Trends in sorption preconcentration combined with noble metal determination.

Nowadays much attention is being paid to the determination of trace amounts of noble metals in geological, industrial, biological and environmental samples. The most promising techniques, such as inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS) and electrothermal atomic absorption spectrometry (ETAAS) are characterized by high sensitivity. However, the accurate determination of trace noble metals has been limited by numerous interferences generated from the presence of matrix elements. To decrease, or eliminate, these interferences, the sorption preconcentration of noble metals is often used prior to their instrumental detection. A great number of hyphenated methods of noble metal determination using sorption preconcentration have been developed. This review describes the basic types of available sorbents, preconcentration procedures and preparations of the sorbent to the subsequent determination of noble metals. The specific features of instrumental techniques and examples of ETAAS, FAAS, ICP-AES, ICP-MS determinations after the sorption preconcentration of noble metals are considered. The references cited here were selected mostly from the period 1996 - 2006.     

Flow Sorption–Spectroscopic Analysis

Combinations of the dynamic sorption preconcentration of elements with spectroscopic determination techniques was considered. The use of sorption systems in flow spectroscopic techniques are discussed, and the evaluation of the efficiency of these systems in the preconcentration of elements is described. The application of flow sorption–spectroscopic techniques to the determination of elements in natural water, drinking water, soil, food stuffs, rocks, and ores is surveyed.     

Sorption preconcentration in combined methods for the determination of noble metals

Combined methods for the determination of noble metals with the use of sorption preconcentration with complexing, anion-exchange, and other sorbents are reviewed. Characteristics of sorbents, techniques of sorption preconcentration, and techniques for the preparation of a concentrate for determination are considered. Features of instrumental methods for the determination of noble metals in the analysis of different materials are discussed. Examples of the use of sorption preconcentration in combined methods for the determination of noble metals are given from publications between 1996–2005.     

Filters for the Preconcentration of Elements from Solutions

The main techniques for the preconcentration of elements on thin-layer filters are considered: sorption on filters with noncovalently immobilized reagents, bonded groups, and mechanically fixed sorbents and the extraction of elements on filters as poorly soluble and polymeric forms previously formed in solution. The matrix of the filters is cellulose, synthetic polymers of the linear and branched structures, synthetic fibers, reversed-phase silica gels, foamed polyurethanes, etc. The variation of the nature of the bonded group or the reagent introduced into the solution, the matrix material, and the technique for the immobilization of groups provides the preconcentration of elements with regard to the peculiarities of test materials and the method for the subsequent determination of elements. Methods for the determination of elements in different samples including preconcentration on filters are considered.     

Possibilities for the simultaneous preconcentration and flame atomic absorption spectrometric determination of Cr(III) and Cr(VI) using a C18 column and sorption loop

The sorption loop as a preconcentration unit used so far in the low-pressure flow injection (FI) system was combined with the hydraulic high-pressure nebulizer (HHPN) and a high-pressure liquid chromatographic (HPLC) column. Thus, the sorption preconcentration of Cr(VI) can be coupled to a powerful sample introduction method or preconcentration techniques of Cr(III). The subsequent determination of the Cr(VI) content of the samples was carried out by flame atomic absorption (FAAS).     

Derivative flame atomic absorption spectrometry and its application in trace analysis

Flame atomic absorption spectrometry (FAAS) is an accepted and widely used method for the determination of trace elements in a great variety of samples. But its sensitivity doesn’t meet the demands of trace and ultra-trace analysis for some samples. The derivative signal processing technique, with a very high capability for enhancing sensitivity, was developed for FAAS. The signal models of conventional FAAS are described. The equations of derivative signals are established for FAAS, flow injection atomic absorption spectrometry (FI-FAAS) and atom trapping flame atomic absorption spectrometry (AT-FAAS). The principle and performance of the derivative atomic absorption spectrometry are evaluated. The derivative technique based on determination of variation rate of signal intensity with time (dI/dt) is different from the derivative spectrophotometry (DS) based on determination of variation rate of signal intensity with wavelength (dI/dλ). Derivative flame atomic absorption spectrometry (DFAAS) has higher sensitivity, lower detection limits and better accuracy. It has been applied to the direct determination of trace elements without preconcentration. If the derivative technique was combined with several preconcentration techniques, the sensitivity would be enhanced further for ultra-trace analysis with good linearity. The applications of DFAAS are reviewed for trace element analysis in biological, pharmaceutical, environmental and food samples.     

