Flame atomic absorption analysis for selenium after electrochemical preconcentration

Selenium(IV) is determined in the presence of 3.5% sodium chloride by electrochemical preconcentration on a platinum spiral, prior to flame atomic absorption analysis. The electrodeposition is carried out in the presence of hydrazine dihydrochloride to prevent the generation of chlorine at the counter electrode; chlorine oxidizes selenium(IV) to the non-reducible selenium(VI) ion. A detection limit of 5 ppb and an electrolysis efficiency of 10% were obtained for a 25-ml sample and a 5-min electrolysis time. The absolute detection limit was 10 ng.     

Semipermeable ion-exchange membranes as a preconcentration matrix for trace analysis by electrochemical and neutron-activation techniques

Ion-exchange membranes were used in conjunction with neutron-activation analysis and anodic stripping voltammetry for the determination of certain trace metal ions. The various parameters which govern the applicability, limitations and sensitivity of the methods were investigated. A new membrane "barrier" electrode assembly was introduced and found to be useful for the anodic stripping determination of trace metal ions in the presence of surface active materials.     

POLYORGS as complexing sorbents for preconcentration of trace metals

Summary The main characteristics of the complexing sorbents POLYORGS are reviewed. These sorbents contain pyrazole, imidazole, amidoxime, 2-mercaptobenzothiazole, thioglycolanilide and arsenazo groups and exhibit high selectivity in respect to noble, rare-earth and heavy metals. The sorbents POLYORGS are applied for the preconcentration of these metals to be determined in ores, rocks, natural and waste waters, and industrial products. The metal determinations after preconcentration are carried out by means of different instrumental methods (e.g., AAS, XRFA, ICP-AES, NAA) either directly in the sorbent, after elution of the analytes or decomposition of the sorbent.     

Determination of trace heavy metals in waters by flame atomic absorption spectrometry after preconcentration with 2,4-dinitrophenyldiazoaminoazobenzene on Amberlite XAD-2

A new column, solid-phase extraction (SPE), preconcentration method was developed for determination of Cd, Co, and Cu ions in natural water samples by flame atomic absorption spectrometry. The procedure is based on the retention of analytes in the form of 2,4-dinitrophenyldiazoaminoazobenzene (DNDAA) complex on a mini column of DNDAA-XAD-2 resin. The effects of pH, eluent type, eluent concentration, eluent volume, resin quantity, sample volume, sample flow rate, and matrix ions (Na, Ca, and Mg) were investigated on the recovery of the metals using model solutions. The detection limit for Cd, Co, and Cu was 0.062, 0.084, and 0.057 μg L⁻¹ and the quantification limit was 0.17, 0.24, and 0.12 μg L⁻¹ respectively. The method was validated by the analysis of a certified reference material with the results being in agreement with those quoted by manufactures. The developed method was applied to the determination of trace metal ions in tap water, river water samples with satisfactory results.     

Simultaneous multi-element analysis for trace metals in sea water by inductively-coupled plasma/atomic emission spectrometry after batch preconcentration on a chelating resin

Batch treatment with Chelex-100 resin was investigated for preconcentration of trace metals in sea water followed by determination by inductively-coupled plasma atomic emission spectrometry. The preconcentration conditions such as resin weight, stirring time, and amount of ammonium acetate buffer solution were carefully examined for effective multi-element preconcentration from sea water. The resin weight could be decreased to 0.5 g (dry weight) for 1 l of sea water, which was much less than that required in the column method, and a preconcentration factor of 100 was achieved. Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Y, Mo, Cd and Pb in sea water were measured with good precision. The detection limits ranged from 6 to 180 ng l^?1. The time required for one sample by the batch method was only 3 h.     

