Removal of heavy metal ions from aqueous solutions by filtration with a novel complexing membrane containing poly(ethyleneimine) in a poly(vinyl alcohol) matrix

A novel complexing membrane was used for the removal of heavy metal ions such as Pb(II), Cd(II) and Cu(II) from aqueous solutions. The membrane consists in a semi-interpenetrating polymer network of crosslinked poly(vinyl alcohol) as the matrix and poly(ethyleneimine) as the complexing polymer. The absorption reactions followed pseudo-first-order kinetics with similar rate constants for the three cations. A model is proposed for the absorption–desorption process in order to rationalize the data obtained for the retention ratio and the retention efficiency ratio. The corresponding equilibrium constants were determined for the three metal ions, showing that the affinity order of the membrane is Pb > Cu > Cd. This sequence is consistent with the order of maximum uptake of the ions per gram of membrane: 0.59, 0.47 and 0.33 mmol g⁻¹, respectively. On the other hand, the uptake order is different on a mass basis: 123, 30 and 37 mg g⁻¹, respectively. Regeneration of the membrane and metal recovery were studied with HCl and HNO₃ at different concentrations. Filtration of solutions of each metal ion showed large elimination ratios (96–99.5%) with a retention sequence Cd > Cu > Pb. The membrane remained efficient until complete saturation of its sites. Moreover, Cu retention is larger than expected, indicating possible additional chelation by the PVA matrix. Better retention ratios were observed when the concentration of the feed solution was kept constant. Filtration of a mixture of the three cations (all at 100 ppm concentration) resulted in the same retention sequence, but the elimination ratios were smaller and Pb was eventually displaced by Cu and Cd that were present in larger molar concentrations.     

Determination of trace impurities in boron nitride by graphite furnace atomic absorption spectrometry and electrothermal vaporization inductively coupled plasma optical emission spectrometry using solid sampling

Two digestion-free methods for trace analysis of boron nitride based on graphite furnace atomic absorption spectrometry (GFAAS) and electrothermal vaporization inductively coupled plasma spectrometry optical emission (ETV-ICP-OES) using direct solid sampling have been developed and applied to the determination of Al, Ca, Cr, Cu, Fe, Mg, Mn, Si, Ti and Zr in four boron nitride materials in concentration intervals of 1–23, 54–735, 0.05–21, 0.005–1.3, 1.6–112, 4.5–20, 0.03–1.8, 6–46, 38–170 and 0.4–2.3 μg g^− 1, respectively. At optimized experimental conditions, with both methods, effective in-situ analyte/matrix separation was achieved and calibration could be performed using calibration curves measured with aqueous standard solutions. In solid sampling GFAAS, before sampling, the platform was covered with graphite powder and, for determination of Si, also the Pd/Mg(NO₃)₂ modifier was used. In the determination of all analyte elements by solid sampling ETV-ICP-OES, Freon R12 was added to argon carrier gas. For solid sampling GFAAS and ETV-ICP-OES, the achievable limits of detection were within 5 (Cu)–130 (Si) ng g^− 1 and 8 (Cu)–200 (Si) ng g^− 1, respectively. The results obtained by these two methods for four boron nitride materials of different purity grades are compared each with the other and with those obtained in analysis of digests by ICP-OES. The performance of the two solid sampling methods is compared and discussed.     

