On-line separation and preconcentration of silver ion on amidino-thiourea immobilized glass beads packing in flow injection analysis with atomic absorption spectrometric detection.

Amidino-thiourea immobilized glass beads (AGB I) were prepared and used as the microcolumn packing for the flow injection (FI) on-line separation and preconcentration of Ag(I) coupled with atomic absorption spectrometry (AAS) determination. Base metal ions and anions with a concentration of 2.0 mg mL(-1) had no interference with the determination of Ag(I). The limit of detection (LOD) of Ag(I) for a preconcentration time of 60 s with a sampling flow rate of 5.0 mL min(-1) for 40.0 ng mL(-1) of Ag(I) were 0.50 ng mL(-1) with the peak-height absorbance mode and 1.26 ng mL(-1) with the peak-area absorbance mode, respectively. The relative standard deviations (RSD) of 7 replicate determinations were 0.9% and 0.7% for the peak-height absorbance (H) and the peak-area absorbance (A), respectively. The method was successfully applied to the determination of Ag(I) in ore samples.     

On-line ion-exchange preconcentration and determination of traces of platinum by electrothermal atomic absorption spectrometry

A method to determine trace amounts of platinum in different samples based on electrothermal atomic absorption spectrometry is described. The preconcentration step is performed on a chelating resin microcolumn [1,5-bis(2-pyridyl)-3-sulfophenyl methylene thiocarbonohydrazide (PSTH) immobilized on an anion-exchange resin (Dowex 1x8-200)] placed in the autosampler arm. The combination of a peristaltic pump for sample loading and the atomic absorption spectrometer pumps for elution through a selection valve simplifies the hardware. The peristaltic pump and the selection valve are easily controlled electronically with two switches placed in the autosampler, which are activated when the autosampler arm is down. Thus, the process is fully automated without any modification of the software of the atomic absorption spectrometer. Under the optimum conditions with a 60-s preconcentration time, a sample flow rate of 2.4 mL min(-1), and an injection volume of eluent of 40 microL, a linear calibration graph was obtained in the range 0-100 ng mL(-1). The enrichment factor was 14. The detection limit under these conditions is 1 ng mL(-1), and the relative standard deviation (RSD) is 1.6% for 10 ng mL(-1) of Pt. The method has been applied to the determination of platinum in catalyst, vegetation, soil, and natural water samples. The results showed good agreement with the certified value and the recoveries of Pt added to samples were 98-105%.     

Determination of Trace Lithium in Uranium Compounds by Adsorption on Activated Alumina Using a Micro-column Method

A novel method using a micro-column packed with active alumina as solid phase was proposed for separation of trace lithium from uranium compounds prior to determination. The method is based on a preliminary chromatographic separation of the total amount of uranium. This separation involves passing the solution containing sodium carbonate through active alumina and then eluting the trace lithium retained by the solid phase with a solution of sulfuric acid. Two modes, off-line and on-line micro-column preconcentration, were performed. In conjunction with atomic absorption spectrometry, this on-line preconcentration technique allows a determination of lithium at 10(-9) level. Both off-line and on-line mode operation conditions were investigated in separation and determination of trace lithium by micro-column method (length of column bed, flow rate, etc.). The adsorption capacity of activated alumina was found to be 343 microg g(-1) for lithium. Under the optimal operation condition, the detection limit (DL) of on-line preconcentration corresponding to three times the standard deviation of the blank (S/N = 3) was found to be 1.3 ng mL(-1) and the RSD of this method is 3.32% (n = 5). The on-line calibration graph was linear over the range 20 - 200 ng mL(-1). A good preconcentration factor 820 was achieved by experiment under the on-line mode. The developed method was applied to the analysis of trace lithium in nuclear grade uranium compounds.     

