Revisitation of mineralization modes for arsenic and selenium determinations in environmental samples

Mineralization procedures for arsenic and selenium analysis are usually limited to wet digestion methods owing to high volatility of these analytes. On the other hand, variable amounts of silicon in some types of samples imply elaborated mineralization procedures to liberate analytes which may be retained in an insoluble residue. Consequently, methods for such material generally include an hydrofluoric step followed by an evaporation to dryness. This type of mineralization is most easily accomplished using a dry ashing procedure. For plant analysis, a well validated and readily applicable dry ashing method is used for a long time in several laboratories but up today one could suppose that As and Se determinations cannot be performed after such a type of mineralization. Surprisingly, it has been observed that for plant samples these analytes are detected even after a calcination at 450 degrees C. The general usefulness of a dry ashing method for analysis of all other analytes (main, minor and trace elements) incitates us to also verify As and Se recoveries. Results obtained in this work indicate clearly that plants of terrestrial origin may be mineralized using dry ashing procedure without As and Se losses. This statement was confirmed by analyses of several reference terrestrial plant samples (RMs) and laboratory control samples. Another confirmation was given by the direct graphite furnace analysis of the same plant samples but in slurried form (SS-ETAAS). As a direct consequence, As and Se analysis in terrestrial plants no more necessitates a separate preparation methodology. On the other hand, significant losses of As and Se were observed for aquatic plants, e.g. algaes. For the analysis of this type of samples, a separate wet digestion procedure remains unavoidable if the determination of As and Se has to be considered. Also some preparation procedures were tested for As and Se-analysis of soil and sediment reference samples. In these cases the wet digestion with a mixture of nitric, perchloric and hydrofluoric acids seems to remain the best alternative.     

Determination of trace elements in AR grade alkali salts after preconcentration by column solid-phase extraction on TiO2 (anatase)

 Column solid-phase extraction using TiO₂ (anatase) as a solid sorbent was applied to preconcentrate traces of Cd, Co, Cu, Fe, Mn, Ni and Pb from AR grade alkali salts prior to their measurements by atomic absorption spectrometry (AAS). Multi-element preconcentration was achieved from NaCl, KCl, KNO₃, NaNO₃, CH₃COONa, NaHCO₃ and Na₂CO₃ solutions, whereas the sorption of trace elements from phosphates and sulfates is not quantitative. Optimal conditions (recoveries of the analytes >95%) for solid-phase co-extraction of the most common heavy metal ions are proposed. The conditions for quantitative and reproducible elution and subsequent AAS are established. A method of determination of trace elements in different salts is proposed. It is characterized by precision, reproducibility and a high preconcentration factor. The solid-phase extraction by TiO₂, combined with ETAAS allows the determination of 0.1 ng g^-1 Cd, 2 ng g^-1 Co, 1 ng g^-1 Cu and Ni, 0.5 ng g^-1 Mn and 0.4 ng g^-1 Pb. Received: 1 April 1996/Revised: 24 June 1996/Accepted: 9 July 1996     

Application of high-surface-area ZrO2 in preconcentration and determination of 18 elements by on-line flow injection with inductively coupled plasma atomic emission spectrometry

A flow-injection analysis (FIA) system incorporating a micro-column of ZrO2 has been used for the development of an on-line multi-element method for the simultaneous preconcentration and determination of Al, Bi, Cd, Co, Cr, Cu, Fe, Ga, In, Mn, Mo, Ni, Pb, Tl, V, Sb, Sn, and Zn by inductively coupled plasma atomic emission spectrometry (ICP-AES). The conditions for quantitative and reproducible preconcentration, elution, and subsequent on-line ICP-AES determination were established. A sample (pH 8) is pumped through the column at 3 mL min(-1) and sequentially eluted directly into the ICP-AES with 3 mol L(-1) HNO3. With a sample volume of 100 mL and an elution volume of 1 mL signal enhancement 100 times better than for conventional continuous aspirating systems was obtained for the elements studied. The reproducibility (RSD %) of the method at the 10 ng mL(-1) level in the eluate is acceptable - less than 8% for five replicates. Recoveries between 95.4% and 99.9% were obtained for the elements analysed. ZrO2, with a specific surface area of 57 m2 g(-1) and a capacity of approximately 5 mg g(-1) for the elements studied, was synthesized by hydrolysis of ZrCl4. The preconcentration system was evaluated for several simple synthetic matrices, standard water samples and synthetic seawater. The effect of foreign ions on the efficiency of preconcentration of the elements studied was investigated. The application of a micro-column filled with high-surface-area ZrO2 and flow injection inductively coupled plasma atomic emission spectrometry enables preconcentration and simultaneous determination of 18 elements at low concentrations (ng L(-1)) in different water samples.     

