Flow Injection On-line Preconcentration Research Articles

Flow Injection Solid Phase Extraction for Trace Metal Determination Using a Chelating Resin and Flame Atomic Absorption Spectrometry Detection

ABSTRACTThe development of a simple and sensitive on-line flow injection preconcentration system is reported using a polyamino-polycarboxylic acid chelating resin for the automated determination of cadmium(II), chromium(III), copper(II), and lead(II) in natural waters and urine by flame atomic absorption spectrometry (FAAS). The adsorbent showed a high sorption affinity for the metal ions at pH values from 5.0 to 6.0. The retained analytes were efficiently eluted by 1.5 mol/L HNO3. The effect of chemical and hydrodynamic parameters such as pH, selection of eluent (type, volume and concentration), and sample/eluent flow rates were studied, providing optimum conditions for the analysis of real samples. For a preconcentration time of 120 sec, the sampling frequency was 22/h and the enhancement factors were 105, 49, 106, and 98 for cadmium(II), chromium(III), copper(II), and lead(II), respectively. The detection limits were between 0.1 and 1.6 mg/L, while the precision was less than 3.3% as the relative standard deviation for all metal ions. The accuracy of the method was evaluated by the analysis of certified reference materials and fortified environmental and biological samples.

Flow-injection solid phase extraction using Dowex Optipore L493 loaded with dithizone for preconcentration of chromium species from industrial waters and determination by FAAS

An online flow injection preconcentration system for speciation of Cr(iii) and Cr(vi) based on the combination of solid phase extraction (SPE) and flame atomic absorption spectrometry (FAAS) has been described.

Flow Injection On-line Preconcentration of Trace Zinc(II) Ions in Water Samples Using a Synthesized 8-Hydroxyquinoline Functionalized Amberlite XAD-2 Resin and Determination by Flame Atomic Absorption Spectrometry

Flow Injection On-line Preconcentration of Trace Zinc(II) Ions in Water Samples Using a Synthesized 8-Hydroxyquinoline Functionalized Amberlite XAD-2 Resin and Determination by Flame Atomic Absorption Spectrometry

On-Line Flow Injection Preconcentration of Palladium in Environmental Waters Using a Microcolumn Packed with Silica Nanoparticles Modified by γ-Aminopropyltriethoxisilane and Determination by Flame Atomic Absorption Spectrometry

A novel solid phase sorbent with silica nanoparticles modified by γ-aminopropyltriethoxysilane (modified nanometer SiO2-γ-APS) was employed for the separation and preconcentration of palladium(II) before determination by flame atomic absorption spectrometry. The analytical conditions including pH, the eluent, and flow rates were optimized. Trace palladium(II) was quantitatively absorbed on a microcolumn of the sorbent at pH 5.0. The enrichment factor and sampling frequency were 45 and 12 h−1, respectively. Palladium(II) adsorbed on microcolumn was eluted quantitatively with 9% KSCN solution; the eluent solution was introduced into a flame atomic absorption spectrophotometer. The detection limit for palladium was 2.48 µ gL−1 and the relative standard deviation (RSD) was 1.8% (n = 11) at the 0.1 mg L−1 palladium level. The recoveries of palladium were 95.0% to 100.3%. The proposed method was successfully applied to the determination of palladium in pond and river water samples.

Determination of scandium in acid mine drainage by ICP-OES with flow injection on-line preconcentration using oxidized multiwalled carbon nanotubes

An on-line scandium preconcentration and determination system implemented with inductively coupled plasma optical emission spectrometry associated with flow injection was studied. Trace amounts of scandium were preconcentrated by sorption on a minicolumn packed with oxidized multiwalled carbon nanotubes, at pH 1.5. The retained analyte was removed from the minicolumn with 30% (v/v) nitric acid. A total enrichment factor of 225-fold was obtained within a preconcentration time of 300s (for a 25mL sample volume). The overall time required for preconcentration and elution of 25mL of sample was about 6min; the throughput was about 10 samples per hour. The value of the detection limit was 4ngL−1 and the precision for 10 replicate determinations at 100ngL−1 Sc level was 5% relative standard deviation, calculated from the peak heights obtained. The calibration graph using the preconcentration system was linear with a correlation coefficient of 0.9996 at levels near the detection limits up to at least 10mgL−1. After optimization, the method was successfully applied to the determination of Sc in an acid drainage from an abandoned mine located in the province of San Luis, Argentina.

