Solid phase selective separation and preconcentration of Cu(II) by Cu(II)-imprinted polymethacrylic microbeads

Ion-imprinted polymer (IIP) particles are prepared by copolymerization of methacrylic acid as monomer, trimethylolpropane trimethacrylate as crosslinking agent and 2,2′-azo-bis-isobutyronitrile as initiator in the presence of Cu(II), a Cu(II)-4-(2-pyridylazo)resorcinol (Cu(II)-PAR) complex, and PAR only. A batch procedure is used for the determination of the characteristics of the Cu(II) solid phase extraction from the IIP produced. The results obtained show that the Cu(II)-PAR IIP has the greatest adsorption capacity (37.4 μmol g⁻¹ of dry copolymer) among the IIPs investigated. The optimal pH value for the quantitative preconcentration is 7, and full desorption is achieved by 1 M HNO₃. The selectivity coefficients (S_Cu/Me) for Me = Ni(II), Co(II) are 45.0 and 38.5, respectively. It is established that Cu(II)-PAR IIPs can be used repeatedly without a considerable adsorption capacity loss. The determination of Cu(II) ions in seawater shows that the interfering matrix does not influence the preconcentration and selectivity values of the Cu(II)-PAR IIPs. The detection and quantification limits are 0.001 μmol L⁻¹ (3σ) and 0.003 μmol L⁻¹ (6σ), respectively.     

A new room temperature ionic liquid 1-butyl-3-trimethylsilylimidazolium hexafluorophosphate as a solvent for extraction and preconcentration of mercury with determination by cold vapor atomic absorption spectrometry

A new room temperature ionic liquid 1-butyl-3-trimethylsilylimidazolium hexafluorophosphate abbreviated as [C₄tmsim][PF₆] was synthesized and developed as a novel medium for liquid/liquid extraction of inorganic mercury in this work. Under optimal condition, o-carboxyphenyldiazoamino-p-azobenzene abbreviated as CDAA reacted with inorganic mercury to form a neutral Hg-CDAA complex, the complex was rapidly extracted into ionic liquid phase. After back-extracting into aqueous phase with sulfide sodium solution, the mercury concentration was detected by cold vapor atomic absorption spectrometry. The extraction and back-extraction efficiencies were 99.9 and 100.1% for 5.0 μg L⁻¹ standard mercury in 1000 mL of water solution, respectively. The detection limit, calculated using three times the standard error of estimate of the calibration graph, is 0.01 ng of mercury per milliliter water sample. The proposed method has been used to the determination of trace inorganic mercury in natural water with satisfactory results. Moreover, Zeta potential and surface tension of [C₄tmsim][PF₆] solution were measured and applied to explain the extraction mechanism of [C₄tmsim][PF₆] system.     

Preconcentration of copper on ion-selective imprinted polymer microbeads

Molecular recognition-based separation techniques have received much attention in various fields because of their high selectivity for target molecules. Molecular imprinting has been recognized as a promising technique for the preparation of such systems. In this study, we have prepared a novel molecular imprinted adsorbent to remove heavy metal ions with high selectivity. The Cu(II)-imprinted poly(ethylene glycol dimethacrylate–methacryloylamidohistidine/Cu(II)) (poly(EGDMA–MAH/Cu(II))) microbeads with an average size of 150–200 μm were prepared by dispersion polymerization. These Cu(II) imprinted microbeads were used in the adsorption–desorption of copper(II) ions from metal solutions. Adsorption equilibria was achieved in about 1 h. The maximum adsorption of Cu(II) ions onto imprinted microbeads was about 48 mg/g. The pH significantly affected the adsorption capacity of imprinted microbeads. The observed adsorption order under competitive conditions was Cu(II) > Zn(II) > Ni(II) > Co(II) in mass basis. The imprinted microbeads can be easily regenerated by 0.1 M EDTA solution with higher effectiveness. The imprinted microbeads showed excellent selectivity for the target molecule (i.e. Cu(II) ions due to molecular geometry). These features make imprinted microbeads very good candidate for selective removal of Cu(II) ions at high adsorption capacity. Detection limit was increased at least 1000-folds with the preconcentration approach using the imprinted microbeads. The method was also applied to certified reference and seawater samples.     