Practical Syntheses of Functionalized 1-Oxo-L,2,3,4-Tetrahydro-β-carboline-3-carboxylic Acid Esters

Three methods have been proposed for the preparation of functionalized 1-oxo-1,2,3,4-tetrahydro-β-carboline-3 carboxylates (3) from which the “acylazide formation-Curtius rearrangement-acid catalyzed ring closure” sequence starling from hemi-ester hemi-acids (8) seemed to be quite general.     

Phosphorus as sintering activator in powder metallurgical steels: characterization of the distribution and its technological impact

Powder metallurgy is a highly developed method of manufacturing reliable ferrous parts. The main processing steps in a powder metallurgical line are pressing and sintering. Sintering can be strongly enhanced by the formation of a liquid phase during the sintering process when using phosphorus as sintering activator. In this work the distribution (effect) of phosphorus was investigated by means of secondary ion mass spectrometry (SIMS) supported by Auger electron spectroscopy (AES) and electron probe micro analysis (EPMA). To verify the influence of the process conditions (phosphorus content, sintering atmosphere, time) on the mechanical properties, additional measurements of the microstructure (pore shape) and of impact energy were performed. Analysis of fracture surfaces was performed by means of scanning electron microscopy (SEM). The concentration of phosphorus differs in the samples from 0 to 1% (w/w). Samples with higher phosphorus concentrations (1% (w/w) and above) are also measurable by EPMA, whereas the distributions of P at technically relevant concentrations and the distribution of possible impurities are only detectable (visible) by means of SIMS. The influence of the sintering time on the phosphorus distribution will be demonstrated. In addition the grain boundary segregation of P was measured by AES at the surface of in-situ broken samples. It will be shown that the distribution of phosphorus depends also on the concentration of carbon in the samples.     

Determination of methylmercury in marine sediment samples: Method validation and occurrence data

The determination of methylmercury (MeHg) in sediment samples is a difficult task due to the extremely low MeHg/THg (total mercury) ratio and species interconversion. Here, we present the method validation of a cost-effective fit-for-purpose analytical procedure for the measurement of MeHg in sediments, which is based on aqueous phase ethylation, followed by purge and trap and hyphenated gas chromatography–pyrolysis–atomic fluorescence spectrometry (GC–Py–AFS) separation and detection. Four different extraction techniques, namely acid and alkaline leaching followed by solvent extraction and evaporation, microwave-assisted extraction with 2-mercaptoethanol, and acid leaching, solvent extraction and back extraction into sodium thiosulfate, were examined regarding their potential to selectively extract MeHg from estuarine sediment IAEA-405 certified reference material (CRM). The procedure based on acid leaching with HNO₃/CuSO₄, solvent extraction and back extraction into Na₂S₂O₃ yielded the highest extraction recovery, i.e., 94 ± 3% and offered the possibility to perform the extraction of a large number of samples in a short time, by eliminating the evaporation step. The artifact formation of MeHg was evaluated by high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC–ICP–MS), using isotopically enriched Me²⁰¹Hg and ²⁰²Hg and it was found to be nonexistent. A full validation approach in line with ISO 17025 and Eurachem guidelines was followed. With this in mind, blanks, selectivity, working range (1–800 pg), linearity (0.9995), recovery (94–96%), repeatability (3%), intermediate precision (4%), limit of detection (0.45 pg) and limit of quantification (0.85 pg) were systematically assessed with CRM IAEA-405. The uncertainty budget was calculated and the major contribution to the combined uncertainty (16.24%, k = 2) was found to arise from the uncertainty associated with recovery (74.1%). Demonstration of traceability of measurement results is also presented. The validated measurement procedure was applied to the determination of MeHg incurred in sediments from a highly polluted and scarcely studied area in the Caribbean region.     