Preconcentration and Determination of Trace Silver Ion Using Benzothiazole Calix[4]arene Modified Silica by Flow Injection Flame Atomic Absorption Spectrometry

The silica gel modified with benzothiazole calix[4]arene (APS-L1) via Schiff's base reaction was applied as a sorbent in an online system for preconcentration and determination of silver ion by flame atomic absorption spectrometry (FAAS). APS-L1 was used as an effective sorbent for solid phase extraction (SPE) of silver(I) ion in both batch and column methods. The optimum experimental parameters such as pH, eluent type, sample flow rate, eluent volume and eluent flow rate including the effect of interfering ions were investigated. Silver(I) ion was determined at pH 6-7. The capacity of APS-L1 sorbent was found to be 12.2 mg/g of sorbent. The high affinity was obtained without interference from the interfering ions. The optimum conditions of the online flow injection preconcentration coupled with the FAAS (FI-FAAS system) were evaluated. The sample flow rate was 3.0 mL min(-1) using sample volume of 5-10 mL. Elution was performed with 250 μL of 0.1 mol L(-1) thiosulfate at the flow rate of 1.5 mL min(-1). The analytical characteristics and performance of the FI-FAAS system were studied under optimum conditions using a solution spiked with standard silver(I) ion at 20 and 50 μg L(-1). The detection limit of 0.44 μg L(-1) was obtained. The accuracy of the proposed method was evaluated and percentages of recovery at 20 and 50 μg L(-1) were 100.2 and 99.5%, respectively. The percent relative standard deviations (%RSD) at 20 and 50 μg L(-1) were 6.1 and 3.3%, respectively. The developed method was successfully applied to determine trace silver(I) ion in drinking and tap water samples.

Calconcarboxylic acid dynamically modified nanometer-sized zirconia for on-line flow injection-inductively coupled plasma optical emission spectrometry determination of trace heavy metals in environmental water samples

A novel adsorbent was synthesized by grafting calconcarboxylic acid (CAA) dynamically to nanometer-sized zirconia (ZrO2) and was characterized with a transmission electron microscope, nitrogen adsorption instrument and infrared spectroscopy. By using CAA modified nanometer-sized ZrO2 as micro-column packing material, a new method of flow injection (FI) on-line preconcentration coupled with inductively coupled plasma optical emission spectrometry (ICP-OES) was developed for simultaneous determination of trace metals (Cd, Co, Cu, Ni and Pb) in environmental water samples. The experimental parameters including pH, sample flow rate and volume, elution volume and flow rate and coexisting ions on the extraction of the target analytes were investigated, and the optimal experimental conditions were established. Under the optimized operating conditions, the limits of detection (LODs) of this method for Cd, Co, Cu, Ni and Pb were 0.16, 0.04, 0.28, 0.22, and 0.95 ng mL−1, with the relative standard deviations (RSDs) of 2.2, 3.0, 4.5, 4.1 and 7.7% (n = 7, c = 10 ng mL−1), respectively. An enrichment factor of 10 and sampling frequency of 12 h−1 were obtained by using a loading time of 200 s and elution time of 30 s. The proposed method was validated by analysis of the target metals in Certified Reference Materials of GSBZ50009-88 environmental water and real-world natural water samples.

Spectrophotometric determination of phenol by flow injection on-line preconcentration with a micro-column containing magnetic microspheres functionalized with Cyanex272

A novel magnetic adsorbent, magnetic microsphere functionalized with Cyanex272, has been successfully synthesized via a chemical bonding alkylation method. A flow injection on-line preconcentration, with a micro-column packed with the as-synthesized magnetic adsorbent, coupled with UV-Vis spectrophotometric method was developed for the determination of phenol at a wavelength of 270 nm. Various experimental parameters were optimized as follows: eluent (methanol), sample flow rate (1.4 mL min−1), sample volume (1.4 mL), sample pH (5.0), and eluent flow rate (2.2 mL min−1). Under the optimum conditions, the intra-day and inter-day relative standard deviations were 1.37% and 2.69% (n = 5), respectively. The proposed method has been successfully applied to the determination of phenol in phenol ear drops, compound borax solution, and phenol ointment samples and the accuracy was assessed through recovery experiments.

