Seawater Reference Material Research Articles

Simultaneous determinations of zirconium, hafnium, yttrium and lanthanides in seawater according to a co-precipitation technique onto iron-hydroxide

Very low concentrations (pg mL(-1) or sub-pg mL(-1) level) along with the high salinity are the main problems in determining trace metal contents in seawater. This problem is mainly considered for investigations of naturally occurring YLOID (Y and Lanthanides) and Zr and Hf in order to provide precise and accurate results. The inductively coupled plasma mass spectrometry (ICP-MS), both in high and low resolution, offers many advantages including simultaneous analyses of all elements and their quantitative determination with detection limits of the order of pg mL(-1). However in the analysis of YLOID in seawater, a better determination needs an efficient combination of ICP-MS measurement with a pre-concentration technique. To perform an ultra-trace analysis in seawater, we have validated an analytical procedure involving an improved modified co-precipitation on iron hydroxides to ensure the simultaneous quantitative recovery of YLOID, Zr and Hf contents with measurement by a quadrupole ICP-MS. The validity of the method was assessed through a series of co-precipitation experiments and estimation of several quality control parameters for method validation, namely working range and its linearity, detection limit, quantification limit, precision and spike recoveries, and the methodological blank choice, are introduced, evaluated and discussed. Analysis of NASS-6, is the first report on the latest seawater reference material for YLOID, hafnium and zirconium.

Determination of isotopic composition of dissolved copper in seawater by multi-collector inductively coupled plasma mass spectrometry after pre-concentration using an ethylenediaminetriacetic acid chelating resin

Copper is an essential trace metal that shows a vertical recycled-scavenged profile in the ocean. To help elucidate the biogeochemical cycling of Cu in the present and past oceans, it is important to determine the distribution of Cu isotopes in seawater. However, precise isotopic analysis of Cu has been impaired by the low concentrations of Cu as well as co-existing elements that interfere with measurements by multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The objective of this study is to develop a simple Cu pre-concentration method using Nobias-chelate PA1 resin (Hitachi High Technologies). This extraction followed by anion exchange, allows precise analysis of the Cu isotopic composition in seawater. Using this method, Cu was quantitatively concentrated from seawater and >99.9999% of the alkali and alkaline earth metals were removed. The technique has a low procedural blank of 0.70ng for Cu for a 2L sample and the precision of the Cu isotopic analysis was ±0.07‰ (±2SD, n=6). We applied this method to seawater reference materials (i.e., CASS-5 and NASS-6) and seawater samples obtained from the northwestern Pacific Ocean. The range of dissolved δ65Cu was 0.40–0.68‰.

Selective hydride generation- cryotrapping- ICP-MS for arsenic speciation analysis at picogram levels: analysis of river and sea water reference materials and human bladder epithelial cells.

An ultra sensitive method for arsenic (As) speciation analysis based on selective hydride generation (HG) with preconcentration by cryotrapping (CT) and inductively coupled plasma- mass spectrometry (ICP-MS) detection is presented. Determination of valence of the As species is performed by selective HG without prereduction (trivalent species only) or with L-cysteine prereduction (sum of tri- and pentavalent species). Methylated species are resolved on the basis of thermal desorption of formed methyl substituted arsines after collection at -196°C. Limits of detection of 3.4, 0.04, 0.14 and 0.10 pg mL-1 (ppt) were achieved for inorganic As, mono-, di- and trimethylated species, respectively, from a 500 μL sample. Speciation analysis of river water (NRC SLRS-4 and SLRS-5) and sea water (NRC CASS-4, CASS-5 and NASS-5) reference materials certified to contain 0.4 to 1.3 ng mL-1 total As was performed. The concentrations of methylated As species in tens of pg mL-1 range obtained by HG-CT-ICP-MS systems in three laboratories were in excellent agreement and compared well with results of HG-CT-atomic absorption spectrometry and anion exchange liquid chromatography- ICP-MS; sums of detected species agreed well with the certified total As content. HG-CT-ICP-MS method was successfully used for analysis of microsamples of exfoliated bladder epithelial cells isolated from human urine. Here, samples of lysates of 25 to 550 thousand cells contained typically tens pg up to ng of iAs species and from single to hundreds pg of methylated species, well within detection power of the presented method. A significant portion of As in the cells was found in the form of the highly toxic trivalent species.