Potential of Modified Multiwalled Carbon Nanotubes with 1-(2-Pyridylazo)-2-naphtol as a New Solid Sorbent for the Preconcentration of Trace Amounts of Cobalt(II) Ion

The present paper reports on the application of modified multiwalled carbon nanotubes (MMWCNTs) as a new, easily prepared and stable solid sorbent for the preconcentration of trace Co(II) in aqueous solution. Multiwalled carbon nanotubes (MWCNTs) were oxidized with concentrated HNO(3) and modified with 1-(2-pyridylazo)-2-naphtol (PAN), and were then used as a solid phase for the preconcentration of Co(II). Factors influencing the sorption and desorption of Co(II) were investigated. Elution was carried out with 0.5 mol L(-1) HNO(3). The amount of eluted Co(II) was measured using flame atomic absorption spectrometry. The effects of the experimental parameters, including the sample pH, sample flow rate, eluent flow rate and eluent concentration, were investigated. The effect of coexisting ions showed no interference from most ions tested. The proposed method permitted a large enrichment factor (about 300). The precision of the method was 1.63% (for eight replicate determination of 0.5 microg mL(-1) of Co(II)) and the limit of detection was 0.55 ng mL(-1). The method was applied to the determination of Co(II) in water, biological and standard samples.     

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.     

Hydride generation atomic absorption spectrometric determination of bismuth after separation and preconcentration with modified alumina

A simple and sensitive method has been developed for the trace determination of bismuth in aqueous samples by a combination of solid‐phase extraction and hydride generation atomic absorption spectrometry. The method is based on the use of a column packed with 2‐mercaptobenzothiazole immobilized on sodium dodecyl sulfate coated alumina. Different parameters influencing the separation and preconcentration of bismuth such as pH, sample volume, type, and concentration of eluent, and the flow rate of sample and eluent were studied. A sample volume of 500.0 mL resulted in a preconcentration factor of 100. The precision (relative standard deviation, N = 10) at the 300 ng/L level and the limit of detection (3s) were found to be 2.3% and 12 ng/L, respectively. The developed method was successfully applied to the determination of bismuth in natural water samples and two certified reference materials.     

Cloud point extraction preconcentration of manganese(II) from natural water samples using 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone and triton X-100 and determination by flame atomic absorption spectrometry.

The possibility was investigated by using 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP) as the chelating reagent for separation and preconcentration of manganese(II) by cloud point extraction (CPE) and subsequent determination by flame atomic absorption spectrometry (FAAS). The effects of experimental conditions such as pH, concentration of chelating agent and surfactant, equilibration temperature and time on cloud point extraction were studied. Under the optimum conditions, preconcentration of 10 ml of sample solution permitted the detection of 1.45 ng mL(-1) of manganese with an enrichment factor of 20. The proposed method was applied to the determination of trace manganese in water samples with satisfactory results.     

Determination of trace amounts of Pd(II) ions in water and road dust samples by flame atomic absorption spectrometry after preconcentration on modified organo nanoclay

This paper describes the application of organo nanoclay, an easily prepared and stable solid sorbent, to the preconcentration of trace amounts of palladium ions in aqueous solution. The organo nanoclay was prepared by adding tetradecyldimethylbenzylamonium chloride onto montmorillonite, which was then modified with 1-(2-pyridylazo)-2-naphthol. The modified nanoclay was used as a solid sorbent for separation and preconcentration of trace amounts of Pd(II) ions, and a simple, sensitive, and economical method was developed for determination of trace amounts of palladium by flame atomic absorption spectrometry. The sorption of Pd(II) ions was quantitative in the pH range of 1.5-5.0, whereas quantitative desorption occurred with 5.0 mL of a mixture containing 1.0 M thiourea and 1.0 M HCl. The RSD of the method was +/- 2.1% (n = 10; concn = 0.5 microg/mL), and the LOD (3sigma(bl); sigma = SD and bl = blank) was 0.1 ng/mL. The calibration curve was linear for concentrations of 0.5-8.0 microg/mL in the initial solution, and the preconcentration factor was 140. The maximum capacity of the sorbent was 2.4 mg Pd(II)/g modified organo nanoclay. The influences of the experimental parameters, including sample pH, eluant volume, eluant type, sample volume, and interfering ions, on the recoveries of the palladium ion were investigated. The proposed method was applied to the preconcentration and determination of palladium in different samples.     