High-sensitivity X-ray fluorescence analysis of solutions with the use of a sorption accumulation microsystem

A mass-transfer kinetic model is proposed for an embedded sorption accumulation microsystem based on polycapillary structures to be used in the developed X-ray fluorescence analyzer with preconcentration. The model is used to substantiate a kinetic method for high-sensitivity X-ray fluorescence determination of elements in multicomponent solutions. With the use of this model, experimental data on X-ray fluorescence spectra are analyzed and kinetic and equilibrium parameters are found for the sorption of copper, nickel, manganese, iron, and zinc on the selective DETATA sorbent.     

Application of iminodiacetate chelating resin muromac A-1 in on-line preconcentration and inductively coupled plasma optical emission spectroscopy determination of trace elements in natural waters

On-line system incorporating a microcolumn of Muromac A-1 resin was used for the developing of method for preconcentration of trace elements followed by inductively coupled plasma (ICP) atomic emission spectrometry determination. A chelating type ion exchange resin has been characterized regarding the sorption and subsequent elution of 24 elements, aiming to their preconcentration from water samples of different origins. The effect of column conditioning, pH and flow rate during the preconcentration step, and the nature of the acid medium employed for desorption of the retained elements were investigated. A sample (pH 5) is pumped through the column at 3 ml min⁻¹ and sequentially eluted directly to the ICP with 3 M HNO₃/HCl mixtures. In order to remove residual matrix elements from the column after sample loading a short buffer wash was found to be necessary. The effectiveness of the matrix separation process was illustrated. The procedure was validated by analyzing several simple matrices, Standard River water sample as well as artificial seawater. Proposed method can be applied for simultaneous determination of In, Tl, Ti, Y, Cd, Co, Cu and Ni in seawater and for multielement trace analysis of river water. Recovery at 1 μg l⁻¹ level for the determination of investigated 24 elements in pure water ranged from 93.1 to 96% except for Pd (82.2%) and Pb (88.1%). For the same concentration level for seawater analysis recovery was between 81.9 and 95.6% except for Hg (38.2%).     

Preconcentration of Polycyclic Aromatic Hydrocarbons on Polyurethane Foams and Their Determination in Waters with the Use of Luminescence and High-Performance Liquid Chromatography

A technique was developed for the sorption preconcentration of polycyclic aromatic hydrocarbons on polyurethane foams in the batch and dynamic modes providing their simultaneous quantitative extraction. A procedure was proposed for screening waters for polycyclic aromatic hydrocarbons based on the preconcentration of these compounds with polyurethane foam, determination of their total amount by the luminescence method, desorption of adsorbed compounds with acetonitrile, and determination of individual compounds in the eluate by high-performance liquid chromatography with fluorescence detection. The procedure was tested with model and real samples of water.     

On-line coupling of sorption preconcentration to liquid-chromatographic methods of analysis

Methods of analysis combining the on-line sorption preconcentration of analytes with their subsequent separation and determination by high-performance liquid chromatography are considered. Approaches to the selection of sorbents, the sizes of preconcentration columns, and the sorption and desorption conditions are discussed along with the corresponding instrumentation. Many examples of the determination of organic compounds of different polarity and organic and inorganic ions are presented.     

A comparison of enrichment factor of knotted and serpentine reactors using flow injection sorption and preconcentration for the off-line determination of some trace elements by inductively coupled plasma mass spectrometry

The preconcentration efficiency expressed as an enrichment factor (EF) in knotted and serpentine reactors (SR) for FI sorption and preconcentration for the off-line determination of Cd(II), Ni(II), Co(II),Cu(II), Pb(II), Zn(II), Mo(VI), Cr(VI) and W(VI) with ICP-MS was investigated. The preconcentration was carried out by the formation of metal–pyrrolidine dithiocarbamate complex in an acidic solution and sorbed onto the inner wall of the PTFE reactors. The EFs were determined as the ratio between the analyte intensities after preconcentration using the reactors and that obtained without using the reactors. Comparing the two procedures for the equal reactor length (150 cm), the higher EFs obtained by using knotted reactor (KR) were observed for all elements. With the preconcentration time of 120 s and a sample flow rate of 1.2 ml min⁻¹, the EFs of 4–36 and 3–12 were gained using knotted and SRs, respectively. The results obtained indicate that the KR is preferable to use for flow injection sorption preconcentration system over the SR.     