Selective hydride generation-cryotrapping-ICP-MS for arsenic speciation analysis at picogram levels: analysis of river and sea water reference materials and human bladder epithelial cells

Selective hydride generation-cryotrapping-ICP-MS for arsenic speciation analysis at picogram levels: analysis of river and sea water reference materials and human bladder epithelial cells

δ98/95Mo values and Molybdenum Concentration Data for NIST SRM 610, 612 and 3134: Towards a Common Protocol for Reporting Mo Data

Molybdenum concentration and δ98/95Mo values for NIST SRM 610 and 612 (solid glass), NIST SRM 3134 (lot 891307; liquid) and IAPSO seawater reference material are presented based on comparative measurements by MC‐ICP‐MS performed in laboratories at the Universities of Bern and Oxford. NIST SRM 3134 and NIST SRM 610 and 612 were found to have identical and homogeneous 98Mo/95Mo ratios at a test portion mass of 0.02 g. We suggest, therefore, that NIST SRM 3134 should be used as reference for the δ–Mo notation and to employ NIST SRM 610 or 612 as solid silicate secondary measurement standards, in the absence of an isotopically homogeneous solid geological reference material for Mo. The δ98/95MoJMC Bern composition (Johnson Matthey ICP standard solution, lot 602332B as reference) of NIST SRM 3134 was 0.25 ± 0.09‰ (2s). Based on five new values, we determined more precisely the mean open ocean δ98/95MoSRM 3134 value of 2.09 ± 0.07‰, which equals the value of δ98/95MoJMC Bern of 2.34 ± 0.07‰. We also refined the Mo concentration data for NIST SRM 610 to 412 ± 9 μg g−1 (2s) and NIST SRM 612 to 6.4 ± 0.7 μg g−1 by isotope dilution. We propose these concentration data as new working values, which allow for more accurate in situ Mo determination using laser ablation ICP‐MS or SIMS.

Intercalibration of Cd and Pb concentration measurements in the northwest Pacific Ocean

Dissolved and total Cd and Pb concentration measurements in seawater were intercalibrated using 33 samples collected on the fourth cruise of the Intergovernmental Oceanographic Commission's (IOC‐4) Global Investigation of Pollution in the Marine Environment (GIPME) in the northwest Pacific Ocean, as well as in three seawater reference materials (SAFe S1, SAFe D2, and NASS‐5). Laboratories from Florida State University (FSU), University of California at Santa Cruz (UCSC), and University of Southern Mississippi (USM) participated in the Pb intercalibration, and two of them (FSU and UCSC) participated in the Cd intercalibration. While each of the laboratories employed different extraction techniques before analysis by inductively coupled plasma—mass spectrometry (ICP‐MS), the measurements of Cd and Pb concentrations for the IOC‐4 samples agreed to within 4% and 15%, respectively, and those of the reference materials agreed to within 13% and 8%, respectively. This successful intercalibration demonstrates that there now are multiple techniques available for accurately measuring Cd and Pb concentrations in seawater.