Application of flow injection on-line electrothermal atomic absorption spectrometry to the determination of rhodium

A fully automated procedure for the determination of rhodium has been developed using flow injection (FI) on-line microcolumn preconcentration coupled with electrothermal atomic absorption spectrometry (ETAAS). The proposed FI manifold and its operation make possible the introduction of the total eluate volume into the graphite atomizer, avoiding the necessity for optimisation of subsampling the eluate. Rhodium is adsorbed on a microcolumn packed with 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel (DPTH-gel). Under the optimum conditions, using a 60 s preconcentration time, a sample flow rate of 3.5 mL min(-1) and an injection volume of eluent of 50 microL, a linear calibration graph was obtained from 1 to at least 40 ng mL(-1) and the detection limit was 1 ng mL(-1). The proposed method has been successfully applied to the analysis of samples. Its performance was investigated against certified reference catalyst sample SRM-2557 and by recovery measurements on spiked samples (soil, foods and beverages).     

Cloud-point formation based on mixed micelles for the extraction, preconcentration and spectrophotometric determination of trace amounts of beryllium in water samples.

A cloud-point extraction process using a mixed micelle of the cationic surfactant cetyl pyridinium chloride (CPC) and non-ionic surfactant Triton X-114 to extract beryllium from aqueous solutions was investigated. The method is based on the color reaction of beryllium with Chrome Azurol S (CAS) in acetate buffer and the mixed micelle-mediated extraction of the complex. This complex was concentrated in a surfactant-rich phase after separation. The optimal extraction and reaction conditions (e.g. pH, reagent and surfactant concentrations, temperature, incubation and centrifuge times) were evaluated and optimized. Under the optimized conditions, the analytical characteristics of the method (e.g. limit of detection, linear range and preconcentration factor) were obtained. Linearity was obeyed in the range of 0.30 - 18 ng mL(-1) of beryllium and the detection limit of the method was 0.05 ng mL(-1). The interference effect of some cations and anions was also studied. The proposed method was successfully applied to the determination of beryllium in real water samples.     

Interference-free determination of trace levels of gold and palladium in geological and metallurgical samples by flame atomic absorption spectrometry coupled with a flow injection on-line microcolumn preconcentration and separation system

A simple and highly selective method was developed for the routine determination of trace or ultratrace amounts of gold and palladium in geological and metallurgical samples. The method uses flow injection on-line preconcentration and separation with determination by flame atomic absorption spectrometry. Au and Pd in the sample are adsorbed on a 2-mercaptopyrimidine chemically modified silica gel (MPMSG) packed microcolumn in a 0.50M HCl medium and then eluted with 0.5 or 1.0% thiourea solution. The eluates are introduced into the flame atomic absorption spectrometer directly. With the use of a 0.85 mL microcolumn (about 0.14 g MPMSG packed), the present system tolerated concentrations of common base metal ions up to 25.0 mg/mL and concentrations of anions up to 100.0 mg/mL when Au(III) at 0.100 microg/mL and Pd(II) at 0.200 microg/mL were preconcentrated for 60 s with a sample flow rate of 5.0 mL/min. The limits of detection were 3.1 ng/mL for Au(III) and 6.1 ng/mL for Pd(II) with relative standard deviations of < or = 2.5%. The analytical results obtained by the proposed method for geological and metallurgical samples were in good agreement with the certified values.     

Field preconcentration of cadmium from seawater by using a minicolumn packed with Amberlite XAD-4/4-(2-pyridylazo) resorcinol and its flow-injection-flame atomic absorption spectrometric determination at the ng L(-1) Level

A flow injection analysis-flame atomic absorption spectrometric method for the determination of cadmium in seawater was developed with the aim of yielding a sensitive assay with a low detection limit. The method employs a field flow preconcentration technique involving a minicolumn containing Amberlite XAD-4 impregnated with the complexing agent 4-(2-pyridylazo) resorcinol. A Plackett-Burman 2(7)x3/32 design for seven factors (sample pH, sample flow rate, eluent volume, eluent concentration, eluent flow rate, ethanol percentage in the eluent and minicolumn diameter) was carried out in order to find the significant variables affecting the field continuous preconcentration system (FCPS) and the flow injection elution manifold for cadmium determination in seawater samples by flame atomic absorption spectrometry. Cadmium can be preconcentrated with an enrichment factor of 1053 for a sample volume of 200 mL and a preconcentration time of 57 min. In these experimental conditions, the method provides a linear relationship between absorbance and cadmium concentration in the range from 22-1900 ng L(-1), with a detection limit (3SD) of 6 ng L(-1). The precision (expressed as relative standard deviation) for eleven independent determinations reached values of 8.9-0.8% in cadmium solutions of 50-700 ng L(-1). Analysis of certified reference materials (SLEW-3 and NASS-5) showed good agreement with the certified value. This procedure was applied to the determination of cadmium in seawater from Galicia (Spain).     