Use of factorial design and Doehlert matrix for multivariate optimisation of an on-line preconcentration system for lead determination by flame atomic absorption spectrometry

A system for on-line preconcentration and determination of lead by flame atomic absorption spectrometry (FAAS) was proposed. It was based on the sorption of lead(II) ions on a minicolumn of polyurethane foam loaded with 2-(2-thiazolylazo)-5-dimethylaminophenol (TAM). The optimisation step was carried out using two-level full factorial and Doehlert designs for the determination of the optimum conditions for lead preconcentration. The proposed procedure allowed the determination of lead with a detection limit of 2.2 microg L(-1), and a precision, calculated as relative standard deviation (RSD), of 2.4 and 6.8 for a lead concentration of 50.0 and 10.0 microg L(-1), respectively. A preconcentration factor of 45 and a sampling frequency of 27 samples per hour were obtained. The recovery achieved for lead determination in the presence of several cations demonstrated that this procedure has enough selectivity for analysis of environmental samples. The validation was carried out by analysis of certified reference material. This procedure was applied to lead determination in natural food.     

Polyacrylic acid-modified alumina for solid-phase extraction and preconcentration of trace iron and chromium from plant samples

A new method is presented for simultaneous preconcentration of trace Fe(III) and Cr(III) by using polyacrylic acid-alumina as a sorbent. The separation/preconcentration conditions of analytes were investigated, including effect of pH, flow rate, elution conditions, sample volume, and interfering ions. At pH 4, the maximum sorption capacities of Fe3+ and Cr3+ were 8.0 and 13.0 mg/g, respectively, by the column method. The linearity was maintained in the concentration range of 0.175-6.0 x 10(3) ng/mL for iron and 0.175-8.0 x 10(3) ng/mL for chromium in the original solution. The RSD values under optimum conditions were +/- 1.73 and +/- 1.28% for 2.0 microg/mL Fe and Cr, respectively. The preconcentration factor was 400 for both of the elements, and detection limits were 0.025 and 0.023 ng/mL for Fe and Cr in the original solutions. The proposed method was successfully applied to the determination of trace amounts of Fe and Cr in plant samples.     

Sample Preparation Techniques—An Important Part in Trace Element Analysis for Environmental Research and Monitoring

Abstract

For the determination of minute amounts of elements in environmental samples combined analytical procedures are frequently employed. The combination of suitable sample preparation techniques with adequate detection methods lead to powerful analytical procedures. Decomposition methods are an important part of combined procedures for the determination of trace elements in solid samples. After a short summary of the potential sources for systematic errors two new decomposition methods are described that are suitable for the ashing of organic environmental samples. In one method the organic sample is ashed in a high-frequency excited oxygen plasma. The second method is a high pressure decomposition that permits mineralization of the sample in sealed quartz vessels with nitric acid at temperatures up to 320°C.

For both methods the ratio of sample weight to decomposition reagents is comparatively high. This makes these methods in combination with adequate detection methods suitable for the determination of elements at very low concentrations.

X-ray fluorescence spectrometry combined with adequate preconcentration methods is very well suited for the simultaneous determination of trace elements. Following a critical evaluation of various preconcentration techniques the analytical characteristics of filter paper with immobilized complexing agents are described. Particular emphasis is given to filter papers with dithiocarbamates as chelating group.     

Determination of Hg from Cu concentrates by X-ray fluorescence through preconcentration on polyurethane foam

A methodology was developed for the separation and determination of microamounts of mercury from copper concentrate samples by wavelength dispersive X-ray fluorescence (WDXRF) after solid-phase extraction of mercury from iodide medium using polyurethane foam (PUF). The best sorption conditions for the Hg-KI-PUF system were settled using X-ray fluorescence technique after collection of ground PUF on a filter paper by vacuum filtration and direct measurement of the intensity signal of the sorbed mercury on PUF. The main parameters of sorption such as iodide concentration, pH, shaking time and sample dilution effect were studied. The system shows rapid kinetic sorption and maximum X-ray intensity signal was achieved after shaking for 2 min a 0.01 mol l⁻¹ iodide solution containing microamounts of mercury in the pH range from 1.0 to 9.0. Effective sorption up to a volume of 0.9 l allows preconcentration of mercury. A linear fit up to 50 μg mercury was obtained by the plot of the initial mercury mass in the bulk solution (0.5 l) vs. its respective XRF intensity signal measurement on ground PUF after the sorption process. The calibration sensitivity, quantification and detection limits found were 9.09 CPS μg⁻¹, 9.0 and 2.7 μg, respectively. The sorption of many elements was also evaluated under the best conditions. High concentrations of Cu(II) and Fe(III) interfere seriously. Mercury-selective separation could be achieved using citrate or EDTA as masking agent; no interference due to copper matrix samples was observed in citrate medium. This methodology was evaluated by recovery for mercury determination in copper concentrate ore samples supplied by a mining industry and copper sulfate salts; the results were between 98% and 106%.     