Speciation analysis of mercury in water samples by cold vapor atomic absorption spectrometry after preconcentration with dithizone immobilized on microcrystalline naphthalene

Trace amounts of inorganic mercury (Hg²⁺) and methylmercury cations (MeHg²⁺) were adsorbed quantitatively from acidic aqueous solution onto a column packed with immobilized dithizone on microcrystalline naphthalene. The trapped mercury was eluted with 10 ml of 7 mol L^–1 hydrochloric acid solution. The Hg²⁺ was then directly reduced with tin (II) chloride, and volatilized mercury was determined by cold vapor atomic absorption spectrometry (CVAAS). Total mercury (Hgt) was determined after decomposition of MeHg⁺ into Hg²⁺. Hg²⁺ and MeHg⁺ cations were completely recovered from the water with a preconcentration factor of 200. The relative standard deviation obtained for eight replicate determinations at a concentration of 0.3 g L^–1 was 1.8%. The procedure was applied to analysis of water samples, and the accuracy was assessed via recovery experiment.     

Assessment of ion imprinted polymers based on Pd(II) chelate complexes for preconcentration and FAAS determination of palladium

New ion-imprinted polymeric (IIP) materials were synthesized by copolymerization of 4-vinylpyridine (VP) and styrene as functional monomers and divinylbenzene as a cross-linking agent with chelating complexes of Pd(II) in the presence of 2,2-azobisisobutyronitrile as an initiator. The complexes of Pd(II) with ammonium pyrrolidinedithiocarbamate (APDC), N,N′-diethylthiourea (DET), and dimethylglyoxime (DMG) were used for this purpose. Chloroform, ethanol, and cyclohexanol were applied as porogens. The ion-imprinted polymers were tested in a flow mode as sorbents for solid-phase extraction of palladium from aqueous solutions. The conditions of Pd(II) separation on all polymers were optimized. The efficiencies of retention of Pd on different polymers in the presence of high excess of interfering ions were compared. The effect of the used porogen on the analytical performance of the prepared polymers was also investigated. The calculated sorbent capacities for Pd(II) were in the range from 9.25 mg g⁻¹ to 13.3 mg g⁻¹. The sorbent with Pd(II) imprinted as Pd-DMG-VP complex in chloroform was used for preconcentration of trace amounts of Pd. The detection limit for 100 mL of the sample was 5 μg L⁻¹ using flame atomic absorption spectrometry (FAAS). The developed method was applied for the determination of Pd in water samples.     

Sequential quantification of methyl mercury in biological materials by selective reduction in the presence of mercury(II), using two gas–liquid separators

The present procedure is based on the sequential selective reduction of mercury(II) and methyl mercury using two gas–liquid separators in series. Cold vapor atomic absorption spectrometry was used for detection. Mercury(II) is reduced by a 0.01% m/v sodium tetrahydroborate solution and driven to the absorption cell in the first separator. The methyl mercury species is reduced by the same reductant but at a 0.3% m/v concentration, and in the presence of iron(III) chloride. Parameters such as argon flow rate, and the NaBH₄ and dithiophosphoric acid diacyl ester concentrations were optimized. At the optimized conditions, and using aqueous standards for calibration, the corresponding limits of detection (3σ_b, n=10) were 400 and 600 ng l⁻¹ for mercury(II) and methyl mercury, respectively. The sample throughput was 12 h⁻¹. The procedure was used for the determination of methyl mercury in dogfish liver and dogfish muscle certified reference materials, and good concordance between found and certified values was observed.     

Silk fibroin as a sorbent for on-line extraction and preconcentration of copper with detection by electrothermal atomic absorption spectrometry

Silk fibroin is a kind of polypeptide with functional amino acids in its structure. The electric charges in its molecular chains originating from the dissociation of acidic groups, i.e., hydroxyl, phenol and carboxyl, provide vast potentials for the retention of metal species of interest. In this study, the selective retention of Cu²⁺ with silk fibroin at pH 6.0 was investigated and a novel on-line procedure for separation/preconcentration of Cu²⁺ from complex sample matrices was thus developed by using a sequential injection system with an electrothermal atomic absorption spectrometry. A novel concept of enrichment index (EI), i.e., defined as enrichment factor (EF) obtained by consuming unity of sample volume (ml), was proposed for evaluating the enrichment efficiency of a flow-based preconcentration procedure. With a sampling volume of 900 μl, an EI of 30.3 (EF = 27.3) was achieved, which was much improved as compared to that of reported procedures. A detection limit of 8.0 ng l⁻¹ was achieved within a linear range of 0.025-1.5 μg l⁻¹ along with a precision of 2.2% R.S.D. at 0.5 μg l⁻¹. The practical applicability of this procedure was validated by analyzing a certified reference material of riverine water (GBW08608) and a certified reference material of seawater (NASS-5) achieving satisfactory agreements between the certified and the obtained values. A spiking recovery was also performed by using a cave water sample.     