Mass Spectrometric Observation of Doubly Charged Alkaline‐Earth Argon Ions

Doubly charged diatomic ions MAr²⁺ where M=Mg, Ca, Sr or Ba have been observed by mass spectrometry with an inductively coupled plasma ion source. Abundance ratios are quite high, 0.1 % for MgAr²⁺, 0.4 % for CaAr²⁺, 0.2 % for SrAr²⁺ and 0.1 % for BaAr²⁺ relative to the corresponding doubly charged atomic ions M²⁺. It is assumed that these molecular ions are formed through reactions of the doubly charged metal ions with neutral argon atoms within the ion source. Bond dissociation energies (D₀) were calculated and agree well with previously published values. The abundance ratios MAr⁺/M⁺ and MAr²⁺/M²⁺ generally follow the predicted bond dissociation energies with the exception of MgAr²⁺. Mg²⁺ should form the strongest bond with Ar [D₀ (MgAr²⁺)=124 to 130 kJ mol^?1] but its relative abundance is similar to that of the weakest bound BaAr²⁺ (D₀=34 to 42 kJ mol^?1). The relative abundances of the various MAr²⁺ ions are higher than those expected from an argon plasma at T=6000 K, indicating that collisions during ion extraction reduce the abundance of the MAr²⁺ ions relative to the composition in the source. The corresponding singly charged MAr⁺ ions are also observed but occur at about three orders of magnitude lower intensity than MAr²⁺.     

Evaluation of liquid chromatography inductively coupled plasma mass spectrometry for arsenic speciation in water from industrial treatment of shale

This work describes an arsenic speciation analysis in aqueous effluent from a shale industrial plant using liquid chromatography coupled to inductively coupled plasma mass spectrometry (LC–ICP–MS). Arsenic species have been separated through an anion-exchange column and several parameters investigated, such as retention time, pH, flow rate and concentration of the mobile phase (ammonium carbonate), chloride interference and column conditioning time. The best conditions have been found by fixing the pH of the mobile phase at 8.7. Keeping the mobile phase flow rate at 1.5 ml min^− 1, arsenic species were separated by varying the concentration of the mobile phase and the time of elution, as follow: 1.5 mmol l^− 1 for 10 min, 12 mmol l^− 1 for 10 min and 20 mmol l^− 1 for 10 min, respectively. Up to 13 As species present in the samples were separated under these conditions and the following species could be identified and quantified: arsenite [As(III)], dimethylarsinic acid (DMA), monomethylarsonic acid (MMA) and arsenate [As(V)]. The limits of detection of the LC–ICP–MS method were 0.02, 0.06, 0.04 and 0.10 μg l^− 1 of As(III), DMA, MMA, and As(V), respectively. The concentration of these species in the samples were from 3.7 to 6.4 μg l^− 1, 6.9 to 13.2 μg l^− 1, 100 to 142 μg l^− 1 and 808 to 1363 μg l^− 1 for As(III), DMA, MMA and As(V), respectively. The accuracy, evaluated by recovery tests, varied from 94 to 105% and the precision, evaluated by the relative standard deviation was typically lower than 10%.     

Accurate determination of ultra-trace levels of Ti in blood serum using ICP-MS/MS

Ti is frequently used in implants and prostheses and it has been shown before that the presence of these in the human body can lead to elevated Ti concentrations in body fluids such as serum and urine. As identification of the exact mechanisms responsible for this increase in Ti concentrations, and the risks associated with it, are not fully understood, it is important to have sound analytical methods that enable straightforward quantification of Ti levels in body fluids (for both implanted and non-implanted individuals). Until now, only double-focusing sector field ICP-mass spectrometry (SF-ICP-MS) offered limits of detection that are good enough to deal with the very low basal levels of Ti in human serum. This work reports on the development of a novel method for the accurate and precise determination of trace levels of Ti in human serum samples, based on the use of ICP-MS/MS. O₂ and NH₃/He have been compared as reaction gases. While the use of O₂ did not enable to overcome all spectral interferences, it has been shown that conversion of Ti⁺ ions into Ti(NH₃)₆⁺ cluster ions by using NH₃/He as a reaction gas in an ICP-QQQ-MS system, operated in MS/MS mode, provided interference-free conditions and sufficiently low limits of detection, down to 3 ng L⁻¹ (instrumental detection limit obtained for the most abundant Ti isotope). The accuracy of the method proposed was evaluated by analysis of a Seronorm Trace Elements Serum L-1 reference material and by comparing the results obtained with those achieved by means of SF-ICP-MS. As a proof-of-concept, the newly developed method was successfully applied to the determination of Ti in serum samples obtained from individuals with and without Ti-based implants. All results were found to be in good agreement with those obtained by means of SF-ICP-MS. The typical basal Ti level in human serum was found to be <1 μg L⁻¹, while values in the range of 2–6 μg L⁻¹ were observed for implanted patients.     