Determination of plutonium isotopes in seawater reference materials using isotope-dilution ICP-MS

We analyzed the activities of 239Pu, 240Pu, 239+240Pu, 241Pu, the ratio of number of atoms (atom ratio) for 240Pu/239Pu, and the activity ratio of 241Pu/239+240Pu in seawater reference materials, IAEA-443 and IAEA-381, using a highly sensitive isotope dilution sector field inductively coupled plasma mass spectrometry method. With a mean chemical yield of 65% determined with 242Pu as a tracer, we found that the experimentally established values in IAEA-443 for 239Pu, 240Pu, 241Pu and 239+240Pu activities are almost the same as those in IAEA-381. Regarding the 239+240Pu activity, we provided the most precise and accurate result among the twelve laboratories, which participated in the interlaboratory comparison. In addition, for the 240Pu/239Pu atom ratio, our results for IAEA-381 (0.2315±0.0008) and IAEA-443 (0.2325±0.0008) are in good agreement with the IAEA information value (0.229±0.006), but have much smaller uncertainty. Since the new seawater reference material, IAEA-443, is commercially available, it can be used not only for method validation for seawater plutonium isotope ratio and activity analysis, but also for more general use as a plutonium isotope standard for mass discrimination correction for other environmental samples.

A new methodology for precise cadmium isotope analyses of seawater

Previous studies have revealed considerable Cd isotope fractionations in seawater, which can be used to study the marine cycling of this micronutrient element. The low Cd concentrations that are commonly encountered in nutrient-depleted surface seawater, however, pose a particular challenge for precise Cd stable isotope analyses. In this study, we have developed a new procedure for Cd isotope analyses of seawater, which is suitable for samples as large as 20 L and Cd concentrations as low as 1 pmol/L. The procedure involves the use of a (111)Cd-(113)Cd double spike, co-precipitation of Cd from seawater using Al(OH)(3), and subsequent Cd purification by column chromatography. To save time, seawater samples with higher Cd contents can be processed without co-precipitation. The Cd isotope analyses are carried out by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The performance of this technique was verified by analyzing multiple aliquots of a large seawater sample that was collected from the English Channel, the SAFe D1 seawater reference material, and several samples from the GEOTRACES Atlantic intercalibration exercise. The overall Cd yield of the procedure is consistently better than 85% and the methodology can routinely provide ε (114/110)Cd data with a precision of about ±0.5 ε (2sd, standard deviation) when at least 20-30 ng of natural Cd is available for analysis. However, even seawater samples with Cd contents of only 1-3 ng can be analyzed with a reproducibility of about ±3 to ±5 ε. A number of experiments were furthermore conducted to verify that the isotopic results are accurate to within the quoted uncertainty.

Determination of ultratrace levels of dissolved metals in seawater by reaction cell inductively coupled plasma mass spectrometry after ammonia induced magnesium hydroxide coprecipitation

A method for the determination of ultratrace amounts of Cr, Fe, Mn, Pb and Zn in seawater has been developed. It combined the low-blank magnesium hydroxide coprecipitation procedure with quadrupole inductively coupled plasma mass spectrometry and used the dynamic reaction cell technique to resolve the polyatomic interferences arising from the residual matrix, the solvent and plasma gases. Detection limits (3 σ B, n = 10) for Cr, Fe, Mn, Pb and Zn were 0.02, 0.10, 0.01, 0.002 and 0.19 nM, respectively, using 50 mL of seawater sample. The accuracy of the analytical procedure was verified by the analysis of the seawater reference materials CASS-4, NASS-5, SAFe D2 and SAFe S. The analytical precision ranged from 3% to 16% ( n = 6), with a sample throughput of about 6 samples h −1.

Speciation of mercury in water samples by dispersive liquid–liquid microextraction combined with high performance liquid chromatography-inductively coupled plasma mass spectrometry

The dispersive liquid–liquid microextraction (DLLME) combined with high performance liquid chromatography-inductively coupled plasma mass spectrometry for the speciation of mercury in water samples was described. Firstly methylmercury (MeHg +) and mercury (Hg 2+) were complexed with sodium diethyldithiocarbamate, and then the complexes were extracted into carbon tetrachloride by using DLLME. Under the optimized conditions, the enrichment factors of 138 and 350 for MeHg + and Hg 2+ were obtained from only 5.00 mL sample solution. The detection limits of the analytes (as Hg) were 0.0076 ng mL −1 for MeHg + and 0.0014 ng mL −1 for Hg 2+, respectively. The relative standard deviations for ten replicate measurements of 0.5 ng mL −1 MeHg + and Hg 2+ were 6.9% and 4.4%, respectively. Standard reference material of seawater (GBW(E)080042) was analyzed to verify the accuracy of the method and the results were in good agreement with the certified values. Finally, the developed method was successfully applied for the speciation of mercury in three environmental water samples.