Spherical silica particles decorated with graphene oxide nanosheets as a new sorbent in inorganic trace analysis

Graphene oxide (GO) is a novel material with excellent adsorptive properties. However, the very small particles of GO can cause serious problems is solid-phase extraction (SPE) such as the high pressure in SPE system and the adsorbent loss through pores of frit. These problems can be overcome by covalently binding GO nanosheets to a support. In this paper, GO was covalently bonded to spherical silica by coupling the amino groups of spherical aminosilica and the carboxyl groups of GO (GO@SiO₂). The successful immobilization of GO nanosheets on the aminosilica was confirmed by scanning electron microscopy and X-ray photoelectron spectroscopy. The spherical particle covered by GO with crumpled silk wave-like carbon sheets are an ideal sorbent for SPE of metal ions. The wrinkled structure of the coating results in large surface area and a high extractive capacity. The adsorption bath experiment shows that Cu(II) and Pb(II) can be quantitatively adsorbed at pH 5.5 with maximum adsorption capacity of 6.0 and 13.6 mg g⁻¹, respectively. Such features of GO nanosheets as softness and flexibility allow achieving excellent contact with analyzed solution in flow-rate conditions. In consequence, the metal ions can be quantitatively preconcentrated from high volume of aqueous samples with excellent flow-rate. SPE column is very stable and several adsorption–elution cycles can be performed without any loss of adsorptive properties. The GO@SiO₂ was used for analysis of various water samples by flame atomic absorption spectrometry with excellent enrichment factors (200–250) and detection limits (0.084 and 0.27 ng mL⁻¹ for Cu(II) and Pb(II), respectively).     

Synthesis and application of a nanoporous ion‐imprinted polymer for the separation and preconcentration of trace amounts of vanadium from food samples before determination by electrothermal atomic absorption spectrometry

A vanadium ion‐imprinted polymer was synthesized in the presence of V(V) and N‐benzoyl‐N‐phenyl hydroxyl amine using 4‐vinyl pyridine as the monomer, ethylene glycol dimethacrylate as the cross linker and 2,2’‐azobis(isobutyronitrile) as the initiator. The imprinted V(V) ions were completely removed by leaching the polymer with 5 mol/L nitric acid, and the polymer structure was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The ion‐imprinted polymer was used as the sorbent in the development of the solid‐phase extraction method for V(V) prior to its determination by electrothermal atomic absorption spectrometry. The maximum sorption capacity for V(V) ions was 26.7 mg/g at pH 4.0. Under the optimum conditions, for a sample volume of 150.0 mL, an enrichment factor of 289.0 and a detection limit of 6.4 ng/L were obtained. The developed method was successfully applied to the determination of vanadium in parsley, zucchini, black tea, rice, and water samples.     

Rapid determination of total mercury in treated waste water by cold vapor atomic absorption spectrometry in alkaline medium with sodium hypochlorite solution

Addition of a sodium hypochlorite solution (9.2% (w/v)) was effective to reduce a sulfide interference in determination of organic mercury, including methylmercury and phenylmercury, as well as a previously reported determination of inorganic mercury by cold vapor atomic absorption spectrometry (CVAAS) in an alkaline medium. Total mercury ranging from 0.17 to 33 μg L⁻¹ in 15 mL of sample solutions containing up to 200 mg L⁻¹ of sulfide can be determined without any serious interference by sulfide when 1 mL of the sodium hypochlorite solution was added after dilution of the sample solution to 25 mL. The proposed method was simple and rapid because no digestion processes were required for the determination of total mercury; the time required for the determination was only about 5 min. The proposed method was applicable to the analysis of treated waste water.     

