Determination of 232Th in seawater by ICP-MS after preconcentration and separation using a chelating resin

This article describes an analytical method for the separation, preconcentration and determination of ²³²Th in seawater samples at sub-ng/L levels using a NOBIAS CHELATE PA1 resin and a sector field (SF) inductively coupled plasma mass spectrometer (ICP-MS). The resin showed excellent adsorption of ²³²Th at a low pH of 2.4 ± 0.4 in a relatively small volume (200 mL) of seawater. ²³²Th adsorbed on the resin was easily eluted using 5 mL of 0.8 M HNO₃. An enrichment factor of 40 was achieved for ²³²Th analysis. Ethylenediamine-tetraacetic acid disodium salt dehydrate (EDTA) was used to investigate the effect of ²³²Th-binding organic ligand on the retention of ²³²Th on the chelating resin. Results obtained using acidified samples (pH of 2.4 ± 0.4) showed EDTA had no significant effect on ²³²Th recovery, indicating that at this low pH, ²³²Th was dissociated from the ²³²Th-binding organic ligand and quantitatively retained on the NOBIAS CHELATE PA1 resin. The developed analytical method was characterized by a separation and preconcentration taking approximately 4 h and a low detection limit of 0.0038 ng/L for ²³²Th, and was successfully applied to the determination of ²³²Th in seawater samples collected from coastal areas, Japan.     

Optical fibre reflectance sensor for the determination and speciation analysis of iron in fresh and seawater samples coupled to a multisyringe flow injection system

A novel optical fibre reflectance sensor coupled to a multisyringe flow injection system (MSFIA) for the determination and speciation analysis of iron at trace level using chelating disks (iminodiacetic groups) is proposed. Once iron(III) has been retained onto a chelating disk, an ammonium thiocyanate stream is injected in order to form the iron(III)-thiocyanate complex which is spectrophotometrically detected at 480 nm. Iron(III) is eluted with 2 M hydrochloric acid so that the chelating disk is regenerated for subsequent experiments. The determination of total iron is achieved by the on-line oxidation of iron(II) to iron(III) with a suitable hydrogen peroxide stream.A mass calibration was feasible in the range from 0.001 to 0.25 μg. The detection limit (3s_b/S) was 0.001 μg. The repeatability (RSD), calculated from nine replicates using 1 ml injections of a 0.1 mg/l concentration, was 2.2%. The repeatability between five chelating disks was 3.6%. The applicability of the proposed methodology in fresh and seawater samples has been proved.The proposed technique has been validated by replicate analysis (n = 4) of certified reference materials of water with satisfactory results.     

Determination of iron and copper in seawater at pH 1.7 with a new commercially available chelating resin, NTA Superflow

The use of a commercially available chelating resin with NTA-type functional groups for concentration of trace metals from seawater is described. Trace metal recoveries from this NTA Superflow chelating resin are pH dependent. At a pH of ≤2 only iron(III) and copper are quantitatively recovered from the resin. Iron(II) cannot be quantitatively recovered from this resin below a pH of 5. However, oxidation of acidified seawater samples (pH 1.7) with H₂O₂ prior to loading onto the resin has been demonstrated to allow quantitative recovery of total dissolved iron. Deferrioxamine and Rhodoturlic Acid, two commercially available siderophores were used to investigate the effect of strong Fe(III)-binding organic ligands on the ability to retain iron at different pH values. Acidification of seawater samples to pH 1.7 dissociates the iron complexed to these organic ligands, thereby allowing total dissolved iron and copper to be determined. Acidified samples from Monterey Bay were analyzed by a flow injection method coupled to ICP-SFMS detection using the NTA Superflow resin in the pre-concentration step. Results from this study show that when seawater samples are stored acidified (pH 1.7) over time, a portion of iron(III) is reduced to iron(II), thus necessitating the use of H₂O₂ to reoxidize the Fe(II) to Fe(III) prior to analysis. Total dissolved concentrations of iron and copper can be directly obtained on seawater samples at pH 1.7 with this method, eliminating the need to buffer the sample to a higher pH prior to column loading. This resin has the potential to be used in shipboard or in situ flow injection methods.     