Elucidation of the chemical and morphological structure of double-network (DN) hydrogels by high-resolution magic angle spinning (HRMAS) NMR spectroscopy

(1)H HRMAS NMR spectroscopy is applied to gain insight into the chemical and morphological structure of double-network (DN) hydrogels, prepared from poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) and poly(acrylamide) (PAAm). The method enables one to obtain detailed information at the molecular level about the formation of covalent bonds between the two polymer networks through non-reacted double bonds of the cross-linker N,N'-methylene bis(acrylamide) (MBAA). Evidence to the existence of strong hydrogen-bond interactions based on the N-H group of the PAMPS as a hydrogen-bond donor and the C=O group of the PAAm as a hydrogen-bond acceptor is also provided. These findings clarify the origin of the toughening mechanism and the exceptionally strong mechanical properties of DN gels, further supported by microhardness data.     

TrainMiC®: a programme for life-long learning in metrology in chemistry

This article gives an overview of the programme TrainMiC^®, a European programme for Life-Long Learning in metrology in chemistry. It explains its raison d’être and puts it into perspective to other European and EU member states initiatives. The TrainMiC^® system (http://www.trainmic.org) is described in detail. It is explained how it has developed into a truly unique system which is operational across many parts of Europe (19 countries) via national teams. These teams use shareware pedagogic tools. The learning content has been harmonised at the European level by a joint effort of many experts across Europe working via an Editorial Board. The material has been translated in ten different languages. Possible future evolution of this Life Long Learning programme is discussed.     

First results on Fe solid-phase extraction from coastal seawater using anatase TiO2 nano-particles

This paper describes the application of TiO₂ nano-particles (anatase form) for the solid-phase extraction of iron from coastal seawater samples. We investigated the adsorption processes by infra-red spectroscopy. We compared in batch and on-(mini)column extraction approaches (0.1 and 0.05 g TiO₂ per sample, respectively), combined to external calibration and detection by inductively coupled plasma mass spectrometry at medium mass resolution. Globally, this titania phase was slightly more efficient with seawater than with ultra-pure water, although between pH 2 and pH 7, the Fe retention efficiency progressed more in ultra-pure water than in seawater (6.9 versus 4.8 times improvement). Different reaction schemes are proposed between Fe(III) species and the two main categories of titania sites at pH 2 (adsorption of [FeL _x ]^{(3 − x)+} via possibly the mediation of chlorides) and at pH 7 (adsorption of [Fe(OH)₂]⁺ and precipitation of [Fe(OH)₃]⁰). Under optimised conditions, the inlet system was pre-cleaned by pumping 6% HCl for ∼2 h, and the column was conditioned by aspirating ultra-pure water (1.7 g min⁻¹) and 0.05% ammonia (0.6 g min⁻¹) for 1 min. Then 3 g seawater sample was loaded at the same flow rate while being mixed on-line with 0.05% ammonia at 0.6 g min⁻¹ to adjust the pH to 7. The iron retained on the oxide powder was then eluted with 3 g 6% HCl (<0.002% residual salinity in the separated samples). The overall procedural blank was 220 ± 46 (2 s, n = 16) ng Fe kg⁻¹ (the titania was renewed in the column every 20 samples, with 2-min rinsing in between samples with 6% HCl at 1.5 g min⁻¹). The recovery estimated from the Canadian certified reference material CASS-2 was 69.5 ± 7.6% (2 s, n = 4). Typically, the relative combined uncertainty (k = 2) estimated for the measurement of ∼1 μg Fe kg⁻¹ (0.45 μm filtered and acidified to pH 1.5) of seawater was ∼12%. We applied our method to a similar sample, from the coastal region of the North Sea. The agreement well within stated uncertainties of our result with the value obtained independently by isotope dilution mass spectrometry further validated our method.