Comparison of preconcentration procedures for trace metals in natural waters

The relative merits of eight procedures for preconcentrations of trace metal ions from natural water samples and synthetic solutions are evaluated. Spikes (100 μg l^?1 ) of Mn, Co, Zn, Eu, Cs and Ba and the corresponding radioactive tracers were added to batches of drinking water, estuarine water, sea water, ground water, twice-distilled water and ahumic material solution. After equilibration for 2–5 months, the following techniques were applied: passage through columns of Dowex Al chelating resin and ofsilylated silica gel, filtration through laminate membrane filters and chelating diethylenetriamine cellulose filters, precipitation with sodium diethyldithiocarbamate and l-(2-pyridylazo)-2-naphthol, extraction with ammonium pyrrolidinedithiocarbamate, and chelation by 8-quinolinol (oxine) followed by adsorption on activated carbon. The quantitative characteristics of these techniques and the influence of the water matrix effects are discussed, as well as the applicability for x-ray fluorescence analysis.     

Graphite furnace atomic absorption analysis of marine samples for trace metals

Trace element determinations by graphite furnace atomic absorption spectrometry which are pertinent to the analysis of marine samples are highlighted. Results for the direct introduction of solids, slurries and dissolved samples of fauna, sediments and saline waters are discussed. Examples drawn from recent literature show that typical samples which benefit most from direct solid sampling are those that do not require the very highest accuracy or precision. No clear consensus amongst users of this technique has emerged regarding the choice between peak height or area recording or the need to standardize by aqueous calibration, the method of additions or use of matrix matched solids. Slurry sampling overcomes several limitations associated with direct solid sampling and whereas generalizations serve little purpose in assessing the applicability of the direct solid sampling approach, slurry sampling holds great promise for widespread use. Examples of external and in situ concentration techniques necessary to augment the relative detection power of the system for the analysis of saline waters are also given. These include an examination of “classical” procedures utilizing chelation-solvent extraction, immobilized ligands and precipitation methods as well as techniques which rely on sequestration in the furnace of volatile analyte species generated in external cells.     

Atomic absorption spectrometry of selenium in an argon-hydrogen flame after electrochemical preconcentration

Different methods of atomization of selenium from a platinum wire filament are described, including electrothermal heating of the filament and atomlzation in an argon-hydrogen flame. A combination of these approaches proved to give the best sensitivity and detection limit. The selenium was preconcentrated on the filament by electrolysis prior to the atomic absorption measurements to eliminate chemical interferences and improve the sensitivity of the method. The detection limit was 0.5 μg l^-1 for a 5-min electrolysis, and 0.2 μg l^-1 when the electrolysis time was 30 min.     

Determination of selenium in a nickel alloy by flame atomic absorption spectrometry after electrochemical preconcentration

The nickel alloy is dissolved in nitric/hydrochloric/phosphoric acid mixture, and selenium is electrodeposited onto a platinum loop at ?0.4 V (vs. Ag/AgCl). Selenium is atomized from the electrode in an argon/hydrogen flame with simultaneous electrothermal heating of the loop. For the NBS standard nickel-based high-temperature alloy (SRM 899), the mean value found was 9.7 μg g^?1 with a standard deviation of 0.4 μg g^?1 (certified value 9.5 ± 0.1).     

Determination of some trace metals in waters by flame atomic absorption spectrometry after preconcentration on Amberlite XAD-16 resin with sodium tetraborate

A method was described for the determination of the elements Cr, Mn, Fe, Co, Ni, Cu, Cd, Pb, and Bi in waters by flame atomic absorption spectrometry (FAAS) after separation and preconcentration on Amberlite XAD-16 resin with sodium tetraborate using a chromatographic column. Parameters influencing the analytical performance, including pH and the volume of sample, amount of analyte and interfering effect of co-existing ions, were studied in detail. The recovery values were quantitative (> or = 95%), and the relative standard deviation (RSD) and detection limit (DL) varied in the range of 1.1-2.4% (n=10) and 0.002-0.177 microg m(-1) (3s, n=20), respectively. After being optimized, the proposed method was applied to the drinking water, waste water and artificial sea water samples. Recovery values of the elements investigated, were quantitative for tap water and synthetic sea water, except for Mn, Co and Ni (including also Cd for synthetic sea water). Recovery values of Cd, Pb, Cu and Co were found to be 95, 102, < or = 87, and < or = 83%, respectively, for the waste water samples.     