An off-line automated preconcentration system with ethylenediaminetriacetate chelating resin for the determination of trace metals in seawater by high-resolution inductively coupled plasma mass spectrometry

A novel automated off-line preconcentration system for trace metals (Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) in seawater was developed by improving a commercially available solid-phase extraction system SPE-100 (Hiranuma Sangyo). The utilized chelating resin was NOBIAS Chelate-PA1 (Hitachi High-Technologies) with ethylenediaminetriacetic acid and iminodiacetic acid functional groups. Parts of the 8-way valve made of alumina and zirconia in the original SPE-100 system were replaced with parts made of polychlorotrifluoroethylene in order to reduce contamination of trace metals. The eluent pass was altered for the back flush elution of trace metals. We optimized the cleaning procedures for the chelating resin column and flow lines of the preconcentration system, and developed a preconcentration procedure, which required less labor and led to a superior performance compared to manual preconcentration (Sohrin et al. [5]). The nine trace metals were simultaneously and quantitatively preconcentrated from ∼120 g of seawater, eluted with ∼15 g of 1 M HNO₃, and determined by HR-ICP-MS using the calibration curve method. The single-step preconcentration removed more than 99.998% of Na, K, Mg, Ca, and Sr from seawater. The procedural blanks and detection limits were lower than the lowest concentrations in seawater for Mn, Ni, Cu, and Pb, while they were as low as the lowest concentrations in seawater for Al, Fe, Co, Zn, and Cd. The accuracy and precision of this method were confirmed by the analysis of reference seawater samples (CASS-5, NASS-5, GEOTRACES GS, and GD) and seawater samples for vertical distribution in the western North Pacific Ocean.     

Shipboard analysis of picomolar levels of manganese in seawater by chelating resin concentration and chemiluminescence detection

A new shipboard analytical method for determining picomolar levels of manganese in seawater has been developed. The method is based on a combination of chelating resin column extraction and improved chemiluminescence (CL) detection in a closed flow system. In this method, manganese in sample solution is selectively collected on newly-developed iminodiacetate-immobilized chelating resin, and then eluted with acidic solution containing hydrogen peroxide. The resulting eluent is mixed with luminol solution and aqueous ammonia after removal of iron ions by a chelating resin column, and then the mixture is introduced into the CL cell. The manganese concentration is obtained from the CL intensity. The detection limit (3SD) of manganese is 5 pmol L^–1 from 9 mL of seawater sample. The method was applied to seawater samples collected at the Okinawa Trough.     

Interactions of thorium isotopes with colloidal organic matter in oceanic environments

The phase speciation of thorium and consequences for the residence times of colloids have been examined in seawater of the Middle Atlantic Bight (MAB) and the Gulf of Mexico. Two fractions of colloidal organic matter (COM), 0.2 μm > COM₁ > 1 kD and 0.2 μm > COM₁₀ > 10 kD, were sampled using cross-flow ultrafiltration techniques and measured for their ²³⁴Th activity and organic carbon concentration. The ratios of mass concentrations of COM₁ to those of suspended particulate matter were as high as 10 in the MAB and 6–34 in the Gulf of Mexico. Higher concentrations of colloids may be of great importance in the biogeochemical cycling of many particle-reactive nuclides or trace elements owing to their high specific surface area and complexation capacity. A significant fraction of ²³⁴Th in the traditionally defined “dissolved” pool was found to be associated with colloids. On average, about 10% of “dissolved” ²³⁴Th was in the colloidal fraction of sizes between 10 kDa and 0.2 μm, and 50% was in the 1 kDa-0.2 μm fraction. Values of the partition coefficients [K_c: (0.5−4) × 10⁶ ml g⁻¹ for K_c1 and (0.5−7) × 10⁶ ml g⁻¹ for K_c10] of ²³⁴Th between truly dissolved (<1 kDa) and colloidal fractions approximated those for Th-particle interactions [K_p: (0.3−10) × 10⁶ ml g⁻¹], indicating that colloid and suspended particle surface sites are similar. The distribution of ²³⁴Th between dissolved, colloidal, and particulate phases was broadly similar to that of organic carbon in these oceanic environments. Thus, thorium isotopes might be used as tracers of marine organic carbon cycling. Residence times of colloids derived from ²³⁴Th:²³⁸U disequilibria were consistently short, ranging from 1 to 14 days for COM₁₀ and from 5 to 65 days for COM₁, suggesting that marine colloids are highly reactive in marine biogeochemical processes. The discrepancy between apparent turnover times of colloids (1 kDa) derived from Th scavenging and ¹⁴C measurements suggest that ²³⁴Th and ¹⁴C may trace different geochemical pathways of colloids in the ocean.     

