoprobe Based on Fluorescent Carbon Dots for Methylmercury Detection

A new fluorescent assay based on in situ ultrasound-assisted synthesis of carbon dots (CDs) as optical nanoprobes for the detection of methylmercury has been developed. Application of high-intensity sonication allows simultaneous performance of the synthesis of fluorescent CDs within the analytical time scale and the selective recognition of the target analyte. Microvolume fluorospectrometry is applied for measurement of the fluorescence quenching caused by methylmercury. The assay uses low amounts of organic precursors (fructose, poly(ethylene glycol), and ethanol) and can be accomplished within 1 min. A detection limit of 5.9 nM methylmercury and a repeatability expressed as a relative standard deviation of 2.2% (N = 7) were obtained. CDs displayed a narrow size distribution with an average size of 2.5 nm as determined by electron transmission microscopy. To study the quenching mechanism, fluorescence, atomic absorption spectrometry, and Fourier transform infrared spectrometry were applied. Hydrophobicity of methylmercury and its ability to facilitate a nonradiative electron/hole recombination are suggested as the basis of the recognition event. A simple and green assay is achieved for quick detection of methylmercury without the use of tedious sample preparation procedures or complex and expensive instrumentation.

On-line high-performance liquid-chromatographic separation and cold vapor atomic absorption spectrometric determination of methylmercury and inorganic mercury

A reversed-phase high-performance liquid chromatography (HPLC) method with cold vapor atomic absorption spectrometry (CV-AAS) detection is developed for mercury speciation. In this paper, the efficiency of tetrabutylammonium bromide reagent and sodium chloride in a methanol-water mixture as mobile phase is evaluated for HPLC separation of methylmercury and inorganic mercury coupled with on-line CV-AAS determination. Both mercury species are separated on a reversed-phase C(18) column. Several parameters (e.g. composition and flow-rate of mobile phase) are investigated for the optimization of HPLC separations. CV-AAS technique parameters are also studied for their effect on sensitivity (sodium borohydride and sodium hydroxide concentrations in the reducing agent, reducing agent flow-rate, length of the reduction coil and nitrogen flow-rate). Quantitative recoveries for both inorganic mercury and methylmercury are obtained from a spiked natural water sample.