MC‐ICP‐MS Isotope Measurements with Direct Injection Nebulisation (d‐DIHEN): Optimisation and Application to Boron in Seawater and Carbonate Samples

We report here an optimisation of the demountable direct injection high efficiency nebuliser (d‐DIHEN) for isotopic measurements with a Neptune (ThermoFisher Scientific, Bremen, Germany) multi‐collector inductively coupled plasma‐mass spectrometer (MC‐ICP‐MS) and describe a method for boron isotopic ratio determination. With direct injection nebulisation 100% of the analyte was introduced into the ICP‐MS plasma and wash times were drastically reduced for elements such as boron and thorium. Compared to the classical stable introduction system (SIS: double Scott/cyclonic spray chamber), sensitivity for boron was 2–5 times higher with d‐DIHEN and wash times up to ten times shorter. Repeatability of 11B/10B sample‐calibrator bracketing measurements reached 0.25‰ (2s) for seawater and coral samples. Method accuracy and reproducibility were tested on mixed reference solutions having δ11B values in the ranges −90 to +40‰ and −2 to +2.5‰, demonstrating our ability to distinguish δ11B values with differences of only 0.25‰. The international seawater reference material NRCC NASS‐5 (National Research Council, Ottawa, Canada), analysed in different sessions over a 10‐month period, yielded an average δ11B value of +39.89 ± 0.25‰, in the upper range of previously published seawater values. A comparison between δ11B determined by d‐DIHEN MC‐ICP‐MS and positive‐TIMS (P‐TIMS) for four modern corals showed an excellent agreement (with bias of less than 0.4‰).

Accurate and High-Precision Determination of Boron Isotopic Ratios at Low Concentration by MC-ICP-MS (Neptune)

We report an approach for the accurate and reproducible measurement of boron isotope ratios in natural waters using an MC-ICP-MS (Neptune) after wet chemistry sample purification. The sample matrix can induce a drastic shift in the isotopic ratio by changing the mass bias. It is shown that, if no purification is carried out, the direct measurement of a seawater diluted one hundred times will induce an offset of −7‰ in the isotopic ratio, and that, for the same concentration, the greater the atomic mass of the matrix element, the greater the bias induced. Whatever the sample, it is thus necessary to remove the matrix. We propose a method adapted to water samples allowing purification of 100 ng of boron with a direct recovery of boron in 2 ml of 3% v/v HNO3, which was our working solution. Boron from the International Atomic Energy Agency IAEA-B1 seawater reference material and from the two groundwater reference materials IAEA-B2 and IAEA-B3, was chemically purified, as well as boron from the certified reference material NIST SRM 951 as a test. The reproducibility of the whole procedure (wet chemistry and MC-ICP-MS measurement) was ± 0.4‰ (2s). Accuracy was verified by comparison with positive-TIMS values and with recommended values. Seawater, being homogeneous for boron isotope ratios, is presently the only natural water material that is commonly analysed for testing accuracy worldwide. We propose that the three IAEA natural waters could be used as reference samples for boron isotopes, allowing a better knowledge of their isotopic ratios, thus contributing to the certification of methods and improving the quality of the boron isotopic ratio measurements for all laboratories. Nous présentons ici une approche permettant la mesure juste et reproductible des rapports isotopiques du bore dans les eaux naturelles par l’utilisation d’un MC-ICP-MS (Neptune) après purification chimique de l’échantillon. Comme nous le démontrons, la matrice de l’échantillon peut induire un fractionnement important des rapports isotopiques. La mesure directe d’une eau de mer non purifiée, simplement diluée cent fois, entraine une différence de −7‰ sur le rapport isotopique. Il est également montré, qu’à teneur identique, plus l’élément est de masse atomique élevée, plus le biais sera important. Quel que soit l’échantillon, il s’avère nécessaire de le purifier. Nous proposons une méthode adaptée aux eaux naturelles permettant la purification de 100 ng de bore avec une récupération directe du bore dans 2 ml de 3% v/v HNO3 qui est la solution utilisée en routine pour la mesure sur notre MC-ICP-MS. La purification chimique du bore a été réalisée sur une eau de mer (IAEA-B1) et deux eaux souterraines (IAEA-B2 et IAEA-B3) ainsi que sur le matériau de référence NIST SRM 951. La reproductibilité de la procédure (purification chimique et analyse au NEPTUNE) est de ± 0.4‰ (2s). La justesse est vérifiée par comparaison avec des valeurs obtenues en P-TIMS ainsi qu’avec les valeurs recommandées. L’eau de mer étant homogène pour les rapports isotopiques du bore, elle est actuellement la seule eau naturelle analysée couramment pour tester la justesse des mesures au sein de différents laboratoires. Nous proposons que les trois eaux naturelles de l’IAEA soient utilisées en tant que solutions de référence pour les isotopes du bore, permettant ainsi une meilleure connaissance de leur rapport isotopique, et par conséquent aidant à la certification des méthodes et améliorant la qualité de la mesure des rapports isotopiques du bore dans les différents laboratoires.