High-accuracy determination of iron in seawater by isotope dilution multiple collector inductively coupled plasma mass spectrometry (ID-MC-ICP-MS) using nitrilotriacetic acid chelating resin for pre-concentration and matrix separation

In the present paper we describe a robust and simple method to measure dissolved iron (DFe) concentrations in seawater down to <0.1 nmol L⁻¹ level, by isotope dilution multiple collector inductively coupled plasma mass spectrometry (ID-MC-ICP-MS) using a ⁵⁴Fe spike and measuring the ⁵⁷Fe/⁵⁴Fe ratio. The method provides for a pre-concentration step (100:1) by micro-columns filled with the resin NTA Superflow of 50 mL seawater samples acidified to pH 1.9. NTA Superflow is demonstrated to quantitatively extract Fe from acidified seawater samples at this pH. Blanks are kept low (grand mean 0.045 ± 0.020 nmol L⁻¹, n = 21, 3× S.D. limit of detection per session 0.020–0.069 nmol L⁻¹ range), as no buffer is required to adjust the sample pH for optimal extraction, and no other reagents are needed than ultrapure nitric acid, 12 mM H₂O₂, and acidified (pH 1.9) ultra-high purity (UHP) water. We measured SAFe (sampling and analysis of Fe) reference seawater samples Surface-1 (0.097 ± 0.043 nmol L⁻¹) and Deep-2 (0.91 ± 0.17 nmol L⁻¹) and obtained results that were in excellent agreement with their DFe consensus values: 0.118 ± 0.028 nmol L⁻¹ (n = 7) for Surface-1 and 0.932 ± 0.059 nmol L⁻¹ (n = 9) for Deep-2. We also present a vertical DFe profile from the western Weddell Sea collected during the Ice Station Polarstern (ISPOL) ice drift experiment (ANT XXII-2, RV Polarstern) in November 2004–January 2005. The profile shows near-surface DFe concentrations of 0.6 nmol L⁻¹ and bottom water enrichment up to 23 nmol L⁻¹ DFe.     

Multielement determination of trace metals in seawater by ICP-MS with aid of down-sized chelating resin-packed minicolumn for preconcentration

The multielement determination of trace metals in seawater was carried out by inductively coupled plasma mass spectrometry (ICP-MS) with aid of a down-sized chelating resin-packed minicolumn for preconcentration. The down-sized chelating resin-packed minicolumn was constructed with two syringe filters (DISMIC 13HP and Millex-LH) and an iminodiacetate chelating resin (Chelex 100, 200-400 mesh), with which trace metals in 50 mL of original seawater sample were concentrated into 0.50 mL of 2 M nitric acid, and then 100-fold preconcentration of trace metals was achieved. Then, 0.50 mL analysis solution was subjected to the multielement determination by ICP-MS equipped with a MicroMist nebulizer for micro-sampling introduction. The preconcentration and elution parameters such as the sample-loading flow rate, the amount of 1 M ammonium acetate for elimination of matrix elements, and the amount of 2 M nitric acid for eluting trace metals were optimized to obtain good recoveries and analytical detection limits for trace metals. The analytical results for V, Mn, Co, Ni, Cu, Zn, Mo, Cd, Pb, and U in three kinds of seawater certified reference materials (CRMs; CASS-3, NASS-4, and NASS-5) agreed well with their certified values. The observed values of rare earth elements (REEs) in the above seawater CRMs were also consistent with the reference values. Therefore, the compiled reference values for the concentrations of REEs in CASS-3, NASS-4, and NASS-5 were proposed based on the observed values and reference data for REEs in these CRMs.     