FI-spectrophotometric determination of uranium after preconcentration on an anion exchange resin

An economical, fast, sensitive and selective method for the determination of uranium (VI) from sulfate media based on the flow injection on-line preconcentration in a minicolumn having amberlite IRA-402 (strong anion exchange) resin is described. Uranium (VI) was selectively adsorbed on the resin as uranyl trisulfate complex from aqueous solution of pH 2 in the minicolumn (2.56 mm i.d. and 7.5 cm in length) at a flow rate of 10 ml min−1. The adsorbed uranyl trisulfate complex was eluted by HClO4 (0.1 mol l−1, 6.5 ml min−1) and mixed with arsenazo-III (0.05 %, 6.5 ml min−1), and passed through the flow through cell of spectrophotometer where its absorbance was measured at 653 nm. Various parameters affecting adsorption and elution of the uranium complex were optimized. For data analyses peak absorbance was used. For 60 and 180 s preconcentration time, enrichment factors (EF) 20 and 40, sampling frequency (SF) 45 and 18 h−1; and detection limits (DL) (3σ) 14.2 and 8.6 μg l−1 were obtained, respectively. To enhance the sensitivity of the system, two minicolumns (described above) were used for simultaneous preconcentration and elution purpose. For 60 and 180 s preconcentration time, EF 30 and 50, SF 42 and 17 h−1 and DL (3σ) 4.4 and 3.44 μg l−1 were obtained, respectively. The effect of various anions and cations was studied for single column manifold. High selectivity of this method was observed. All the anions and cations studied did not interfere up to 330 times higher mass ratio to 300 μg l−1 U (VI) except Th(IV) which was tolerated up to 133 times by the addition of washing step in the manifold. The method based on single column manifold was applied on the spiked tap water, biological sample CRM (IAEA-V4) and synthetic leach liquor solution and good recovery was obtained. The method based on dual column manifold was validated on lake sediment SL-1 (CRM) and the results obtained were in good agreement at 95 % confidence level with the given value.

Flow injection dual-syringe sorbent extraction platform for metal determination in environmental matrices utilizing a new strong cation exchange sorbent micro-cartridge and flame atomic absorption spectrometry

A novel dual-syringe flow injection (DSFI) on-line column preconcentration system coupled to flame atomic absorption spectrometry (FAAS) has been developed for automatic trace metal determination in natural waters and biological samples. The proposed method was based on the on-line retention of Cd(II), Pb(II), Cu(II), Co(II) and Ni(II) ions onto the surface of a strong cation exchanger resin named HyperSepSCX, in a readily exchangeable micro-cartridge format and subsequent elution with HCl (2 mol L−1) prior to flame atomization. The sorbent and the micro-cartridge exhibited high long term chemical and mechanical stability with fast kinetics for all analytes. All main chemical and hydrodynamic factors affecting the performance of the proposed method were studied thoroughly. For 15.0 mL sample volume, the enhancement factors were calculated as 92, 97, 93, 99 and 77 for Cd(II), Pb(II), Cu(II), Co(II) and Ni(II) respectively and the detection limits (3 s) were in the range between 0.14 and 2.1 µg L−1. The precision (RSD) obtained was lower than 3.3% for all five metal ions with a sample throughput of 12 h−1. The developed method was evaluated by analyzing certified reference materials and spiked environmental natural water samples.