用间接法测定硫化物的研究

前人已经报道用汞的冷原子吸收法测定硫化物,利用Hg~(2+)和S~(2-)形成很稳定的化合物,使汞的吸光度值降低,根据其降低的程度来测定硫化物的含量。这种方法简便、灵敏,但对加入的Hg~(2+)量有较大的限制。S_2O_3~(2-)、CN~-、I~-等也有严重干扰,这些离子常与S~(2-)共存于水样中,所以,实际测定时,常需分离这些离子。     

A novel preconcentration method for determination of iron and lead using Chromosorb-103 and flame atomic absorption spectrometry

Syringe connected-minicolumn (SCM) method for the preconcentration/separation of iron and lead prior to their determination by flame atomic absorption spectrometry (FAAS) was developed. The proposed method is substituted for classical batch and column methods. The method proposed was compared with the column method with respect to easiness, rapidness, simplicity and some analytical performance criteria such as recovery, precision, accuracy and risk of contamination. A minicolumn was filled with Chromosorb-103 as a sorbent and connected with a syringe. The experimental conditions such as pH of sample, concentration and amount of eluent, flow rates of sample and eluent, concentration of 8-hydroxyquinoline (oxine) as a complexing agent were optimized. The sample solution with or without oxine was drawn into the syringe and discharged manually passing through the resin. Analytes were retained at pH ≥5 and eluted with 1 M nitric acid in acetone quantitatively. Analyte elements could be concentrated up to 200-fold. The iron and lead in river-water samples and in certified reference Bovine Liver (NIST 1577b) were quantitatively recovered with relative standard deviation lower than 10%.     

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.     

Evaluation of high pressure oxygen microwave-assisted wet decomposition for the determination of mercury by CVAAS utilizing UV-induced reduction

The UV-induced cold vapor generation with formic acid coupled to AAS after high pressure oxygen microwave decomposition was developed for determination of total Hg in analytical samples. Certified reference materials were decomposed in 1.5 mol L^{− 1} HNO₃ and 0.6 mol L^{− 1} H₂O₂. Microwave decomposition with oxygen has allowed the use of diluted reagents. The oxygen at a pressure of ca. 15 bar was delivered during the mineralization to the closed vessel. Interference by unused residues of H₂O₂ and HNO₃ was observed. In order to overcome the negative effect of remaining oxidants pre-reduction with hydroxylammonium chloride at a concentration 0.75 mmol L^{− 1} was used. Recovery of mercury in four reference materials containing 0.20–1.99 µg g^{− 1} Hg were 99–104% of certificate values. The limits of detection and quantification in the sample solutions were determined as 0.12 and 0.38 µg L^{− 1}, which corresponds to absolute detection limits of 12 and 38 ng g^{− 1} for total mercury, respectively. The results were in good agreement with the t-test at a 95% confidence level of the certified values in the investigated reference materials. The relative standard deviation was better than 7% for most of the samples.     

Ultratrace determination of cadmium by cold vapor atomic absorption spectrometry after preconcentration with a simplified cloud point extraction methodology

A simplified micelle-mediated extraction methodology for the preconcentration of ultratrace levels of cadmium as a prior step to its determination by cold vapor atomic absorption spectrometry (CV-AAS) has been developed. The methodology is based on the cloud point extraction (CPE) of cadmium at pH 8 by using the non-ionic surfactant polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5) without adding any chelating agent. Cadmium cold vapor was generated from 2 ml of the extracted surfactant-rich phase by means of sodium tetrahydroborate (3%, w/v) as a reducing agent and hydrochloric acid (0.2 mol l⁻¹) as a carrier solution. Several important variables that affect the cloud point extraction and cold vapor cadmium generation efficiency were investigated and optimized. The preconcentration of only 50 ml of solution in the presence of 0.06% (v/v) PONPE 7.5 gives an enhancement factor of 62. The calibration graph using the preconcentration system was linear in the range of 4-100 ng l⁻¹ with a correlation coefficient of 0.9992. Detection limit (3 s) obtained in the optimal conditions was 0.56 ng l⁻¹. The relative standard deviation (R.S.D.) for six replicate determinations at 20 ng l⁻¹ Cd level was 3.2%. The proposed method was successfully applied to the ultratrace determination of cadmium in water samples.     