Preconcentration of copper with dithizone-naphthalene for subsequent determination by atomic absorption spectrometry

A simple and convenient method for the separation and preconcentration of copper from aqueous samples has been developed. The procedure is based on the chemical sorption of copper(II) onto a column packed with immobilized dithizone on microcrystalline naphthalene. The trapped copper is eluted with 10 mL of 4 M nitric acid and determined by flame atomic absorption spectrometry. A preconcentration factor of 200 was obtained for a volume of 2 L. The relative standard deviation for the determination of 5 and 10 μg/L copper was 2.2 and 1.7%, respectively. The procedure was successfully applied to the determination of copper in water and alloy samples. The accuracy was assessed through the analysis of certified reference materials or recovery experiments. The text was submitted by the authors in English.     

Use of a new type of 8-hydroxyquinoline-5-sulphonic acid cellulose (sulphoxine cellulose) for the preconcentration of trace metals from highly mineralised water prior their GFAAS determination

Sulphoxine cellulose microcolumn was used in an FI-GFAAS system for the preconcentration of trace metals, Cd, Co, Ni, Pb and V from water and from highly mineralised water and also in the presence of complexing agent, e.g. citrate. The recovery was quantitative at pH 5 for all of the elements from NIST 1643c trace elements in water SRM and from highly mineralised water samples. No significant difference was found in the sorption of V(IV) and V(V) during preconcentration. The preparation of the 8-hydroxyquinoline-5-sulphonic acid cellulose (sulphoxine-cellulose) by Mannich reaction from aminoethyl cellulose or via chlorodeoxy and ethylenediamine cellulose is also described.     

Some Aspects on Preconcentration for Neutron Activation Analysis

A preconcentration method incorporated with neutron activation analysis was developed for the accurate determination of trace metals in biological and environmental samples. Bismuth diethyldithiocarbamate, thallium diethyldithiocarbarnate, and ammonium pyrrolidinedithiocarbamate were used as the preconcentration agents for three groups of metals. Trace metals were enriched and interfering elements such as Na, Br, P. K. etc. were removed simultaneously during the preconcentration process so that the sensitivity for each metal was greatly improved. Optimal conditions for sample digestion, group preconcentration of trace metals and neutron activation analysis of biological and environmental samples were discussed.     

Solid phase extraction of lead by Chelest Fiber Iry (aminopolycarboxylic acid-type cellulose)

Aminopolycarboxylic acid-type cellulose (Chelest Fiber Iry) has been studied for its sorption efficiencies with respect to lead from acidic solution. The influence pH and other properties related to sorption kinetic, isotherm, maximum capacity, stability and the mechanism of the sorption were discussed.Lead was quantitatively retained on the proposed adsorbent in the pH range of 2.5-5.5 (studied pH range 1.5-5.5). The maximum sorption capacity was found to be 0.86±0.06 mmol/g adsorbent. The decline in the efficiency of the adsorbent was not observed for repeated adsorption-desorption cycles. It was found that the preconcentration factor of 200 can be achieved. The limit of determination was found to be about 1 μg Pb/2 l. The method was applied to the determination of lead in water samples.     

Amberlite XAD-7 impregnated with Xylenol Orange: a chelating collector for preconcentration of Cd(II), Co(II), Cu(II), Ni(II), Zn(II) and Fe(III) ions prior to their determination by flame AAS

A new chelating resin, Xylenol Orange coated Amberlite XAD-7, was prepared and used for preconcentration of Cd(II), Co(II), Cu(II), Fe(III), Ni(II) and Zn(II) prior to their determination by flame atomic absorption spectrophotometry. The optimum pH values for quantitative sorption of Cd(II), Co(II), Cu(II), Fe(III), Ni(II) and Zn(II) are 4.5-5.0, 4.5, 4.0-5.0, 4.0, 5.0 and 5.0-7.0, respectively, and their desorptions by 2 mol L(-1) HCl are instantaneous. The sorption capacity of the resin has been found to be 2.0, 2.6, 1.6, 1.6, 2.6 and 1.8 mg g(-1) of resin for Cd, Co, Cu, Fe, Ni and Zn, respectively. The tolerance limits of electrolytes, NaCl, NaF, NaI, NaNO3, Na2SO4 and of cations, Mg2+ and Ca2+ in the sorption of the six metal ions are reported. The preconcentration factor was between 50 and 200. The t1/2 values for sorption are found to be 5.3, 2.9, 3.2, 3.3, 2.5 and 2.6 min for the six metals, respectively. The recoveries are between 96.0 and 100.0% for the different metals at preconcentration limits between 10 to 40 ng mL(-1). The preconcentration method has been applied to determine the six metal ions in river water samples after destroying the organic matter (if present in very large amount) with concentrated nitric acid (RSD < or = 8%, except for Cd for which it is upto 12.6%) and cobalt content of vitamin tablets with RSD of approximately 3.0%.