1-(2-Formamidoethyl)-3-phenylurea functionalized activated carbon for selective solid-phase extraction and preconcentration of metal ions

A novel method that utilizes 1-(2-formamidoethyl)-3-phenylurea-modified activated carbon (AC-1-(2-formamidoethyl)-3-phenylurea) as a solid-phase extractant has been developed for simultaneous preconcentration of trace Cr(III), Cu(II), Fe(III) and Pb(II) prior to the measurement by inductively coupled plasma atomic emission spectrometry (ICP-AES). Experimental conditions for effective adsorption of trace levels of Cr(III), Cu(II), Fe(III) and Pb(II) were optimized using batch and column procedures in detail. The optimum pH value for the separation of metal ions simultaneously on the new sorbent was 4. And the adsorbed metal ions could be completely eluted by using 2.0 mL 2.0 mol L⁻¹ HCl solution. Common coexisting ions did not interfere with the separation and determination of target metal ions. The maximum static adsorption capacity of the sorbent at optimum conditions was found to be 39.8, 39.9, 77.8 and 17.3 mg g⁻¹ for Cr(III), Cu(II), Fe(III) and Pb(II), respectively. The detection limits of the method were found to be 0.15, 0.41, 0.27 and 0.36 ng mL⁻¹ for Cr(III), Cu(II), Fe(III) and Pb(II), respectively. The relative standard deviation (RSD) of the method was lower than 4.0% (n = 8). The method was successfully applied for the preconcentration of trace Cr(III), Cu(II), Fe(III) and Pb(II) in natural and certified samples with satisfactory results.     

Determination of Rare Earth Elements in Garnet Minerals,Geological Materials by Inductively Coupled Plasma–Atomic Emission Spectral and Mass Spectral Analysis

Abstract

The performance of inductively coupled plasma–atomic emission spectrometry (ICP‐AES) for the determination of 14 lanthanides and Yttrium was evaluated by comparison with inductively coupled plasma–mass spectral (ICP‐MS) analysis. The geochemical reference samples (GRS), DNC‐1(diabase), AGV‐1(andesite), Sy‐2(syenite), MRG‐1(gabbro), AN‐G(anorthosite), AC‐E(granite), and MAG‐1(marine mud) were chosen as test materials and analyzed for checking the precision and reproducibility of the methods. The mineral garnet is separated from the black sands of the southwest coast of India, and the combined cation exchange–ICP method of AES analysis and MS analysis were carried out for the determination of rare earth elements. Both techniques are within the requirements needed for garnet minerals. The determination of rare‐earth elements in these minerals, which contain other elements as major contribution and trace distribution of rare‐earth elements, shows that ICP applied under the proper working condition lives up to the expectations. Major element analysis gives the formula of garnet of Manavalakurichi (MK) as (FeCaMg)_2.79Al_2.07Si_3.05O₁₂ approximated to Fe₃Al₂Si₃O₁₂, hence of almandine-type garnet. The enrichment of heavy lanthanides compared to the light lanthanides indicates that these lanthanides occupy the coordinaton site of Fe²⁺ by replacement. Both techniques are excellent in determining the very low concentration of lanthanides in geological materials, specifically garnet.     

Assessment of metals bound to marine plankton proteins and to dissolved proteins in seawater

Studies based on laser ablation–inductively coupled plasma-mass spectrometry (LA–ICP-MS) have been performed to assess metal bound to dissolved proteins and proteins from marine plankton after two-dimensional polyacrylamide gel electrophoresis (2D PAGE). Dissolved proteins were pre-concentrated from surface seawater (60 L) by tangential ultrafiltration with 10 kDa molecular weight cut-off (MWCO) membranes and further centrifugal ultrafiltration (10 kDa) before proteins isolation by methanol/chloroform/water precipitation. Proteins isolation from plankton was assessed after different trichloroacetic acid (TCA)/acetone and methanol washing stages, and further proteins extraction with a phenol solution. LA–ICP-MS analysis of the electrophoretic profiles obtained for dissolved proteins shows the presence of Cd, Cr, Cu, and Zn in five spots analyzed. These proteins exhibit quite similar molecular weights (within the 10–14 kDa range) and pIs (from 5.8 to 7.3). Cd, Cr, Cu, and Zn have also been found to be associated to proteins isolated from plankton samples. In this case, Cd has been found to be bound to proteins of quite different molecular weight (9, 13 and 22 kDa) and pIs (4.5, 5.2, 5.5, and 10). However, trace elements such as Cr, Cu and Zn appear to be mainly bound to plankton proteins of low molecular weight and variable pI.     

Carbon nanotubes as solid-phase extraction sorbents prior to atomic spectrometric determination of metal species: A review

New materials have significant impact on the development of new methods and instrumentation for chemical analysis. From the discovery of carbon nanotubes in 1991, single and multi-walled carbon nanotubes – due to their high adsorption and desorption capacities – have been employed as sorption substrates in solid-phase extraction for the preconcentration of metal species from diverse matrices. Looking for successive improvements in sensitivity and selectivity, in the past few years, carbon nanotubes have been utilized as sorbents for solid phase extraction in three different ways: like as-grown, oxidized and functionalized nanotubes. In the present paper, an overview of the recent trends in the use of carbon nanotubes for solid phase extraction of metal species in environmental, biological and food samples is presented. The determination procedures involved the adsorption of metals on the nanotube surface, their quantitative desorption and subsequent measurement by means of atomic spectrometric techniques such as flame atomic absorption spectrometry, electrothermal atomic absorption spectrometry or inductively coupled plasma atomic emission spectrometry/mass spectrometry, among others. Synthesis, purification and types of carbon nanotubes, as well as the diverse chemical and physical strategies for their functionalization are described. Based on 140 references, the performance and general properties of the applications of solid phase extraction based on carbon nanotubes for metal species atomic spectrometric determination are discussed.     

Solid Phase Extraction of Trace Metals in Seawater Using Morpholine Dithiocarbamate‐Loaded Amberlite XAD‐4 and Determination by ICP‐AES

Abstract

Application of morpholine dithiocarbamate (MDTC) coated Amberlite XAD‐4, for preconcentration of Cu(II), Cd(II), Zn(II), Pb(II), Ni(II) and Mn(II) by solid phase extraction and determination by inductively coupled plasma (ICP) atomic emission spectrometry (AES) was studied. The optimum pH values for quantitative sorption of Cu(II), Cd(II), Zn(II), Pb(II), Ni(II), and Mn(II) were 6.5–8.0, 7.0–8.5, 6.0–8.5, 6.5–8.5, 7.5–9.0, and 8.0–8.5, respectively. The metals were desorbed with 2 mol L^?1. The t_1/2 values for sorption of metal ions were 2.6, 2.9, 2.5, 2.6, 3.0, and 3.8 min respectively for Cu(II), Cd(II), Zn(II), Pb(II), Ni(II) and Mn(II). The effect of diverse ions on the determination of the previously named metals was studied. Simultaneous enrichment of the six metals was accomplished, and the method was applied for use in the determination of trace metal ions in seawater samples.     