Determination of iron in seawater by electrothermal atomic absorption spectrometry and atomic fluorescence spectrometry: A comparative study

Two methods available for direct determination of total Fe in seawater at low concentration level have been examined: electrothermal atomization atomic absorption spectrometry (ETAAS) and electrothermal atomization laser excited atomic fluorescence spectrometry (ETA-LEAFS). In a first part, we have optimized experimental conditions of ETAAS (electrothermal program, matrix chemical modification) for the determination of Fe in seawater by minimizing the chemical interference effects and the magnitude of the simultaneous background absorption signal. By using the best experimental conditions, a detection limit of 80 ng L⁻¹ (20 μL, 3σ) for total Fe concentration was obtained by ETAAS. Using similar experimental conditions (electrothermal program, chemical modification), we have optimized experimental conditions for the determination of Fe by LEAFS. The selected experimental conditions for ETA-LEAFS: excitation wavelength (296.69 nm), noise attenuation and adequate background correction led to a detection limit (3σ) of 3 ng L⁻¹ (i.e. 54 pM) for total Fe concentration with the use a 20 μL seawater sample. For the two methods, concentration values obtained for the analysis of Fe in a NASS-5 (0.2 μg L⁻¹) seawater sample were in good agreement with the certified values.     

Optical biosensor for the determination of BOD in seawater

An automatic sensing system was developed using an optical BOD sensing film. The sensing film consists of an organically modified silicate (ORMOSIL) film embedded with an oxygen-sensitive Ru complex. A multi-microorganisms immobilization method was developed for the BOD sensing film preparation. Three different kinds of microorganisms, Bacillus licheniformis, Dietzia maris and Marinobacter marinus from seawater, were immobilized on a polyvinyl alcohol ORMOSILs. After preconditioning, the BOD biosensor could steadily perform well up to 10 months. The linear fluctuant coefficients (R²) in the range of 0.3-40 mg L⁻¹ was 0.985 when a glucose/glutamate BOD standard was applied. The reproducible response for the BOD sensing film could be obtained within ±2.3% of the mean value in a series of 10 samples in 5.0 mg L⁻¹ BOD standard GGA solution. The effects of temperature, pH and sodium chloride concentration on the two microbial films were studied as well. The BOD sensing system was tested and applied for the BOD determination of seawater.     

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 0.70 ng for Cu for a 2 L 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‰.     

新型螯合树脂在线预富集测定海水中痕量Cd

将新型螯合树脂(XAD-H2Dz)应用于微柱现场在线采样(MFS)新技术中,实现了海水样中痕量Cd的在线原位预富集和实验室中流动注射-火焰原子吸收(FI-FAAS)系统的联机测定。采样体积为5 mL和50 mL时,检出限(3σ)分别为68和6.7 ng/L;相对标准偏差(n=7)分别为2.0%和2.6%。对国家海水微量元素标准物质GBW(E)080040和实际样品(大连老虎滩区域海水以及连云港黄海水域)中镉进行分析,均获得了满意的结果。     

Kinetic-spectrophotometric method for the determination of trace amounts of bromide in seawater

A novel simple, sensitive and rapid kinetic-spectrophotometric method is proposed for the determination of trace amounts of bromide. The method is based on its catalytic effect on the oxidation of methylene blue (MB) by hydrogen peroxide in strongly acidic solution. The oxidation reaction is activated by large amounts of chloride and can be monitored spectrophotometrically by measuring the decrease in the absorbance of MB at 746 nm. The determination of bromide is performed by a fixed-time method at the first 100 s from the initiation of the reaction. Unlike other kinetic-spectrophotometric methods for the determination of bromide, the proposed method does not require heating the solution. Bromide can be determined in the range from 80 to 960 μg l⁻¹ with the detection limit of 35 μg l⁻¹. The relative standard deviation of ten replicate determination of 480 μg l⁻¹ bromide was 1.4%. The influence of potential interfering ions was studied. The proposed method was satisfactorily applied to the determination of bromide in seawater without interfering effect from chloride ion.     

