Isabel Padilla

Preconcentration and matrix separation of precious metals in geological and related materials using metalfix-chelamine resin prior to inductively coupled plasma mass spectrometry

Abstract A method for determining Au, Pt, Pd, Ir and Rh in ores and silicates and Fe-formation rocks is described. Sample decomposition was carried out with aqua regia and HF, followed by fusion of any insoluble residue with Na22O2 in a glassycarbon crucible. The precious metals were separated, in 1.2 mol dm−3 HCl media, from the matrix elements by ion-exchange, using a mini-column with tetraethylenepentamine (metalfix-chelamine) resin. The resin was destroyed with HNO3 and H2O2 in a high-pressure vessel assisted by microwave heating, and the precious elements were determined by flow-injection inductively coupled plasma mass spectrometry. The sample treatment, optimization of analytical variables and measurable concentration levels are discussed. The limits of quantification (10 sdn − 1) calculated from a procedural blank sample solution were 4.0, 2.0, 1.5, 0.8 and 0.5 ng g−1 for Au, Pt, Pd, Ir and Rh, respectively. The accuracy of the proposed method was tested by determining these elements in SARM 7 platinum-ore reference material. For all the analytes, the relative standard deviation of the combined dissolution, separation and determination methods was below 3.5% (n = 6).

Aminoglycoside antibiotics: structure, functions and effects on in vitro plant culture and genetic transformation protocols.

Plant transformation protocols generally involve the use of selectable marker genes for the screening of transgenic material. The bacterial gene nptII, coding for a neomycin phosphotransferase, and the hpt gene, coding for a hygromycin phosphotransferase, are frequently used. These enzymes detoxify aminoglycoside antibiotics by phosphorylation, thereby permitting cell growth in the presence of antibiotics. Nevertheless, the screening for transgenic regenerated shoots is often partial and difficult due to regeneration of escapes and chimeras. These difficulties can be caused, in part, by an incorrect assumption about the mode of action of antibiotics in bacterial and eukaryotic cells and in in vitro tissue culture. The information contained in this review could be useful to establish better selection strategies by taking into account factors such as explant complexity, transformation and selection protocols that allow better accessibility to cells of Agrobacterium and antibiotics, and faster regeneration methods that avoid collateral effects of antibiotics on recovered, putative transgenic shoots.

Concerns on liquid mercury and mercury-containing wastes: a review of the treatment technologies for the safe storage.

Due to the adverse effects of mercury on human health and the environment, restrictive legislations and world-wide common efforts are now under way to reduce both the supply and demand of mercury. As a result, all excess Hg must be stored in safe conditions in secure places. This paper is an attempt to review the various treatment technologies types of liquid mercury (Hg(0)) and mercury-containing wastes, which can be used to store these residues in a safe way. The different treatments were classified as a function of the waste treated. The main treatments described are amalgamation, formation of sulfides, thermal treatments, vitrification, soil washing, sulfur polymer stabilization solidification, chemically bonded phosphate ceramics and other encapsulation processes, being highlighted the stabilization/solidification processes that are the treatments that provide better results, according to the consulted bibliography.

Phosphine oxide mediate transport: modelling of mass transfer in supported liquid membrane transport of gold (III) using Cyanex 923

The permeation of gold (III) through a supported liquid membrane impregnated with the phosphine oxide Cyanex 923 in n-decane has been investigated. A model is reported describing the transport mechanism which consists of: di6usion process through the feed aqueous di6usion layer, fast interfacial chemical reaction and di6usion through the membrane. The experimental data are quantitatively explained by mathematical equations describing the rate of transport. Di6erent rate-controlling processes take place as long as the metal transport occurs. High selectivity in the separation of gold (III) with respect to the platinum group metals is achieved. ? 2001 Elsevier Science Ltd. All rights reserved.

Slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry for steelmaking flue dust analysis

Abstract A commercial atomic absorption graphite furnace (AAGF), with a self-made adapter and valve system, was used as a slurry sampling cell for electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS). The system was applied to the determination of As, Sn, Sb, Se, Te, Bi, Cd, V, Ti and Mo in steelmaking flue dusts. Experimental conditions with respect to ETV and ICP-MS operating parameters were optimized. Compared to aqueous solutions, slurry samples were found to present better analyte transport. Microgram amounts of Rh were used to reduce the difference in analyte response in sensitivity for aqueous solutions of the tested analytes. No such increasing effect was observed for slurry samples and aqueous standards. An added quantity of Rh acting as modifier/carrier resulted in an increase for the same analytes in matrix-slurry solutions, even the addition of an extra Rh quantity has resulted in a decrease in the signals. The effect of Triton X-100 (used as a dispersant agent) on analyte intensity and precision was also studied. External calibration from aqueous standards spiked with 100 μg ml −1 Rh was performed to quantified 0.010 g/100 ml slurry samples. Results are presented for a certified reference electrical arc furnace flue dust (EAF): CRM-876-1 (Bureau of Analysis Samples Ltd., Cleveland, UK), a reference sample of coke ashes X-3705 (from AG der Dillinger Huttenwerke, Germany), and a representative sample of EAF flue dust from a Spanish steelmaking company (CENIM-1). For the two reference materials an acceptable agreement with certificate values was achieved, and the results for the CENIM sample matched with those obtained from conventional nebulization solution.

Use of boric acid to improve the microwave-assisted dissolution process to determine fluoride forming elements in steels by flow injection inductively coupled plasma mass spectrometry

The applicability of FI-ICP-MS combined with microwave sample digestion for the simultaneous determination of trace amounts of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu in iron and steel samples was investigated. The use of hydrofluoric acid in the sample dissolution process produced nearly invisible insoluble particles with the REEs, leading to erroneous quantification of these elements. The addition of boric acid, complexing HF, solved this problem. By monitoring the transient signals produced by the FI microsampling system, it was possible to evaluate the effectiveness of the sample dissolution procedure. Severe depressive matrix effects caused by the sample matrix were encountered when the signals were compared with those from HNO3 solutions; in contrast, no effects were observed with the addition of boric acid. A highly alloyed steel, stainless steel certified reference material JK 37 (Sandvik Steel), was used to evaluate the effectiveness of the dissolution procedure and to develop the method. The limits of quantification (LOQ) calculated on the basis of 10√s ranged between 0.008 µg g–1 for Lu and 0.040 µg g–1 for Nd. The relative standard deviation for all the analytes was better than 3% (n=4) for concentrations above 10 times the LOQ.

Dispersion-free solvent extraction of Cr(VI) from acidic solutions using hollow fiber contactor.

The use of dispersión-free solvent extraction, through microporous hydrophobic membrane has been investigated. The hollow fiber contactor, with surface area of 1.4 m2 was used to extract Cr(VI) (0.005-0.12 g/L from aqueous sulphuric acidic media (pH 2.5-4.2 +/- 0.05). Several parameters such as extractant concentration, feed acidity and metal concentration in the initial aqueous solution were investigated. Results revealed that 15% v/v Cyanex 923 in Exxsol D-100 as organic phase and feed in the 2.5 pH range, gave optimum extraction (exceeding 95%) of Cr(VI) and it was possible to strip using 10 g/L hydrazine sulfate (also with recoveries exceeding 95%). In this step, Cr(VI) is immediately reduced to the less hazardous Cr(III) state. Results also showed that under the various experimental conditions, chromium(VI) extraction was rate-controlled by the interfacial reaction on the membrane surface. Typical overall mass transfer coefficients values are 4.2 x 10(-5) and 3.6 x 10(-6) cm/s for extraction and stripping operations, respectively.

Study of heterogeneities in steels and determination of soluble and total aluminium and titanium concentration by laser ablation inductively coupled plasma mass spectrometry