Microchip based sample treatment device interfaced with ICP-MS for the analysis of transition metals from environmental samples

A downscaled solid phase (SPE) device applicable for sample preparation prior to ICP-MS monitoring, have been constructed making use of the lab on a chip concept. Standard photolithography and wet chemical etching were used to fabricate glass microfluidic devices accommodating three microchannels, each of them incorporating a defined section that could be packed with SPE materials; selective chelating resin. The microfluidic device was interfaced with the ICP-MS instrument throughout a low flow rate concentric nebuliser using a Teflon connector, and coupled with a flow injection manifold delivering samples and reagents via a manually operated splitting valve. The feasibility of the miniaturized prototype to perform SPE of trace metals was proved by analyzing trace metals, Cd, Co, and Ni, in seawater reference materials; CASS-2 and SLEW-1. The obtained result was in good agreement with the certified values. The device could be used as a remote miniaturized sample treatment for field work.

Optimization of experimental parameters in the determination of zinc in sea water by adsorptive stripping voltammetry

A procedure for the determination of zinc in sea water by square wave adsorptive stripping voltammetry (SWAdSV) using 8-hydroxyquinoline (oxine) as an adsorbing and complexing agent has been optimized. First, a univariate study of the Zn-Ox complex peak current as a function of pH was carried out choosing values at which adequate currents were obtained. Then, selection of the experimental conditions was made using a multivariate experimental design. Variables like pH, oxine concentration (Cox), adsorption time (tads) and adsorption potential (Eads) were optimized. The first optimization step was a 24 factorial design with 16 measurements made choosing high and low levels, and three measurements at the central point (Zn(II) 10.0 μg L-1). Analysis of variance showed that pH and Cox were the most significant factors, while tads and Eads were not significant and were kept constant in later measurements. Next, to find the optimum values for pH and Cox a 22 + star factorial design was used. The best experimental parameters were pH = 6.0; Cox = 25 μmol L-1; tads = 10 s and Eads = -0.70 V. Under these conditions the peak current was proportional to the concentration of zinc over the 0.1-48.0 μg L-1 range, with a detection limit of 0.05 μg L-1. Reproducibility for 5.0 μg mL-1 Zn(II) solution was 1.9 % (n = 16). The method was validated using spiked synthetic sea water (ASTM D665), sea water reference material (CRM-SW. Zn 5 μg kg-1) and fortified water reference material (GBW08607. Zn 5 mg kg-1) with satisfactory results. Finally, the method was successfully applied to the determination of Zn(II) in sea water samples without prior treatment.