On-line electrochemical preconcentration of manganese for graphite furnace atomic absorption spectrometry using a flow-through electrochemical cell

A flow system incorporating a 2-electrode electrochemical microcell with a working electrode made from crushed reticulated vitreous carbon and a graphite furnace AAS instrument was used for the preconcentration and determination of trace amounts of Mn. The sample, rinsing and elution solutions were pneumatically transported through the system. Mn²⁺ ions can be quantitatively deposited both anodically and cathodically at a voltage of +1.5 to + 3 V and –2.5 to –4V, respectively applied to the cell. Samples of 0.1 to 1 ml volume were analyzed within 5–10 min. The limits of detection and determination were 8.7 and 29 pg, respectively. The reproducibility was 1.5 to 5%. The electrochemical behaviour of Mn in the flow system was studied by using a 3-electrode flow-through cell coupled on-line to a flame AAS instrument.On leave from Department of Analytical Chemistry, Slovak Technical University, CS-812 37 Bratislava, Czechoslovakia     

Electrolytical microcell for on-line preconcentration of trace metals in flow systems

Summary The separation of trace metals from solutions of electrolytes by electrodeposition in a 30 l electrolytical flow-through cell was studied. The working electrode of the flow cell was made from powdered spectral or glassy carbon. The electrodeposition is complete for Cu²⁺, Cd²⁺, Mn²⁺ and Pb²⁺, partial for Zn²⁺, Fe³⁺ and Ni²⁺. Mn²⁺ and Pb²⁺ can also be deposited by anodic oxidation on the working electrode. The deposition is complete up to sample flow rates of 3–4 ml/min. The deposited elements are dissolved by short-circuiting the electrodes and flushing the cell with diluted acid. The dissolved elements are determined on-line by flame AAS. Data evaluation through peak area measurement is discussed.     

Determination of trace metals in seawater by graphite furnace atomic absorption spectrometry with preconcentration on silica-immobilized 8-hydroxyquinoline in a flow-system

Summary A flow-system utilizing a miniature column packed with silica-immobilized 8-hydroxyquinoline (I-8-HOQ) was used for the preconcentration of Cd, Pb, Zn, Cu, Fe, Mn, Ni, and Co from seawater prior to their determination by graphite furnace atomic absorption spectrometry (GFAAS). Enrichment factors sufficient to permit the analysis of an open ocean seawater reference material using 50 ml sample volumes (100 ml for Co determinations) were obtained. Recoveries of the above elements from seawater averaged 93% (range 87–97%) with absolute blanks ranging between 0.04 ng (Ni) and 4.0 ng (Fe). Estimated detection limits for these elements vary from 0.2 ng l^–1 (Co) to 40 ng l^–1 (Fe) based on a 50 ml sample volume (100 ml for Co).

---

Bestimmung von Spurenmetallen in Meereswasser durch Graphitofen-AAS mit Anreicherung an Kieselgel-immobilisiertem 8-Hydroxychinolin in einem Durchflu\system

     

Exploding wire excitation for trace analysis of Hg, Cd, Pb and Ni using electrodeposition for preconcentration

The use of exploding silver wires for spectrochemical excitation is described. The apparatus used in these studies is discussed along with the electrical and radiative properties of exploding silver wires. The use of controlled-potential electrodeposition onto silver wires for sample introduction is considered. Experimental parameters for electrodeposition and exploding-wire excitation are presented. Cd, Ni, Hg and Pb are considered for analysis and show absolute detection limits of 10 ng, 10 ng, 30 ng and 15 ng, respectively. These amounts of material on the wire represent relative detection limits of 0.001 ppm, 0.002 ppm, 0.003 ppm and 0.001 ppm respectively in the analytical solutions. The exploding wire excitation method exhibits minimal matrix dependency and good reproducibility. Percent relative standard deviations for Cd, Ni, Hg and Pb are ±17.3%, ±16.6%, ±26.5% and ±12.4%, respectively. Sample introduction by controlled-potential electrodeposition offers not only a convenient means of preconcentrating trace metals from solution but also the possibility of selectively plating one element in the presence of a large excess of other elements in solution.     