Determination of iron-porphyrin-like complexes at nanomolar levels in seawater

A new method for the non-specific determination of iron-porphyrin-like complexes in natural waters has been developed. It is based on the chemiluminescent oxidation of the luminol in the presence of dioxygen (O₂) at pH 13. The method has been implemented in a FIA manifold that allowed the direct injection of seawater. The limit of detection is 0.11 nM of equivalent hemin (Fe-protoporphyrin IX). Fe²⁺, Fe³⁺, H₂O₂, siderophore (deferoxamin mesylate), humic acid and phytic acid did not interfere when they were present at the concentrations expected in seawater. Metal free porphyrin and Mg, Cu, Co porphyrin complexes did not induce a significant chemiluminescent signal. Poisoned unfiltered samples could be stored for several weeks before analyses. The new method was successfully applied to the determination of the Fe-porphyrin complexes contained in cultured phytoplankton and in natural samples.     

Preparation and certification of a reference material for the determination of nutrients in seawater

There is an urgent need for natural water reference materials certified for nutrients. In 1996, NRC collected seawater for a proposed CRM at a depth of 200 m in the North Atlantic; this was immediately filtered through 0.05-m cartridge filters into 50-L carboys. The water was later homogenized in the NRC laboratories in Ottawa and stabilized via gamma irradiation. Over six years of stability testing no significant deterioration was detected. In addition to the usual customary standard colorimetric procedures, alternative analytical methods were developed to enable the certification process. The production of a CRM called MOOS-1 will be discussed. Certified values, with uncertainty components addressing the homogeneity, stability, and characterization of the material, were calculated to be: orthophosphate=1.56±0.07 µmol L^–1, silicate=26.0±1.0 µmol L^–1, nitrite=3.06±0.15 µmol L^–1, and nitrite and nitrate=23.7±0.9 µmol L^–1.     

A column system for the selective extraction of U(VI) and Th(IV) using a new chelating sorbent

A new method has been developed using (bis-3,4-dihydroxy benzyl)p-phenylene diamine functionalized to XAD-16 (a polystyrene divinyl benzene copolymer) matrix, to preconcentrate mainly U(VI) and Th(IV) from synthetic and real samples. The developed method is free from matrix interference due to alkali and alkaline metal ions and preconcentrates the actinides with a high degree of selectivity, with consistent trace recoveries. The new chelating resin provides dramatic improvement in metal exchange rate, with half value saturation time (t_1/2) of less than 1.6 min. The developed method was superior in its metal loading capacity for U(VI) and Th(IV), with values of 0.666 and 0.664 mmol g⁻¹, respectively. Various physio-chemical properties like effect of solution pH, kinetic studies, resin loading capacity, sample breakthrough volume, matrix effects etc., on metal ion sorption to sorbent phase, were studied using both batch and column method. The new chelatogen was applied to extract U(VI) from near neutral real water samples. Preconcentration and separation of metal ions were possible through pH variation and also by varying the eluant concentration. A high preconcentration factor value of 350 with a lower limit of detection of 20 and 30 ng cm⁻³ was obtained for U(VI) and Th(IV), respectively. The practical applicability of the developed resin was examined using synthetic and real samples such as sea/well water samples. The method provides low relative standard deviation values of <3.5% for all analytical measurements, reflecting on the reproducibility and accuracy of the developed method. The new resin is quite durable with recycling time >35 cycles, without any major change in its quantitative metal uptake nature.     