Development of a Field Preconcentration/Elution Unit for Routine Determination of Dissolved Metal Concentrations by ICP‐OES in Marine Waters: Application for Monitoring of the New Caledonia Lagoon

An iminodiacetate chelating resin was optimised for the rapid determination of Co, Cu, Fe, Mn and Ni in seawater. Using inexpensive, high‐capacity, reusable cartridges allowed high flow rates of up to 25 ml min−1. High preconcentration factors, of up to 500, were obtained in order to analyse samples using an ICP‐OES. The requirement for a buffer was eliminated due to the high tolerance of the ICP‐OES to interfering matrix elements, thereby further reducing the potential for contamination. Quantification limits in seawater were: Co = 6 ng l−1, Cu = 8 ng l−1, Fe = 6 ng l−1, Mn = 5 ng l−1 and Ni = 6 ng l−1. The method was verified by the analysis of near shore seawater (CASS‐4) and open ocean seawater (NASS‐5) reference materials. In order to satisfy the high sampling demands using the iminodiacetate cartridges, a portable off‐line preconcentration unit was developed for routine analysis. The multi‐channel preconcentration unit, was capable of treating up to eight samples simultaneously with concentrating times as little as 30 minutes. The technique was also used to determine dissolved metals in fresh and interstitial waters. The technique has been successfully used in a number of environmental studies and impact assessments to evaluate the effects of mining on the New Caledonian lagoon.

Magnesium Isotope Compositions of Natural Reference Materials

This study presents a chemical protocol for the separation of Mg that is particularly adapted to alkali‐rich samples (granite, soil, plants). This protocol was based on a combination of two pre‐existing methods: transition metals were first removed from the sample using an AG‐MP1 anion‐exchange resin, followed by the separation of alkalis (Na, K) and bivalent cations (Ca2+, Mn2+ and Sr2+) using a AG50W‐X12 cation‐exchange resin. This procedure allowed Mg recovery of ∼ 10 0 ± 8%. The [Σcations]/[Mg] molar ratios in all of the final Mg fractions were lower than 0.05. The Mg isotope ratios of eleven reference materials were analysed using two different MC‐ICP‐MS instruments (Isoprobe and Nu Plasma). The long‐term reproducibility, assessed by repeated measurements of Mg standard solutions and natural reference materials, was 0.14‰. The basalt (BE‐N), limestone (Cal‐S) and seawater (BCR‐403) reference materials analysed in this study yielded δ26Mg mean values of −0.28 ± 0.08‰, −4.37 ± 0.11‰ and −0.89 ± 0.10‰ respectively, in agreement with published data. The two continental rocks analysed, diorite (DR‐N) and granite (GA), yielded δ26Mg mean values of −0.50 ± 0.08‰ and −0.75 ± 0.14‰, respectively. The weathering products, soil (TILL‐1) and river water (NIST SRM 1640), gave δ26Mg values of −0.40 ± 0.07‰ and −1.27 ± 0.14‰, respectively. We also present, for the first time, the Mg isotope composition of bulk plant and organic matter. Rye flour (BCR‐381), sea lettuce (Ulva lactuva) (BCR‐279), natural hairgrass (Deschampsia flexuosa) and lichen (BCR‐482) reference materials gave δ26Mg values of −1.10 ± 0.14‰, −0.90 ± 0.19‰, −0.50 ± 0.22‰ and −1.15 ± 0.27‰ respectively. Plant δ26Mg values fell within the range defined by published data for chlorophylls.