Multielement preconcentration of trace heavy metals in seawater with an emulsion containing 8-quinolinol for graphite-furnace atomic absorption spectrometry

A water-in-oil type emulsion containing 8-quinolinol has been used for the concentration of traces of heavy metals from seawater prior to their determinations by graphite-furnace atomic absorption spectrometry. The emulsion used was prepared by dissolving 40 mg of 8-quinolinol and 60 mg of sorbitan monooleate (Span-80) in 3.0 ml of toluene and vigorously mixing with 0.70 ml of aqueous hydrochloric acid solution (1.5 mol l⁻¹) by ultrasonic irradiation. The resulting emulsion was gradually injected into 100 ml of sample solution (pH 8.5) and dispersed by stirring as numerous tiny globules. Four heavy metals (Co, Ni, Cu, and Cd) in the sample solution were quantitatively transported through the organic layer into the acidic aqueous droplets encapsulated in the emulsion. After collecting the dispersed emulsion globules, they were demulsified by heating and the heavy metals in the segregated aqueous phase were determined by atomic absorption spectrometry. Owing to the highly efficient concentration (100-fold), these heavy metals at sub-ng ml⁻¹ levels in seawater were determined with satisfactory accuracy and precision, being confirmed with certified reference samples.     

Chelating polymers and related supports for separation and preconcentration of trace metals

This review is concerned mainly with the applications of chelating polymeric resins for the separation and concentration of trace metals from oceans, rivers, streams and other natural systems. Commercially available resins, specially prepared polymers and a selection of other sorbents are described and their uses outlined. Special emphasis is placed on the preconcentration of uranium from sea-water.     

Flame atomic absorption determination of trace amounts of cadmium after preconcentration using a thiol-containing task-specific ionic liquid

Dispersive liquid-liquid microextraction (DLLME) based on a task-specific ionic liquid (TSIL) was developed for the extraction and preconcentration of trace amounts of cadmium from aqueous samples, followed by flame atomic absorption spectrometry (FAAS) determination. In the proposed approach, cadmium ions are extracted from aqueous samples using small volumes of trioctylmethylammonium thiosalicylate (TOMATS) dissolved in acetone. TOMATS is a thiol-containing TSIL that can form metal thiolate complexes due to the chelating effect of the ortho-positioned carboxylate group relative to the thiol functionality. The main parameters affecting the performance of DLLME based on TSIL, such as pH, amount of TOMATS, extraction time, injection volume, salt addition, and centrifugation time, were optimized. Under optimum conditions, an LOD of 1.16 ng/mL and a good RSD of 1.8% at 60.0 ng/mL were obtained (n=7). The proposed method was applied to tap water, wastewater, well water, and milk samples. The results showed that DLLME based on TSIL combined with FAAS is a rapid, simple, sensitive, selective, low cost, volatile organic solvent-free, and efficient analytical method for the separation and determination of trace amounts of cadmium ions.     

On-line preconcentration and GFAAS determination of trace metals in waters

An on-line separation preconcentration system coupled to electrothermal (graphite furnace) atomic absorption spectrometry was developed. A miniature column packed with iminodiacetic acid ethyl cellulose (IDAEC) was inserted into the loop. A peristaltic pump was used to deliver solutions. A flow of air was driven into the packed column, evacuating it between sample loading, washing and elution. The retained analyte was introduced on-line to graphite furnace using countercurrent elution with HNO₃. The system was applied for the determination of V, Co and Pb in medicinal mineral water samples, and nickel in sea water samples. The detection limits (3σ) were 0.058, 0.022, 0.067, 0.062 μg/l for Co, Pb, V, and Ni, respectively. The R.S.D. (n=5) was <5% at 0.4–1.0 μg/l concentration range.     

On-line preconcentration and ICP determination for trace metal analysis

The use of a closed-loop on-line enrichment procedure in combination with an ICP plasma emission spectrometer has been developed for the analysis of trace metal ions, such as Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn. The procedure utilizes a preconcentration column filled with an anion exchange resin and 8-hydroxy-7-iodoquinoline-5-sulphonic acid is added to the sample prior to preconcentration. Details on the optimization of pretreatment and instrumental conditions are described. Results obtained for the analysis of river water and antarctic seawater are reported.Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria