On-line preconcentration with different solid adsorbents for lead determination

An on-line column preconcentration method based on the combined use of ammonium O,O-diethyldithiophosphate and activated carbon or polyurethane foam as adsorbents has been developed for the determination of Pb in water samples. The complexed Pb was eluted with ethanol and determined by flame atomic absorption spectrometry. The optimum preconcentration conditions are given for each adsorbent. The enrichment factors were 63 and 294, and the detection limits (3σ) 3?μg?L^–1 and 0.8?μg?L^–1, respectively, for the carbon and foam systems. When the optimized procedures were applied to the determination of Pb in water samples the recovery efficiency was > 96%.     

On-line sorbent extraction, preconcentration and determination of lead by atomic absorption spectrometry

A method for the quantitative preconcentration of lead based on an existing batch process was developed for implementation in a flow system including a flame AAS detector. Lead can be quantitatively preconcentrated as pyrrolidinedithiocarbamate or dithizonate on an activated carbon minicolumn. The chelates are eluted in methyl isobutyl ketone and introduced directly into the nebuliser-burner. An enrichment factor of 50 is typically obtained for a preconcentration time of 2 min (lead can be determined at concentrations between 15 and 400 ng/ml), which results in a throughput of ca. 25 samples per hr. The sensitivity achieved with the two reagents is similar, but the selectivity provided by APDC exceeds that of dithizone. Based on the results obtained in the determination of lead in reference materials (minerals and skim milk), the proposed APDC method is applicable to real samples.     

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     

On-line solid phase extraction coupled to ICP-OES for simultaneous preconcentration and determination of some transition elements

An on-line solid phase extraction method coupled to ICP-OES was developed for the simultaneous determination of Ce(III), La(III), Sm(III), Y(III), Yb(III), Dy(III), Hf(IV), Zr(IV) and Th(IV) ions in aqueous samples. The ions forming hydrophobic complexes with 3,5,7,2?,4?-pentahydroxy flavone (morin) and were retained on an octadecyl silica (C₁₈) minicolumn. The adsorbed chelates were subsequently eluted from the column and directly transferred into the plasma with 80% (v/v) propanol:H₂O solution for the simultaneous determination of the metal ions. Different parameters affecting the ICP-OES signal intensities and extraction efficiency including pH of the solution, concentration of the chelating agent, flow rate and type of the eluent, loading rate and ionic strength were evaluated and optimized. The calibration graphs were linear in the range of 0.2–100 μg L^?1 and limit of detections for the extraction and determination of the ions in the aqueous sample (25 mL) were in the range 0.10–0.46 μg L^?1. The enhancement factors of the method for the metal ions obtained were in the range of 23 to 242 (V _Sample?=?25 mL) and the precision expressed as relative standard deviations (RSD %) was below 6.9%. Finally, the method was successfully applied to determine the target analytes in natural water samples.     

On-line complexation/preconcentration system for the determination of lead in wine by inductively coupled plasma-atomic emission spectrometry with ultrasonic nebulization

An on-line lead preconcentration and determination system implemented with inductively coupled plasma-atomic emission spectrometry (ICP-AES) with ultrasonic nebulization (USN) in association with flow injection was studied. For the preconcentration of lead, a Pb-quinolin-8-ol complex was formed on-line at pH 6.8 and retained on Amberlite XAD-16 resin. The lead was removed from the microcolumn by countercurrent elution with nitric acid. A total enhancement factor of 225 was obtained with respect to ICP-AES with pneumatic nebulization (15.0 for USN and 15.0 for the column). The detection limit for Pb for the preconcentration of a 10 mL wine sample was 0.15 microg/L. The precision for 10 replicate determinations at a Pb level of 25 microg/L was a relative standard deviation of 2.5%, calculated from the peak heights obtained. The calibration graph obtained by using the preconcentration system for lead was linear with a correlation coefficient of 0.9995 for levels near the detection limit up to > or = 1000 microg/L. The method was successfully applied to the determination of lead in wine samples.     

On-line coupling of electrochemical preconcentration in tungsten coil electrothermal atomic absorption spectrometry for determination of lead in natural waters

A flow injection system was coupled to a tungsten coil electrothermal atomizer (150 W) for on-line separation and preconcentration of lead based on its electrochemical reduction on the atomizer surface. The electrochemical cell is built up inside the furnace by using a Pt flow-through anode and the atomizer itself as the flow-through cathode. The manifold and the tungsten coil power supply were controlled by a computer running a program written in Visual Basic, which was utilized in synchronism with the original software of the atomic absorption spectrometer. The flow-through anode (50 mm long, 0.7 mm i.d.) was inserted in tip of the autosampler arm by replacing the last section of the PTFE sample delivering tube. The tungsten coil atomizer and the counter electrode were easily connected to a d.c. power supply. An enrichment factor of 25 was obtained for lead after a 120-s electrodeposition for a sample flowing at 1.0 ml min⁻¹. The method detection limit was 0.2 μg l⁻¹ Pb and the R.S.D.<5% (n=10 for 5 μg l⁻¹ Pb). Up to 2% m/v NaCl or KCl and 5% m/v CaCl₂ or MgCl₂ did not interfere on the separation and atomization of 5 μg l⁻¹ Pb.     

On-line preconcentration for capillary electrophoresis-atomic fluorescence spectrometric determination of arsenic compounds

An on-line preconcentration method was developed for capillary electrophoresis (CE) with hydride generation-atomic fluorescence spectrometric (HG-AFS) detection of arsenite, arsenate, dimethylarsenic acid, and monomethylarsenic acid. These arsenic species were negatively charged in the sample solution with high pH. When the potential was applied to the electrophoretic capillary, the negatively charged analyte ions moved faster and stacked at the boundary of sample and CE buffer with low pH. So, high sample pH in combination with low buffer pH allowed the injection of large sample volumes (approximately 1100 nL). Comparison of the preconcentration of analyte solution, prepared with doubly deionized water and that prepared with lake or river water, indicated that preconcentration was independent on the original matrix. With injection of approximately 1100 nL sample, an enrichment factor of 37-50-fold was achieved for the four species. Detection limits for the four arsenic species ranged from 5.0 to 9.3 microg.L(-1). Precisions (RSDs, n = 5) were in the range of 4.9-6.7% for migration time, 4.7-11% for peak area, and 4.3-7.1% for peak height, respectively. The recoveries of the four species in locally collected water solution spiked with 0.1 microg.mL(-1) (as As) ranged from 83 to 109%.     

A sensitive spectrophotometric method for lead determination by flow injection analysis with on-line preconcentration

A new flow injection (FI) system for the determination of Pb(II) at trace level with a preconcentration step and spectrophotometric detection is proposed. It is based on preconcentration of lead ions on chitosan and dithizone-lead complex formation in aqueous medium (pH 9). The chemicals and FIA variables influencing the performance of the system were optimized and applied to the determination of lead in natural, well, and drinking water samples. It is a simple, highly sensitive, and low cost alternative methodology. The method provided a linear rage between 25 and 250 μg l⁻¹, a detection limit of 5.0 ng ml⁻¹ and a sample throughput of 15 h⁻¹. The obtained results of spiked samples are in good agreement between the proposed method and ICP-AES.     

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 system for lead(II) determination in waste water by atomic absorption spectrometry using active carbon loaded with Pyrogallol Red.

An on-line system for enrichment and determination of lead(II) is presented. It is based on the adsorption of lead(II) ions on a minicolumn packed with active carbon loaded with Pyrogallol Red. After preconcentration step, the metal ions are eluted automatically by 5.0 ml of 0.50 M nitric acid solution and the lead ion contents were determined by atomic absorption spectrometry. The influence of chemicals, pH and flow variables were studied as well as effect of potential interfering ions. Under the optimum conditions, the lead ions in aqueous samples were concentrated about 100 fold by the column. The detection limit was 0.001 microg ml(-1). The recovery percent of spliced lead(II) was in the range of 98%-103%.     

Comparison of adsorbents for the preconcentration of sulfanilamides from aqueous solutions prior to HPLC determination

We studied the adsorption of sulfanilamide, sulfamethazine, sulfamethoxazole, sulfamethoxypyridazine, and sulfachloropyridazine on hypercrosslinked polystyrene, polymer adsorbents Strata-X and Strata SDB-L, carbon nanomaterial Taunit, and Diasorb-100-C₁₆T depending on the acidity of the solution and the concentration of adsorbates. Conditions were optimized for the preconcentration of sulfanilamides on a microcolumn packed with hypercrosslinked polystyrene. The compounds were desorbed with 1 mL of acetonitrile and determined in the eluate by reversed-phase HPLC with spectrophotometric detection at 255 nm. The preconcentration step decreases the detection limits for sulfanilamides by more than 60 times (to 3 ng/mL). The procedure was used for the analysis of a model mixture in river water.     

