Pablo H. Pacheco

Solid phase extraction of co ions using L-tyrosine immobilized on multiwall carbon nanotubes.

A study was performed to assess the performance of aminoacids immobilized on carbon nanotubes (CNTs) for their employment as a sorbent for solid phase extraction systems. An immobilization method is introduced and the aminoacid L-tyrosine was chosen as a case study. A spectrophotometric study revealed the amount of aminoacid immobilizated on CNTs surface, and it turned to be of 3174 micromol of L-tyrg(-1). The material was tested for Co retention using a minicolumn inserted in a flow system. At pH 7.0, the amount of Co retained by the column was of 37.58+/-3.06 micromol Co g(-1) of CNTs. A 10% (v/v) HNO(3) solution was chosen as eluent. The pH study revealed that Co binding increased at elevated pH values. The calculation of the mol ratio (moles of Co bound at pH 9 to moles of l-tyr) turned to be 3:1. The retention capacity was compared to other bivalent cations and showed the following tendency: Cu(2+)>Ni(2+)>Zn(2+)>>Co(2+). The analytical performance was evaluated and an enrichment factor of 180 was obtained when 10 mL of 11.37 microg L(-1)Co solution was loaded onto the column at pH 9.0; reaching a limit of detection (LoD) of 50 ng L(-1). The proposed system was successfully applied to Co determination in QC-LL2 standard reference material (metals in natural water).

Biosorption: A new rise for elemental solid phase extraction methods

Biosorption is a term that usually describes the removal of heavy metals from an aqueous solution through their passive binding to a biomass. Bacteria, yeast, algae and fungi are microorganisms that have been immobilized and employed as sorbents in biosorption processes. The binding characteristics of microorganisms are attributed to functional groups on the surface providing some features to the biosorption process like selectivity, specificity and easy release. These characteristics turn the biosorption into an ideal process to be introduced in solid phase extraction systems for analytical approaches. This review encompasses the research carried out since 2000, focused on the employment of biosorption processes as an analytical tool to improve instrumental analysis. Since aminoacids and peptides as synthetic analogues of natural metallothioneins, proteins present in the cell wall of microorganisms, have been also immobilized on solid supports (controlled pore glass, carbon nanotubes, silica gel polyurethane foam, etc.) and introduced into solid phase extraction systems; a survey attending this issue will be developed as well in this review.

L-tyrosine immobilized on multiwalled carbon nanotubes: a new substrate for thallium separation and speciation using stabilized temperature platform furnace-electrothermal atomic absorption spectrometry.

An approach for the separation and determination of inorganic thallium species is described. A new sorbent, L-tyrosine-carbon nanotubes (L-tyr-CNTs), was used and applied to the analysis of tap water samples. At pH 5.0, L-tyr was selective only towards Tl(III), while total thallium was determined directly by stabilized temperature platform furnace-electrothermal atomic absorption spectrometry (STPF-ETAAS). The Tl(III) specie, which was retained by L-tyrosine, was quantitatively eluted from the column with 10% of nitric acid. An on-line breakthrough curve was used to determine the column capacity, which resulted to be 9.00 micromol of Tl(III) g(-1) of L-tyr-CNTs with a molar ratio of 0.14 (moles of Tl bound to moles of L-tyr at pH 5). Transient peak areas revealed that Tl stripping from the column occurred instantaneously. Effects of sample flow rate, concentration and flow rate of the eluent, and interfering ions on the recovery of the analyte were systematically investigated. The detection limit for the determination of total thallium (3sigma) by STPF-ETAAS was 150 ng L(-1). The detection limit (3sigma) for Tl(III) employing the separation system was 3 ng L(-1), with an enrichment factor of 40. The precision of the method expressed as the relative standard deviation (RSD) resulted to be 3.4%. The proposed method was applied to the speciation and determination of inorganic thallium in tap water samples. The found concentrations were in the range of 0.88-0.91 microg L(-1) of Tl(III), and 3.69-3.91 microg L(-1) of total thallium.