螯合树脂浓缩柱预富集低压离子色谱分光光度法测定海水中痕量铅

采用螯合树脂浓缩柱预富集低压离子色谱分光光度法测定海水中痕量的铅。对于2.0μg/L的Pb2 溶液,测定的相对标准偏差为2.9%(n=8);将该法应用于不同盐度海水中铅的测定,获得满意结果,标准加标回收率在94%~101%之间,该法可以识别Ⅰ类海水,可以测定Ⅱ~Ⅳ类海水。     

Rapid determination of bromide in seawater samples by capillary ion chromatography using monolithic silica columns modified with cetyltrimethylammonium ion

Monolithic silica capillary columns dynamically modified with quaternary ammonium ions were evaluated for the determination of bromide in seawater samples. A quaternary ammonium ion such as cetyltrimethylammonium ion was dynamically introduced onto monolithic silica surfaces. The first layer of the modifier was introduced by electrostatic interaction, whereas the second layer was introduced by hydrophobic interaction. The latter layer worked as the anion-exchange sites. The modified monolithic silica capillary columns could be used for rapid separation of inorganic anions. Separation of authentic mixture of five anions was achieved within a few minutes. The addition of small amount of the modifier in the eluent improved the repeatability of the retention time. Seawater samples could be directly injected onto the prepared capillary columns, and bromide could be determined to be 63 mg/L.     

Precise determination of lithium isotopes in seawater using MC-ICP-MS

Li (lithium) isotope analysis using MC-ICP-MS is a very powerful tracer measurement method. This is widely used for identification of Li isotopes in many fields of study. This useful method, however, has an effect on the natural Li isotope background. This is impacted by the instrument matrix. In this study, we show that the MC-ICP-MS condition is characterized by both a low baseline background and a high-sensitivity distance at Ar plasma condition. In addition, the Li isotope ratio was measured by the use of experimental conditions that were superior to both the general plasma condition and those used in other studies. The samples were subjected to both acid leaching and a cation exchange resin (Bio-Rad AG 50 W-X8 200–400 mesh) modified for seawater samples. The isotope variations were corrected using the bracket method, the measured Li isotope ratio of sample, and the mean ratios of the L-SVEC standard (NIST L-SVEC Li₂CO₃) measured before and after the sample run. The isotope variation was presented as the deviation (per mil) of the measured ratio from that of the recommended value.     

Application of Fenton reaction for nanomolar determination of hydrogen peroxide in seawater

A simple and sensitive method for the determination of nanomolar levels of hydrogen peroxide (H₂O₂) in seawater has been developed and validated. This method is based on the reduction of H₂O₂ by ferrous iron in acid solution to yield hydroxyl radical (OH) which reacts with benzene to produce phenol. Phenol is separated from the reaction mixture by reversed phase high performance liquid chromatography and its fluorescence intensity signals were measured at excitation and emission of 270 and 298 nm, respectively. Under optimum conditions, the calibration curve exhibited linearity in the range of (0-50) × 10³ nmol L⁻¹ H₂O₂. The relative standard deviations for five replicate measurements of 500 and 50 nmol L⁻¹ H₂O₂ are 1.9 and 2.4%, respectively. The detection limit for H₂O₂, defined as three times the standard deviation of the lowest standard solution (5 nmol L⁻¹ H₂O₂) in seawater is 4 nmol L⁻¹. Interference of nitrite ion (NO₂⁻) on the fluorescence intensity of phenol was also investigated. The result indicated that the addition of 10 μmol L⁻¹ NO₂⁻ to seawater samples showed no significant interference, although, the addition of 50 μmol L⁻¹ NO₂⁻ to the seawater samples decreases the fluorescence intensity signals of phenol by almost 40%. Intercomparison of this method with well-accepted (p-hydroxyphenyl) acetic acid (POHPAA)-FIA method shows excellent agreement. The proposed method has been applied on-board analysis of H₂O₂ in Seto Inland seawater samples.