On-line preconcentration methods for capillary electrophoresis

The limits of detection (LOD) for capillary electrophoresis (CE) are constrained by the dimensions of the capillary. For example, the small volume of the capillary limits the total volume of sample that can be injected into the capillary. In addition, the reduced pathlength hinders common optical detection methods such as UV detection. Many different techniques have been developed to improve the LOD for CE. In general these techniques are designed to compress analyte bands within the capillary, thereby increasing the volume of sample that can be injected without loss of CE efficiency. This on-line sample preconcentration, generally referred to as stacking, is based on either the manipulation of differences in the electrophoretic mobility of analytes at the boundary of two buffers with differing resistivities or the partitioning of analytes into a stationary or pseudostationary phase. This article will discuss a number of different techniques, including field-amplified sample stacking, large-volume sample stacking, pH-mediated sample stacking, on-column isotachophoresis, chromatographic preconcentration, sample stacking for micellar electrokinetic chromatography, and sweeping.     

Flow-injection extraction spectrophotometric method for the determination of lead and its combination with minicolumn preconcentration

An automatic flow-injection method was developed for the determination of lead in the range 50–2000 μg l^?1. The method is based on the extraction of lead with the crown ether dicyclohexyl-18-crown-6 into chloroform from an acidic medium, subsequent addition of dithizone as chromogenic reagent to the extract and measurement of absorbance. The sample throughput is 45 h^?1. A microcolumn containing Chelex-100 chelating resin is used for on-line preconcentration of lead, giving a detection limit of 5 μg l^?1 with a sample throughout of 36 h^?1. The method compares favourably with the dithizone and diethyldithiocarbamate methods with respect to selectivity. Application to standard alloys, soil leachates and sea water is demonstrated.     

Factorial design in the optimization of preconcentration procedure for lead determination by FAAS

The present paper proposes a preconcentration procedure for lead determination using flame atomic absorption spectrometry (FAAS). It is based on lead(II) ions extraction as brilliant cresyl blue (BCB) complex and its sorption onto Diaion HP-2MG, a methacrylic ester copolymer. The optimization step was carried out using factorial design and the variables studied were pH, shaking time and reagent concentration. In the established experimental conditions, lead can be determinate with a limit of detection of 3.7 μg L⁻¹ lead (N = 20) and a relative standard deviation of 7% for a lead concentration of 100 μg L⁻¹. The accuracy was confirmed by analysis of a certified reference material, the stream sediment furnished by National Research Centre for Certified Reference Materials (NRCCRM), China (GBW 07310). Effect of other ions in the procedure proposed was also studied. The method was applied for lead determination in real samples of water, tea, soil and dust. Tests of addition/recovery in the experiments for lead determination in water samples revealed that the proposed procedure could be applied satisfactorily for analysis of these samples.     

Zirconium and hafnium determination by energy dispersive X-ray fluorescence with solid phase preconcentration

Two preconcentration methods has been developed for simultaneous determination of zirconium and hafnium by energy dispersive X-ray fluorescence (EDXRF). The first method is a liquid-solid extraction procedure with the use of an anionic exchange resin modified with xylenol orange. The second is a precipitation procedure carried out in the presence of lanthanum. Both methods permit significant enhancement of sensitivity in comparison with direct measurement in the aqueous phase. The applicability of both procedures for the preconcentration of Zr and Hf prior to their determination by EDXRF was demonstrated by analyzing synthetic mixtures and a sample of zirconium ore. The results obtained with the use of the modified resin show relative standard deviation of about 4% and good agreement with those obtained by spectrographic analysis.     

On-line spectrophotometric determination of scandium after preconcentration on XAD-4 resin impregnated with nalidixic acid

An on-line scandium preconcentration and determination method was developed with spectrophotometer associated with flow injection. Scandium from aqueous sample solution of pH 4.5 was selectively retained in the minicolumn containing XAD-4 resin impregnated with nalidixic acid at a flow rate of 11.8 mL min^?1 as scandium–nalidixic acid complex. The scandium complex was desorbed from the resin by 0.1 mol L^?1 HCl at a flow rate of 3.2 mL min^?1 and mixed with arsenazo-III solution (0.05 % solution in 0.1 mol L^?1 HCl, 3.2 mL min^?1) and taken to the flow through cell of spectrophotometer where its absorbance was measured at 640 nm. The preconcentration factors obtained were 35 and 155; detection limits of 1.4 and 0.32 μg L^?1 and sample throughputs of 40 and 11 were obtained for preconcentration time of 60 and 300 s, respectively. The tolerance limits of many interfering cations like Th(IV), U (VI), rare-earths and anions like tartrate, citrate, oxalate and fluoride were improved. The method was successfully applied to the determination of scandium from mock seawater samples and good recovery was obtained. The method was also validated on certified reference material IAEA-SL-1 (lake sediment) and the result was in good agreement with the reported value.     