Determination of Ultratrace Amounts of Copper(Ⅱ) in Water Samples by Electrothermal Atomic Absorption Spectrometry After Cloud Point Extraction

A novel approach was developed for the determination of ultratrace amounts of copper in water samples by using electrothermal atomic absorption spectrometry (ETAAS) after cloud point extraction (CPE). 1-( 2-Pyridylazo)-2-naphthol was used as the chelating reagent and Triton X-114 as the micellar-forming surfactant. CPE was conducted in a pH 8.0 medium at 40 ℃ for 10 min. After the separation of the phases by centrifugation, the surfactant-rich phase was diluted with 1 mL of a methanol solution of 0. 1 mol/L HNO3. Then 20 μL of the diluted surfactant-rich phase was injected into the graphite furnace for atomization in the absence of any matrix modifier. Various experimental conditions that affect the extraction and atomization processes were optimized. A detection limit of 5 ng/L was obtained after preconcentration. The linear dynamic range of the copper mass concentration was found to be 0-2.0ng/mL, and the relative standard deviation was found to be less than 3.1% for a sample containing 1.0 ng/mL Cu(Ⅱ). This developed method was successfully applied to the determination of ultratrace amounts of Cu in drinking water, tap water, and seawater samples.     

Determination of ultratrace elements in natural waters by solid-phase extraction and atomic spectrometry methods

A study was carried out on the preconcentration of ultratrace amounts of cadmium, lead, manganese, copper and iron from high-salinity aqueous samples and determination by atomic spectrometry methods. Sample volume, amount of resin, loading flow rate, and elution volume were optimized in order to obtain the simultaneous preconcentration of all the analytes. Quantitative recoveries were obtained by using 200 mg of iminodiacetic resin with a loading flow rate of 2 mL min(-1), elution volume of 3 mL and sample volume of 50-450 mL. Only copper in seawater samples was not completely retained by the resin (60-70% recovery), due to unfavorable competition of iminodiacetic-active groups with organically bound metal.To quantify the metals in the eluates, two atomic spectrometry techniques were compared: electrothermal atomization atomic absorption spectrometry (ETAAS) and inductively coupled plasma-optical emission spectrometry (ICP-OES) with simultaneous CCD detection system. Both techniques are suitable for sample analysis with detection limits of 1.0, 4.7, 3.3, 6.8, and 53 ng L(-1) using ETAAS and 12, 122, 3.4, 17, and 21 ng L(-1) using ICP-OES for Cd, Pb, Mn, Cu, and Fe, respectively. Relative standard deviations of the procedures ranged from 1.7 to 14% at the sub-microg L(-1) concentration level. The accuracy of both methods was verified by analyzing various certified reference materials (river water, estuarine water, coastal and off-shore seawater).     

Application of multiwalled carbon nanotubes as solid phase extraction sorbent for preconcentration of trace copper in water samples

The adsorption behavior of multiwalled carbon nanotubes (MWNTs) toward copper has been investigated systemically, and a new method has been developed for the determination of trace copper in water samples based on preconcentration with a microcolumn packed with MWNTs prior to its determination by flame atomic absorption spectrometry. The optimum experimental parameters for preconcentration of copper, such as pH of the sample, sample flow rate and volume, elution solution and interfering ions, have been investigated. Copper can be quantitatively retained by MWNTs in the pH range 5-8, and then eluted completely with 0.5 M HNO3. The detection limit of this method for Cu was 0.42 ng/mL, and the RSD was 3.5% at the 10 ng/mL Cu level. The method was validated using a certified reference material, and has been successfully applied for the determination of trace copper in water samples.     