Determination of phosphorus using capillary electrophoresis and micro-high-performance liquid chromatography hyphenated with inductively coupled plasma mass spectrometry for the quantification of nucleotides

We performed the quantification of phosphorus in deoxynucleotides using capillary electrophoresis (CE) and micro-HPLC (μHPLC) hyphenated with inductively coupled plasma mass spectrometry (ICP-MS). DNA and its component units have conventionally been determined by photometry; however, more selective and sensitive methods are needed for small biological samples. CE and μHPLC offer the advantages of good separation and small consumption of samples, and ICP-MS is a highly sensitive technique for the determination of a chemical element. Therefore, we have developed an interface device for combining CE and μHPLC with ICP-MS for quantifying nucleotides based on phosphorus content. The interface utilizes 4.5 μL/min for nebulizing and effective introduction of the sample into ICP. The samples of nucleotides and free phosphoric acid were well separated in the CE–ICP-MS measurement, and the calibration curves (1–100 μg/mL) of the nucleotides showed a linear (R² > 0.999) increase in intensity. Similarly, the samples of nucleotides were baseline separated using μHPLC–ICP-MS, and the calibration curves of the nucleotides were linear (R² > 0.998). The detection limits of these species and phosphorus in nucleotides using CE–ICP-MS and μHPLC–ICP-MS were 0.77–6.5 ng/mL and 4.0–6.5 ng/mL, respectively. These values were about one or two orders lower than those in a previous report. The sample volumes of these experiments were calculated to be about 10 nL and 50 nL per analysis. Therefore, these analytical methods have the potential to be useful for the determination of biological samples, such as DNA and RNA molecules.     

XPS,single crystal X-ray diffraction and cyclic voltammetric studies on 1,10-phenanthroline and 2,2′-bipyridine adducts of bis(piperidinecarbodithioato-S,S′)cadmium(II) with CdS4N2 environment – A stereochemical and electronic distribution investigation

(1,10-Phenanthroline)bis(piperidinecarbodithioato-S,S^′)cadmium(II), [Cd(pipdtc)₂(1,10-phen)] (1) and (2,2′-bipyridine)bis(piperidinecarbodithioato-S,S′)cadmium(II), [Cd(pipdtc)₂(bipy)] (2) adducts were prepared and the crystal structures are reported. Cd–S and Cd–N distances and the angles subtended at cadmium are almost the same in both complexes but the Cd–S distances in the adducts are longer than those in Cd(pipdtc)₂ (3) complexes due to the presence of an additional neutral ligand. Thioureide C–N distance in 1 and 2 are supported by νC–N bands observed at 1471 and 1470 cm⁻¹, respectively. S2p binding energies for the adducts show a significant reduction in value compared to the parent dithiocarbamate indicating the weakening of the Cd–S bond on adduct formation. The observed reduction in binding energy is due to the increased electron density on the metal in the adducts. The cyclic voltammetric study on the complexes also show an increase of electron density on cadmium in the adducts compared to Cd(pipdtc)₂.     

Simultaneous detection of zinc dimethyldithiocarbamate and zinc ethylenebisdithiocarbamate in cabbage leaves by capillary electrophoresis with inductively coupled plasma mass spectrometry

We report a simple and highly sensitive method for the simultaneous detection of trace zinc dimethyldithiocarbamate and zinc ethylenebisdithiocarbamate by capillary electrophoresis with inductively coupled plasma mass spectrometry. Zinc dimethyldithiocarbamate and zinc ethylenebisdithiocarbamate were chelated with trans‐1,2‐diaminocyclohexane‐N,N,N′,N′‐tetraacetic acid to form a macromolecule complex. Then, these two compounds were separated by α‐cyclodextrin‐modified capillary electrophoresis within 12 min at a separation voltage of 15 kV and measured by inductively coupled plasma mass spectrometry. The developed method is sensitive with detection limit of 1.9 and 3.0 ng Zn/mL for zinc dimethyldithiocarbamate and zinc ethylenebisdithiocarbamate, respectively. By means of ultrasound‐assisted extraction methods, zinc dimethyldithiocarbamate and zinc ethylenebisdithiocarbamate spiked into cabbage leaves were successfully extracted and determined with a relative standard deviation (n  = 5) ≤ 6% and a recovery of 95–107%.     