Total and inorganic mercury determination in biodiesel by emulsion sample introduction and FI-CV-AFS after multivariate optimization

An automated procedure for total and inorganic mercury determination in biodiesel by CV-AFS was studied. The samples were introduced directly as oil-in-water emulsions in a flow injection manifold followed by cold vapor generation coupled to atomic fluorescence spectrometry (FI-CV-AFS). After irradiation with an UV source, organic mercury (e.g.MeHg+ and PhHg+ among others) was decomposed. Mercury vapors were generated using an acidic SnCl2 solution in a continuous flow system and were then determined. This strategy reduced sample handling, avoiding sample contamination and analyte losses. The limit of detection was calculated as 0.2 µg Kg−1 (0.03 µg L−1 for the emulsions) and the relative standard deviation was better than 8% at levels of 3.0 µg L−1 in the emulsion, calculated from the peaks obtained. The accuracy was verified by comparing the results with a total microwave-assisted digestion.

On-line preconcentration and speciation analysis of inorganic vanadium in urine using l-methionine immobilised on controlled pore glass

A study was undertaken to ascertain the analytical capabilities of combined ICP-OES with ultrasonic nebulization to perform on-line preconcentration and speciation of inorganic V species in urine samples using a micro-column packed with l-methionine immobilized on controlled pore glass (CPG) as solid phase extractant. At pH 5.0, l-methionine is selective only towards V(V) while, total vanadium was quantitatively adsorbed by the solid phase at pH 9.0 [as V(V)] due to V(IV) oxidation in alkali media. Vanadium species retained by l-methionine were quantitatively eluted from the column with 10% HCl. Effects of acidity, sample flow rate, concentration of eluent and interfering ions on the recovery of the analytes have been systematically investigated. The detection limit (3sigma) of V is 0.008ngmL(-1) for USN-ICP-OES with an enhancement factor of 900 (10 for USN and 90 for l-methionine), and the relative standard deviation (R.S.D.) is better than 2%. The proposed method has been applied to the determination of inorganic V(V) and V(IV) in urine.

On-line preconcentration and speciation analysis of Se(IV) and Se(VI) using L-methionine immobilised on controlled pore glass

A study was undertaken to evaluate the analytical capabilities of the aminoacid L-methionine as a possible substrate for the selective sorption of selenium inorganic species for the determination of Se(IV) and Se(VI) in aqueous solution. Methionine was covalently immobilised on controlled pore glass (CPG), packed in a minicolumn and incorporated in an on-line flow injection system. Se was determined by flow injection hydride generation-inductively coupled plasma optical emission spectrometry (FI-HG-ICP OES). Chemical and physical variables affecting the sorption process were tested in order to select the optimal analytical conditions for the Se retention by methionine. Se(VI) was selectively retained by methionine at pH 3.0, while Se(IV) was not retained. Se(VI) was subsequently removed from the conical minicolumn with 10% HCl and on-line reduced with 12 mol l−1 HCl in a water bath (100 °C). A preconcentration factor of 90 was achieved when 30 mL of sample were processed reaching a detection limit of 11 ng l−1, with a sample throughput of 17 samples h−1 for total selenium determination and 8 samples h−1 for speciation [Se(IV) and Se(VI)]. The speciation analysis of inorganic Se in drinking water was performed following the proposed method and the recoveries were in all cases between 98 and 100%.