Determination of sub-nanomolar levels of iron in sea-water using reaction cell inductively coupled plasma mass spectrometry after Mg(OH)2 coprecipitation

A new procedure for the determination of iron in sea-water at sub-nanomolar concentration levels was developed. The method applied the low-blank magnesium hydroxide co-precipitation procedure in combination with quadrupole ICP-MS and used the dynamic reaction cell technique to resolve the polyatomic interferences arising from the residual matrix and the solvent. Although the interference-free determination at m/z = 56 could be obtained by using methane as the reaction gas, the best signal-to-background ratio was achieved by using ammonia and performing the measurements at m/z = 54. Accurate quantification of low levels of iron at m/z = 54 also required the mathematical correction for the isobaric interference due to the occurrence of chromium. The main analytical figures of the optimized method were evaluated, with special attention to the determination of the procedural, reagent and field blanks. A detection limit as low as 0.09 nM was achieved, using a pre-concentration ratio of 10. The accuracy of the analytical procedure was evaluated by the analysis of the sea-water reference materials CASS-4, NASS-5, SAFe D2 and SAFe S1, having certified concentration values ranging from 12.8 nM to about 0.1 nM. The analytical precision for replicated analyses of the CRMs ranged from 1.3% to 14% (n = 7). Finally, the developed procedure was applied to a number of open-ocean sea-water samples from the Ross Sea (Southern Ocean, Antarctica)

Magnetic nano-adsorbent integrated with lab-on-valve system for trace analysis of multiple heavy metals

A novel system for trace analysis of multiple heavy metals was developed wherein we have integrated a magnetic nano-adsorbent with a lab-on-valve system and coupled this to an inductively coupled plasma mass spectrometer. The magnetic nano-adsorbent was prepared by surface modification of iron-based magnetic nanoparticles with polyacrylic acid (MNPs-PAA). The MNPs-PAA possessing the superparamagnetic nature of MNPs could be controllably immobilized in PTFE tubing by an external magnetic force. The high surface density of PAA (3.30 × 1011 molecules cm−2) on MNPs-PAA significantly reduced the amounts of adsorbent needed for adsorption of heavy metals (Mn2+, Co2+, Cu2+, Zn2+, and Pb2+). A detection limit of 0.04–0.06 µg L−1 (except 0.6 µg L−1 for Cu2+ and Zn2+), a precision smaller than 4% (RSD, n = 3), and a linear range of 0.5–50 µg L−1 were obtained by directly injecting an aliquot of 20 µL fortified standard solution analyzed at 5 min per sample. The accuracy was evaluated by analyzing certified reference materials of SRM 2670a (trace elements in urine, low level) and CASS-2 (nearshore seawater reference material for trace metals). Good agreement between the measured and certified values demonstrated that the system is useful for trace analysis of multiple heavy metals in environmental and biological aqueous samples. The potential of integrating functionalized nano-materials to improve the performance of existing analytical systems as an alternative approach to green analytical chemistry is foreseen.

Sample Pretreatment Using Chitosan-based Chelating Resin for the Determination of Trace Metals in Seawater Samples by Inductively Coupled Plasma-Mass Spectrometry

A sample-pretreatment method using a chitosan-based chelating resin, ethylenediamine-N,N,N'-triacetate-type chitosan (EDTriA-type chitosan), was developed for the preconcentration of trace metals in seawater and separation of the seawater matrix prior to their determination by inductively coupled plasma-mass spectrometry (ICP-MS). The resin showed very good adsorption for transition metals and rare-earth elements without any interference from alkali and alkaline-earth metals in an acidic media. In the proposed method, an aliquot of a 50-mL sample at pH 4 was used. Metals adsorbed on the resin were eluted using 10 mL of 1 M nitric and measured by ICP-MS. The method was evaluated by the analysis of NASS-5 seawater reference materials for trace metals. Good agreement was obtained for most metals, which indicates that by the proposed pretreatment using the synthesized resin, seawater samples can be favorably measured by ICP-MS.

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 Cu 2+ with silk fibroin at pH 6.0 was investigated and a novel on-line procedure for separation/preconcentration of Cu 2+ 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.