Unmodified Multi-Walled Carbon Nanotubes as Sorbent Material in Flow Injection on-Line Sorbent Extraction Preconcentration System for Cadmium Determination by Flame Atomic Absorption Spectrometry

Unmodified multi-walled carbon nanotubes (MWCNTs) were demonstrated as hydrophobic sorbent material for flow injection on-line microcolumn preconcentration coupled with flame atomic absorption spectrometry for cadmium determination in natural water samples. The method was based on on-line chelate complex formation between the analyte with sodium diethyldithiocarbamate and retention onto the surface of MWCNTs. Quantitative elution of the analyte was achieved with methanol which was whereupon delivered to the FAAS nebulizer for atomization and measurement. The microcolumn was packed with a mixture of MWCNTs and silica beads in order to minimize the generated back-pressure in the flow system which arises from the nano dimensions of MWCNTs. All factors affecting the performance of the proposed method were studied thoroughly. For a 180 s preconcentration time the enhancement factor was 54, the detection limit (3s) was 0.24 µg L−1, and the precision as relative standard deviation at a 5.0 µg L−1 Cd(II) concentration level was 3.2%. The method was applied to the analysis of environmental water samples and the accuracy evaluated via certified reference material and recovery experiments.

Flow injection on-line minicolumn preconcentration and determination of trace copper ions using an alumina/titanium oxide grafted silica matrix and FAAS

We describe the analytical performance of a hybrid material composed of SiO2, Al2O3 and TiO2. It was prepared by a sol–gel process and can act as an adsorbent in the continuous-flow enrichment of copper. A minicolumn was packed with the material, copper ions are adsorbed at pH 9.13, then eluted with 1.0 mol L−1 nitric acid, and determined by FAAS. The material was characterized by infrared spectroscopy, scanning electron and energy dispersive spectroscopy, energy dispersive X-ray fluorescence analysis, powder X-ray diffraction, and specific surface area analysis. No significant interference was observed for most ions in up to copper/interferent ratios of 1:100 and of 1:500 in case of Ca(II), Ba(II), and Mg(II). The breakthrough capacity is 1.4 mg g−1 under dynamic conditions. The limits of detection and of quantification are 0.50 and 1.4 μg L−1, respectively, and the calibration plot is linear in the range from 5.0 to 245.0 μg L−1 (r = 0.999). The relative standard deviation is 3.20 (for n = 7 and at a Cu(II) concentration of 10 μg L−1). The method was applied to the determination of trace copper ions in water, vegetable and alcohol fuel samples.

Improvement of copper FAAS determination conditions via preconcentration procedure with the use of salicylaldoxime complex trapped in polymer matrix

The paper presents application of a new resin dedicated to copper(II) flow-injection on-line preconcentration prior its flame atomic absorption spectrometric (FAAS) determination. The new sorbent, obtained by suspension polymerization technique, was styrene-divinylbenzene copolymer modified with 5-dodecylsalicylaldoxime-copper(II) complex. In flow mode leaching of initially imprinted Cu(II) ions from polymer beads was effective with 1% (v/v) nitric acid, however for elution of ions retained on the sorbent during the loading process sufficient efficiency was obtained for 0.5% (v/v) nitric acid. The most effective copper(II) sorption was observed within sample pH ca. 6.3 at flow rate 7.5mLmin−1. Furthermore, preconcentration studies of Cu(II) ions realized in the presence of popular foreign ions like Cd(II), Pb(II), Zn(II), Ni(II), Mn(II), Co(II) did not reveal significant interference. The expected effect of Cu(II)-imprinting was confirmed by higher tolerance level for interferents ions concentration for the new sorbent than for the control polymer. It was found that alkaline metals ions and humic acid had the most relevant influence on copper(II) uptake. Accuracy of the evaluated method was assessed for analysis of water samples (tap and mineral water, river water, artesian water) and certified water reference materials compare them to results obtained by inductively plasma mass spectrometry. The satisfactory relative error values obtained with use of standard addition calibration method, confirms the feasibility of this method for Cu(II) determination in water samples. Application of 120s sorption time enabled to obtain 74-fold enrichment factor and limit of detection (3σ) equal to 0.4μgL−1.