毛细管电泳-电感耦合等离子质谱联用的接口设计

描述了毛细管电泳电感耦合等离子体质谱(CE-ICP-MS)联用技术的单T型接口,自行设计了双T型接口,并对两接口的分析性能作了比较。解决了接口中的常见问题,使用节流阀减小自吸作用并降低了CE分离物的稀释倍数,排气阀使提升量保持稳定。经考察得知,采用自吸作用提升液流流量稳定,其重现性RSD小于5％;双T型接口较单T型接口对CE分离更有利。采用双T型接口联用时,CE分离La、Ce、Nd混合离子迁移时间RSD小于2％,MS信号RSD小于15％,且不同浓度样品经CE分离后其MS信号基本呈线性关系。     

Ultra-sensitive quantification of lysozyme based on element chelate labeling and capillary electrophoresis–inductively coupled plasma mass spectrometry

In this study, an ultra-sensitive method for the quantification of lysozyme based on the Gd³⁺ diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid labeling and capillary electrophoresis–inductively coupled plasma mass spectrometry (CE–ICP–MS) was described. The Gd³⁺-tagged lysozyme was effectively separated by capillary electrophoresis (CE) and sensitively determined by inductively coupled plasma mass spectrometry (ICP–MS). Based on the gadolinium-tagging and CE–ICP–MS, the lysozyme was determined within 12 min with an extremely low detection limit of 3.89 attomole (3.89 × 10⁻¹¹ mol L⁻¹ for 100 nL of sample injection) and a RSD < 6% (n = 5). The proposed method has been successfully used to detect lysozyme in saliva samples with a recovery of 91–106%, suggesting that our method is sensitive and reliable. The success of the present method provides a new potential for the biological assays and sensitive detection of low-abundant proteins.     

Development of an analytical procedure for the determination of polybrominated diphenyl ethers in environmental water samples by GC–ICP-MS

Polybrominated diphenyl ethers (PBDEs) are flame retardants, which due to their widespread use are frequently present as pollutants in the environment. In the EU Water Framework Directive (WFD) six PBDE congeners (BDE 28, BDE47, BDE 99, BDE 100, BDE 153 and BDE 154) are listed as priority substances. The uncertainty of the analytical method used for their determination in water samples at environmental quality standard (EQS) level (0.5 ng L⁻¹ for the ΣPBDEs) should be equal or less than 50% and the limit of quantification (LOQ) for ΣPBDEs below 0.15 ng L⁻¹. To meet these requirements, an analytical procedure for the determination of these six PBDEs in environmental water samples by gas chromatography–inductively coupled plasma mass spectrometry (GC–ICP-MS) was developed. The acidification of water samples to pH 2 maintained the stability of PBDEs for at least 20 days. The use of Tris–citrate buffer enabled efficient desorption of PBDEs from suspended particulate matter (SPM) and humic acids (HA), and their further quantitative solvent extraction into 2 mL of iso-octane. When 300 mL of water sample was used for analysis and the organic phase concentrated to 25 μL, the expanded uncertainty for determination of PBDEs at EQS level was found to be around 40% (a coverage factor for a confidence level of 95%, k = 2), and the LOQ for the ΣPBDEs 0.109 ng L⁻¹. Finally, to demonstrate the applicability of the newly developed GC–ICP-MS procedure, PBDEs were determined in river and sea water samples.     

Determination of mercurial species in fish by inductively coupled plasma mass spectrometry with anion exchange chromatographic separation

This work demonstrated the feasibility of mercury speciation analysis by anion exchange chromatographic separation with inductively coupled plasma mass spectrometry detection. For the first time, by complexing with the mobile phase containing 3-mercapto-1-propanesulfonate into negatively charged complexes, fast separation of inorganic mercury (Hg²⁺), monomethylmercury (MeHg), ethylmercury (EtHg) and phenylmercury (PhHg) was achieved within 5 min on a 12.5-mm strong anion exchange column. The detection limits for Hg²⁺, MeHg, EtHg and PhHg were 0.008, 0.024, 0.029 and 0.034 μg L⁻¹, respectively. The relative standard deviations of peak height and peak area (5.0 μg L⁻¹ for each Hg species) were all below 3%. The determined contents of Hg²⁺, MeHg and total Hg in a certified reference material of fish tissue by the proposed method were in good accordance with the certified values with satisfactory recoveries. The relative errors for determining MeHg and total mercury were −2.4% and −1.2%, respectively, with an acceptable range for spike recoveries of 94–101%. Mercury speciation in 11 fish samples were then analyzed after the pretreated procedure. The mercury contents in all fish samples analyzed were found compliant with the criteria of the National Standards of China.     