Flow Injection Semi-online Preconcentration Graphite Furnace Atomic Absorption Spectrometry for Determination of Cadmium, Copper and Manganese

IntroductionGraphite furnace atomic absorption spectrome-try (GFAAS) is one of the most sensitive tech-niques for the determination of various elementswith detection limits in the range ofμg/ L to ng/ L.Despite the impressive detection power of the tech-nique,GFAAS can tbe routinely used to make di-rect analysis of some real samples with complexcomposition[1] . This is due to the matrix interfer-ence and/ or insufficient detection power. Conse-quently,separation and preconcentration proc…     

Determination of picomolar beryllium levels in seawater with inductively coupled plasma mass spectrometry following silica-gel preconcentration

A robust and rapid method for the determination of natural levels of beryllium (Be) in seawater was developed to facilitate mapping Be concentrations in the ocean. A solid-phase extraction method using a silica gel column was applied for preconcentration and purification of Be in seawater prior to determination of Be concentrations with inductively coupled plasma mass spectrometry (ICP-MS). Be was quantitatively adsorbed onto silica gel from solutions with pH values ranging from 6.3 to 9, including natural seawater. The chelating agent ethylenediamine tetraacetic acid was used to remove other ions in the seawater matrix (Na, Mg, and Ca) that interfere with the ICP-MS analysis. The reproducibility of the method was 3% based on triplicate analyses of natural seawater samples, and the detection limit was 0.4 pmol kg⁻¹ for 250 mL of seawater, which is sufficient for the analysis of seawater in the open ocean. The method was then used to determine the vertical profile of Be in the eastern North Pacific Ocean, which was found to be a recycled-type profile in which the Be concentration increased with depth from the surface (7.2 pmol kg⁻¹ at <200 m) to deep water (29.2 pmol kg⁻¹ from 3500 m to the bottom).     

Atomic absorption spectrometric determination of trace zinc in alloys and biological samples after preconcentration with [1-(2-pyridylazo)-2-naphthol] on microcrystalline naphthalene

An atomic absorption spectrometric method for the determination of trace amounts of zinc after adsorption of its [1-(2-pyridylazo)-2-naphthol] complex on microcrystalline naphthalene has been developed. This complex is adsorbed on microcrystalline naphthalene in the pH range 3.5-7.5 from large volumes of aqueous solutions of various alloys and biological samples with a preconcentration factor of 40. After filtration, the solid mass consisting of the zinc complex and naphthalene was dissolved with 5 ml of dimethylformamide and the metal was determined by flame atomic absorption spectrometry. Zinc can alternatively be quantitatively adsorbed on [1-(2-pyridylazo)-2-naphthol]-naphthalene adsorbent packed in a column and determined similarly. About 0.5 ng of zinc can be concentrated in a column from 200 ml of aqueous sample, where its concentration is as low as 2.5 pg ml-1. The calibration curve is linear in the range 0.1-6.5 ng ml-1 in dimethylformamide solution. Eight replicate determinations of 2 ng ml-1 of zinc gave a mean absorbance of 0.145 with a relative standard deviation of 1.5%. The sensitivity for 1% absorption was 0.061 ng ml-1. Various parameters, such as the effect of pH and the interference of a number of metal ions on the determination of zinc, have been studied in detail to optimize the conditions for the determination of zinc in various standard complex materials.     

Solid phase extraction and flame atomic absorption spectrometric determination of trace amounts of cadmium and lead in water and biological samples using modified TiO2 nanoparticles

A solid phase extraction procedure for the separation and preconcentration of trace amounts of Cd(II) and Pb(II) using the alizarin red S modified TiO₂ nanoparticles prior to their determination by flame atomic absorption spectrometry has been proposed. The influences of some analytical parameters such as pH, flow rates of sample and eluent, type and concentration of the eluent, and interfering ions on the recovery of Cd(II) and Pb(II) by the sorbent were investigated. The analytes were quantitatively sorbed from the aqueous solution at pH 5.5 onto a microcolumn packed with the sorbent and recovered with 2.0?mL of 1.5?mol?L^?1 hydrochloric acid. Under the optimum experimental conditions, the detection limits for Cd(II) and Pb(II) were 0.11 and 0.30?ng?mL^?1 and the relative standard deviations for ten replicate measurements of 5.0 and 50.0?ng?mL^?1 of Cd(II) and Pb(II) were 2.1 and 1.9%, respectively. A sample volume of 200?mL resulted in a preconcentration factor of 100. The method was successfully applied to the determination of Cd(II) and Pb(II) in water and biological samples, and accuracy was examined by the recovery experiments, independent analysis using electrothermal atomic absorption spectrometry, and analysis of a water standard reference material (SRM 1643e).     

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.