Determination of Four Kinds of Sulfonamides in Aquatic Products by Flow Injection On-line Preconcentration and High Performance Liquid Chromatography

Using activated carbon fibre as the absorbent,a flow injection on-line preconcentration-high performance liquld chromatographic method for the determination of four kinds of sulfonamides(sulfathiazole,sulfamethazine,sulfamonomethoxine and sulfaquinoxaline) in aquatic products was established.The samples were extracted by phosphate buffer solution,then preconcentrated on activated carbon fibre by flow injection.The separation was carried out with an Eclipse XDB-C18 column(250 mm×4.6 mm,5 μm) in the mobile phase system of formic acid solution-formic acid methanol solution(60 ∶ 40,V/V) at pH=3.0,the flow rate was 1.0 mL/min.The detection was performed at 270 nm wavelength.The experiment result showed that the good linear relationship was obtained in the sulfonamides concentrations from 0.001-0.064 mg/L with the correlation coefficient from 0.9997 to 0.9999.The detection limit was 0.48-1.15 μg/L(S/N=3).The enrichment factors for the four sulfonamides were from 137 to 406.The recoveries were 93.5%-104.0%.This method was easy to operate with precise result and good repetition and can be successfully applied to the determination of sulfathiazole,sulfamethazine,sulfamonomethoxine and sulfaquinoxaline.

Application of multiwall carbon nanotubes impregnated with 5-dodecylsalicylaldoxime for on-line copper preconcentration and determination in water samples by flame atomic absorption spectrometry

The paper presents application of multiwall carbon nanotubes (MWCNTs) modified with 5-dodecylsalicylaldoxime to copper(II) flow-injection on-line preconcentration and flame atomic absorption spectrometric (FAAS) determination. Two new sorbents were obtained by impregnation of MWCNTs with Cu(II)-LIX 622® complex, however in the first case modification was preceded by carbon wall activation via oxidization (Cu-LIX-CNT-A sorbent), and in the second one no surface activation was performed (Cu-LIX-CNT sorbent). It was found that effective leaching of initially introduced copper and Cu(II) retained in preconcentration process could be realized with the use 7% and 5% (v/v) nitric acid, for particular sorbents. Testing the influence of loading solution pH and rate of loading on sorption it was found out that optimal range of loading solution pH was about 4.5–6.3 for activated and 6.15–6.25 for non-activated CNT. Investigation of sorption kinetics showed that the process can be described by pseudo-second order reaction model. Sorption equilibrium conditions (90% sorption) for LIX-CNT-A and LIX-CNT were obtained after 8–15min, respectively and maximum sorption capacity for the new sorbents amounted to 18.1mgg−1 and 31.6mgg−1, respectively. For the examined sorbents enrichment factors increased with extension of loading time up to 180s: linearly for activated and non-linearly for non-activated MWCNTs. Influence of potential interferents such as Cd(II), Zn(II), Fe(III), Mg(II) and Ca(II) ions on copper(II) sorption on the new CNT materials was examined individually and with the use of 25–2 factorial design. The study revealed significant interference from iron, magnesium and calcium ions at relatively high concentrations. Applicability of the proposed sorbents was tested for Cu(II) determination in various kinds of water samples and the results were compared with those obtained with the use of ICP MS as a reference technique. Copper(II) determination in two certified reference materials: waste water (EU-H-3) and ground (ES-H-2) water was performed in order to assess trueness of the evaluated preconcentration procedures. Satisfactory values of relative errors were obtained for both procedures.

Salen impregnated silica gel as a new sorbent for on-line preconcentration of cadmium(II)

A new sorbent – salen impregnated silica gel – was prepared and characterised for application as a minicolumn packing for flow-injection on-line preconcentration of cadmium(II). The system was coupled with flame atomic absorption spectrometer (FI-FAAS). The optimal pH for Cd(II) sorption was in the range of 7.4–8.8 and nitric acid (1%, v/v) was efficient as eluent. Sorption was most effective within the sample flow rate up to 7 mL min−1. Sorption capacity of the sorbent found in a batch procedure was 26.3 µmol g−1 (2.95 mg g−1). Enrichment factor (EF) and limit of detection (LOD) obtained for 120-second loading time were 113 and 0.26 µg L−1, respectively. The sorbent stability in the working conditions was proved for at least 100 preconcentration cycles. The evaluated method was applied to Cd(II) determination in various water samples.