A methodology for bulk analysis of Al and Ti and for determination of soluble and total Al and Ti concentration in steel samples by laser ablation inductively coupled plasma mass spectrometry was developed. The spatial distribution (both at surface and within the sample) of the insoluble fraction of Al and Ti was also qualitatively estimated. Certified reference materials (CRMs) SS-451 to 460 (carbon steel) and 064-1 (Nb/Ti interstitial free steel), from BAS, and JK 2D (carbon steel) and JK 37 (highly alloyed steel), from SIMR, were studied. It was demonstrated that the insoluble fraction of Al and Ti is heterogeneously distributed. A series of nine glass samples (fused beads) with fixed Fe content and different Al and Ti contents was prepared by melting appropriate amounts of Fe(2)O(3), Al(2)O(3) and TiO(2) with a lithium tetraborate-sodium carbonate mixture. Quantitative determinations were performed by using calibration graphs obtained from the synthetic fused beads, with (57)Fe as internal standard; line scan laser sampling mode was used, focusing the laser beam at the sample surface. The optimized laser operating parameters were: laser pulse energy of 1.5mJ, pulse repetition rate of 5Hz, scanning speed of 5microm s(-1) and preablation time of 20s. The concentrations obtained for bulk analysis of CRM samples corresponded with the certified values within the experimental uncertainty. An acceptable concordance between certified and found values was attained for the determination of soluble and total Al and Ti in CRM 064-1 sample.

Spark ablation inductively coupled plasma mass spectrometry analysis of minor and trace elements in low and high alloy steels using single calibration curves

A unidirectional high current pulse spark with a very fast rise-time, ensuring a rapid and complete transfer of energy to the sample, was used as the sampling system for the analysis of carbon steels and highly alloyed steels with the same operating conditions. The sparking operating conditions were optimised and a restrictive path was designed to decrease the quantity of eroded material reaching the plasma, in order to prevent deposition of material in the torch injector, and to minimise sampling cone blockage and drift effects. Spark ablation sampling efficiency and effectiveness of the restrictive path were evaluated. To compensate for differences in the amount of material ablated or for a variation in drift, 57 Fe and 55 Mn were used as internal standards. The calibration procedure was applied to the analysis of the elements Al, B, Co, Cu, Mn, Nb, P, Si, and V, present in the following certified reference materials: BCS (Bureau of Analysed Samples) SS-456 to SS-460 (residual series); CRMs (European Committee for Iron and Steel Standardisation) No 285-2 (Maraging steel), No 292-1 (niobium stabilised steel), No 295-1 (highly alloyed steel), and No 296-1 (jethete steel). When plotting intensity ratios (I X /I IS ) versus concentration ratios (C X /C IS ) linear calibration curves over the entire range of tested concentrations, with correlation coefficients better than 0.999, were obtained. Determination limits below 1 µg g –1 were found and the precision was better than 2.8%. It has also been shown to determine carbon contents at concentration levels greater than 0.03% with RSD values below 3%. For the elements As, Sn, Ti, W and Zr, only present in one or two of the Standard Materials, the sensitivity was also evaluated. Furthermore, the possibility of obtaining reproducible transient signals from sparking periods of only a few seconds was demonstrated.

Determination of minor elements in steelmaking flue dusts using laser ablation inductively coupled plasma mass spectrometry.

Element determination in solid waste products from the steel industry usually involves the time-consuming step of preparing a solution of the solid. Laser ablation (LA) inductively coupled plasma mass spectrometry (ICP-MS) has been applied to the analysis of Cr, Ni, Cu, As, Cd and Sn, elements of importance from the point of view of their impact on the environment, in electric arc furnace flue dust (EAFD). A simple method of sample preparation as pressed pellets using a mixture of cellulose and paraffin as binder material was applied. Calibration standards were prepared spiking multielement solution standards to a 1:1 ZnO+Fe(2)O(3) synthetic matrix. The wet powder was dried and mechanically homogenised. Quantitative analysis were based on external calibration using a set of matrix matched calibration standards with Rh as a internal standard. Results obtained using only one-point for calibration without matrix matched, needing less time for standardization and data processing, are also presented. Data are calculated for flue dust reference materials: CRM 876-1 (EAFD), AG-6203 (EAFD), AG-6201 (cupola dust) and AG-SX3705 (coke ashes), and for two representative electrical arc furnace flue dusts samples from Spanish steelmaking companies: MS-1 and MS-2. For the reference materials, an acceptable agreement with certificate values was achieved, and the results for the MS samples matched with those obtained from conventional nebulization solutions (CN). The analytical precision was found to be better than 7% R.S.D. both within a single pellet and between several pellets of the same sample for all the elements.