Speciation analysis of aluminium and aluminium fluoride complexes by HPIC-UVVIS

The study presents a new analytical method for speciation analysis in fractionation of aluminium fluoride complexes and free Al³⁺ in soil samples. Aluminium speciation was studied in model solutions and soil extract samples by means of high performance ion chromatography (HPIC) with UV-VIS detection using post-column reaction with tiron for the separation and detection of aluminium fluoride complex and Al³⁺ forms during one analysis. The paper presents particular stages of the chromatographic process optimization involving selecting the appropriate eluent strength, type of elution or concentration and quantity of derivatization reagent. HPIC was performed on a bifunctional analytical column Dionex IonPac CS5A. The use of gradient elution and the eluents A: 1 M NH₄Cl and B: water acidified to pH of eluent phase, enabled full separation of fluoride aluminium forms as AlF₂⁺, AlF₃⁰, AlF₄⁻ (first signal), AlF²⁺ (second signal) and form Al³⁺ in a single analytical procedure. The proposed new method HPIC-UVVIS was applied successfully in the quantitative and qualitative analysis of soil samples.     

The use of carbon nanofibers microcolumn preconcentration for inductively coupled plasma mass spectrometry determination of Mn,Co and Ni

Based on carbon nanofibers (CNFs) as a solid phase extraction adsorbent, a microcolumn preconcentration method coupled to inductively coupled plasma mass spectrometry (ICP–MS) was developed for the determination of trace elements (Mn, Co and Ni). The effect of various experimental parameters such as pH, sample flow rate and volume, elution solution and interfering ions on the retention of the studied ions have been investigated systematically. During all the steps of the experimental process, Mn, Co and Ni could be quantitatively sorbed on the microcolumn containing CNFs in the range of pH 6.0–9.0, and then eluted completely with 0.5 mol ml^− 1 HNO₃. A preconcentration factor of 150-fold was obtained. The detection limits for Mn, Co and Ni were 40, 0.4 and 8.0 pg ml^− 1, respectively, with relative standard deviations less than 6.0%. In order to validate the proposed method, two certified reference materials of human hair (GBW 07601) and mussel (GBW 08571), and water sample were analyzed with satisfactory results. The recoveries were between 95.0 and 114%.     

A modified sequential extraction method for arsenic fractionation in sediments

A modified sequential extraction method was developed to characterize arsenic (As) associated with different solid constituents in surficial deposits (sediments), which are unconsolidated glacial deposits overlying bedrock. Current sequential extraction methods produce a significant amount of unresolved As in the residual fraction, but our proposed scheme can fractionate >90% of the As present in sediments. Sediment samples containing different As concentrations (3–35 μg g⁻¹) were used to assess the developed method. The pooled amount of As recovered from all the fractions using the developed method was similar (83–122%) to the total As extracted by acid digestion. The concentrations of As in different fractions using the developed scheme were comparable (89–106%) to the As fractions obtained by other existing methods. The developed method was also evaluated for the sequential extraction of other metals such as copper (Cu), cobalt (Co), chromium (Cr) and strontium (Sr) in the sediment samples. The pooled concentrations of these four individual metals from all the fractions were similar (96–104%) to their total concentrations extracted by acid digestion. During method development, we used extractants that did not contain chloride to eliminate formation of polyatomic ions of argon chloride (⁴⁰Ar³⁵Cl) that interfered with ⁷⁵As when analyzed using inductively coupled plasma mass spectrometer (ICP-MS). The results suggest that the developed method can reliably be employed for complete As and other metals’ fractionation in sediments using ICP-MS.