Optimization of methods to assess levels of As, Bi, Sb and Se in airborne particulate matter by FI-HG-ICP OES

A study was undertaken to assess the level of selected trace elements namely, As, Bi, Sb and Se in airborne particulate matter collected on ash-free glass-fibre filters from urban and industrial areas of Argentina. For sample digestion, a simple acid treatment with HCl + HF is proposed with the aim to minimize contamination and reduce sample treatment steps. A flow injection-hydride generation system in combination with inductively coupled plasma optical emission spectrometry was used. While, Se and Bi could be determined directly from the digest, As and Sb needed a pre-reduction with KI, and H3BO3 to avoid the interference of F− ions that may cause losses via volatile compounds such as AsF3 and Sb(V) complexes. Limits of detection (3σ) of 0.3 ng m−3 for As; 0.09 ng m−3 for Bi, and 0.1 ng m−3 for Sb and Se were achieved. Precision resulted in better than 6.1% accuracy for all the elements determined. Accuracy test was assessed by means of the certified reference material, NIST 1648 (urban particulate matter).

Ultratrace arsenic determination through hydride trapping on oxidized multiwall carbon nanotubes coupled to electrothermal atomic absorption spectrometry

Arsenic determination in natural waters is an issue of current research. This article reports a novel hydride generation (HG) approach developed for As determination with electrothermal atomic absorption spectrometry (ETAAS) detection. The HG process was interfaced with ETAAS through hydride trapping onto a carbon nanotubes microcolumn. To this end a homemade gas–liquid separator was used, allowing arsine formation and its flow throughout the CNT microcolumn. The retention process involved thus a solid phase extraction from the gas phase to the solid support. Once arsine generation was completed, the elution was carried out with nitric acid directly onto the dosing hole of the graphite furnace. Outstanding sensitivity with detection limit of 1 ng L−1, quantification limit of 5 ng L−1 and the characteristic mass, 5.8 ± 0.4 pg could be achieved. A satisfactory correlation between concentration of As and absorbance (R = 0.9993) from the limit of quantification up to 500 ng L−1, with a relative standard deviation of 6.3% were obtained. A sensitive enhancement factor of 38 was reached when 2 mL of sample were processed and 50 μL of HNO3 were used as eluent. The system was successfully applied to the analysis of a standard reference material, QC LL2 metals in natural waters. In addition tap water analysis provided an As concentration of 0.29 ± 0.03 μg L−1.

Vapor generation - atomic spectrometric techniques. Expanding frontiers through specific-species preconcentration. A review.

We review recent progress in preconcentration strategies associated to vapor generation techniques coupled to atomic spectrometric (VGT-AS) for specific chemical species detection. This discussion focuses on the central role of different preconcentration approaches, both before and after VG process. The former was based on the classical solid phase and liquid-liquid extraction procedures which, aided by automation and miniaturization strategies, have strengthened the role of VGT-AS in several research fields including environmental, clinical, and others. We then examine some of the new vapor trapping strategies (atom-trapping, hydride trapping, cryotrapping) that entail improvements in selectivity through interference elimination, but also they allow reaching ultra-low detection limits for a large number of chemical species generated in conventional VG systems, including complete separation of several species of the same element. This review covers more than 100 bibliographic references from 2009 up to date, found in SCOPUS database and in individual searches in specific journals. We finally conclude by giving some outlook on future directions of this field.

Selective determination of inorganic selenium species in parenteral solutions using L-methionine as retaining agent in ETAAS

A time-based flow injection (FI) separation system coupled to electrothermal atomic absorption spectroscopy (ETAAS) has been developed for the determination of selenium in parenteral solutions. Selenate interacts with L-methionine, which is immobilized on controlled pore glass (CPG), at pH 3.0 and eluted with HCl (10% v/v). Total selenium content is determined directly by ETAAS without preconcentration and selenite is calculated by difference. The features of the separation system are: 100% efficiency of retention and an enhancement factor of 20 for a pre-concentration time of 6 s (sample flow rate = 10 mL min−1) with HCl elution volumes of 50 µL. The detection limit (3σ) was 6 ng L−1, and the relative standard deviation (n = 10) at the 0.1 µg L−1 level is 3.0%. The method has high selectivity and was applied to the determination of Se (IV) and (VI) in parenteral solutions with satisfactory results.