Fullerenes as sorbent materials for benzene, toluene, ethylbenzene, and xylene isomers preconcentration

A simple and novel SPE system for benzene, toluene, ethylbenzene, and xylene isomers (BTEX) compounds in water is proposed in which samples are directly propelled from a 15 mL glass vial through a sorbent column by means of a needle, thereby avoiding evaporative losses and the sorption of BTEX on the manifold materials. Following elution with 150 microL of ethyl acetate, 1 microL of extract is injected into a gas chromatograph-mass spectrometer system. A comparative study of various sorbent materials (C60 fullerene, Tenax TA, and RP-C18) revealed C60 fullerene to be the best choice in terms of sensitivity (a likely result of its increased sample breakthrough volume), precision (the surfactant medium used to prepare samples minimizes evaporative losses), selectivity (C60 fullerene only interacts with nonpolar aromatic compounds), and reusability (columns containing 60 mg of C60 fullerene remain serviceable for at least 6 months). This C60 fullerene-based method exhibits a linear range of 0.1-100 microg/L, a detection limit of 0.04 microg/L, and an RSD of ca. 3%. It was applied to the determination of BTEX in various types of water including sea and waste water with good precision.     

Ti(IV) ion-imprinted polymer as a new selective sorbent for extraction and pre-concentration of trace amounts of titanium ions in different samples

ABSTRACT

In this paper, a novel, simple, selective and effective solid phase extraction method based on ion-imprinted polymer (IIP) technology and flame atomic absorption spectrometry (FAAS) for separation and pre-concentration of trace amounts of titanium (IV) ions was reportd?. It was obtained by precipitation polymerisation by using 2-(2,4-dihydroxyphenyl)-3,5,7-trihydroxychromen-4-one titanium (IV) complex abbrivated as Ti(IV)-(morin), as the template molecule. After polymerisation, leaching the polymer in HNO₃ (50% (v/v) solution caused formation cavities in the polymer. Characterisation studies of the ?Ti(IV)-imprinted polymer (Ti-IP) was performed by FT-IR, UV-Vis and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS) techniques and then, the effective factors on extraction were optimised. A sensitive response to Ti(IV) within a concentration range between 0.01 and 4.0 μg mL^?1 was achieved under the optimum conditions. A total of 10.0 ng mL^?1 and 80.0 mg g^?1 were obtained as limit of detection (LOD, 3Sb/m) and maximum adsorption capacity, respectively. The relative standard deviation (RSD) for eight replicates detections of 0.2 μg mL^?1 of Ti(IV)? was found to be 2.8%. By this method, pre-concentration factor (PF) of 100 was obtained. Successfully applying this method in the water and standard samples, reasonable results were obtained for the extraction and pre-concentration of the titanium ions.     

Mercury species immobilized on sulphydryl cotton: A new candidate reference material for mercury speciation

A batch of sulphydryl cotton microcolumns was prepared and charged with a mixed Hg standard solution (methyl-, ethyl- and inorganic Hg, 10 g l^–1 as Hg, 3 ml) and stored at 4 °C in a light-tight box. At regular time intervals over a 4 month period microcolumns were removed and Hg species were quantified by gas chromatography microwave-induced plasma atomic emission spectrometry (after elution, extraction and derivatization steps). It was found that analyte recoveries for methyl- and inorganic Hg were quantitative over the 4 month period while ethyl-Hg species appeared to be stable for up to 2 months.     

Modified mesoporous silica materials for on-line separation and preconcentration of hexavalent chromium using a microcolumn coupled with flame atomic absorption spectrometry

A modified SBA-15 mesoporous silica material NH₂-SBA-15 was synthesized successfully by grafting γ-aminopropyl-triethoxysilane. The material was characterized using transmission electron microscopy (TEM) and Fourier transform infrared/Raman (FT-IR/Raman) spectroscopy, and used for the first time in a flow injection on-line solid phase extraction (SPE) coupled with flame atomic absorption spectrometry (FAAS) to detect trace Cr (VI). Effective sorption of Cr (VI) was achieved at pH 2.0 with no interference from Cr (III) and other ions and 0.5 mol L⁻¹ NH₃·H₂O solution was found optimal for the complete elution of Cr (VI). An enrichment factor of 44 and was achieved under optimized experimental conditions at a sample loading of 2.0 mL min⁻¹ sample loading (300 s) and an elution flow rate of 2.0 mL min⁻¹ (24 s). The precision of the 11 replicate Cr (VI) measurements was 2.1% at the 100 μg L⁻¹ level with a detection limit of 0.2 μg L⁻¹ (3 s, n = 10) using the FAAS. The developed method was successfully applied to trace chromium determination in waste water. The accuracy was validated using a certified reference material of riverine water (GBW08607).