DETERMINATION OF TRACE CADMIUM BY FLOW INJECTION ON-LINE MICROCOLUMN PRECONCENTRATION COUPLED WITH FLAME ATOMIC ABSORPTION SPECTROMETRY USING HUMAN HAIR AS A SORBENT

A novel method using a cone-shaped pipette tip packed with human hair as an adsorption material has been developed for the on-line flow injection preconcentration of trace Cd(II) ions based on its complex formation with the ammonium pyrrolidine dithiocarbamate (APDC) prior to flame atomic absorption spectrometric (FAAS) determination. Cd-PDC complex sorbed on the human hair was eluted by 4.0 mol L−1 HNO3. The enhancement factor is 19, and the detection limit (3σ) is 0.77 μg L−1. The proposed method was successfully applied to the determination of trace cadmium in drinking water, beverage samples, and the certified reference materials.

Determination of trace metals in high-salinity petroleum produced formation water by inductively coupled plasma mass spectrometry following on-line analyte separation/preconcentration

A procedure is detailed for the determination of trace metals in high salinity petroleum produced formation water (PFW) by inductively coupled plasma mass spectrometry (ICP-MS) coupled with flow injection (FI) on-line matrix separation and preconcentration. High salinity PFW waters present complex composition containing various organic and inorganic substances. Mini-columns packed with Toyopearl AF-Chelate-650M iminodiacetate resin were used for the analyte separation/preconcentration of Cd, Pb, Ni, Zn, V, Co and U; Toyopearl 8-hydroxiquinoline resin for Fe, and silica immobilized 8-hydroxyquinoline resin for Mo. A Doehlert matrix and desirability function was used to generate response surfaces to optimize the column separation/preconcentration parameters. Using 7.5 mL aliquots of PFW, method limits of detection of 0.0007, 0.009, 0.017, 0.024, 0.0002, 0.047, 0.058, 0.002, 0.013 and 0.041 ng ml−1 were obtained for Cd, Pb, Ni, Zn, U, Mo, Fe, Co, V and Mn, respectively. Vanadium, Co and Mn were determined by the method of standard additions whereas Cd, Pb, Ni, Zn, Mo, Fe and U were quantitated using isotope dilution. CASS-4 (coastal seawater) certified reference material was used for method validation and high-salinity PFW (39–120‰) from Brazilian offshore platforms examined. The concentration ranges found in these waters were 0.013–1.47, 0.057–0.80, 0.229–5.1, 0.096–3360, 0.001–0.081, 0.244–69, 0.84–1419, 0.004–3.5, 0.088–0.85 and 4.2–6230 ng ml−1 for Cd, Pb, Ni, Zn, U, Mo, Fe, Co, V and Mn, respectively.

Preconcentración y atomización con tubo en la llama para la determinación de Cadmio en agua de mar

A flow injection on-line pre-concentration system coupled to thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) for cadmium determination at sub μg L-1 levels in seawater samples was developed. The on-line system was evaluated by analysing cadmium containing in a synthetic seawater matrix (2.5% m/v NaCl, 0.5% m/v MgCl2 and 0.8% m/v CaCl2). A sample volume of 2 mL allows determining Cd with a detection limits of 30 ng L-1 (3* σblank/slope), pre-concentration factor of 34 and repeatability of 1,8% (calculated as RSD, N=8 and containing 200 ng L-1 of Cd ).

Determination of Aniline Derivatives in Water Samples by High Performance Liquid Chromatography Coupled with On-Line Flow Injection Preconcentration

An on-line SPE-HPLC method using a cigarette filter as the sorbent was developed and applied to analyze the aniline derivatives in water samples. A preconcentration column packed with cigarette filters was used to replace a conventional sample loop on the injector valve of an HPLC for on-line SPE. With the consumption of a 7.5 mL sample solution, the enhancement factors ranged from 287 to 349 in comparison with direct injections of 20 μL sample solution. The detection limits (S/N = 3) for preconcentration of 7.5 mL of sample solution ranged from 0.27 to 5.46 μg/L at a sample throughput of 6 samples per hour.