On-line sorptive preconcentration platform incorporating a readily exchangeable Oasis HLB extraction micro-cartridge for trace cadmium and lead determination by flow injection-flame atomic absorption spectrometry

A simple, sensitive and inexpensive flow injection solid phase extraction (SPE) system was developed for automatic determination of trace level concentrations of metals. The potentials of this novel scheme, coupled to flame atomic absorption spectrometry (FAAS), were demonstrated for trace cadmium and lead determination in environmental water samples. The method was based on on-line chelate complex formation of target species with ammonium diethyldithiophosphate (DDTP), retention onto the surface of reversed-phase poly(divinylbenzene-N-vinylpyrrolidone) co-polymeric beads (Oasis HLB) and elution with methanol prior to atomization. A special PVC adapter was designed for easy and rapid replacement of the commercially available SPE cartridge. All main chemical and hydrodynamic parameters affecting the complex formation, sorption and elution of the analyte were optimized thoroughly. Moreover, the effect of potential interfering species occurring in environmental samples was also explored.For 90 s preconcentration time, enhancement factors of 155 and 180, detection limits (3s) of 0.09 μg L^− 1 and 0.9 μg L^− 1 and relative standard deviations (R.S.D.) of 2.9% (at 4.0 μg L^− 1) and 2.6% (at 20.0 μg L^− 1) were obtained for cadmium and lead, respectively, with a sample throughput of 24 h^− 1. The measurement trueness of the developed method was evaluated by analyzing a certified reference material and spiked environmental water samples. The proposed method is well suited to detect the target elements at concentration levels below the maximum allowed concentrations endorsed by the European Framework Directive (2008/105/EC) in inland and coastal waters.     

Spectrophotometric determination of trace lead in water after preconcentration using mercaptosephadex

A highly sensitive and selective spectrophotometric method for determination of trace lead in water after pre-concentration using mercaptosephadex (MS-50) has been developed, the method based on the color reaction of lead(II) with dibromohydroxylphenylporphyrin. Under optimal condition, lead(II) reacts with the reagent to form a 1:2 yellow complex in presence of TritonX-100, which has a maximum absorption peak at 479 nm. The color reaction can complete rapidly and remain stable for 24 h in room temperature. The molar absorption coefficient of the lead complex, the limit of quantification, the limit of detection and relative standard deviations were found to be 2.35×10⁵ l mol⁻¹ cm⁻¹, 4.3, 1.4 ng ml⁻¹ and 1.0%, respectively. The absorbance of the lead complex at 479 nm is linear up to 0.48 μg ml⁻¹ of lead(II). The effect of various co-existing ions in water were examined seriously. No interference was observed. Moreover, a simple pre-concentration method for trace lead in water was also studied using MS-50. It was found that trace lead in water can be adsorbed in 1.0 mol l⁻¹ HCl and dissociated from MS-50 with 4.0 mol l⁻¹ HCl quantitatively, that improves the selectivity and the sensitivity of method (its detection limit (3 s) changed into 0.2 ng ml⁻¹ of lead) obviously. The proposed method has been applied to determine trace lead in water samples with satisfactory results.     

On-line column preconcentration for the determination of cobalt in sea water by flow-injection chemiluminescence detection

A flow-injection method for the determination of dissolved cobalt(II) in sea water has been studied based on a combination of column preconcentration using 8-quinolinol immobilized on silica gel, fluoride containing metal alkoxide glass (8HQ-MAF) and chemiluminescence detection with a gallic acid-hydrogen peroxide system. Co(II) is selectively recovered from an acidified sample with 8-quinolinol immobilized on silica gel. After elution with dilute hydrochloric acid the resultant eluent is mixed with the reagent solutions, heated to 60^°C and then introduced into the CL cell. The analysis time including the 2-min sample load was 8 min per sea water sample with a corresponding detection limit of 0.62 ngl^-1 (3). The average standard deviation calculated for 10 replicate measurements of artificial sea water samples with a concentration of 10 ngl^-1 cobalt was ±2.1%. The method has been tested with the standard reference sea waters NASS and CASS.