Screening of dissolved heavy metals (Cu,Zn, Mn,Al, Cd,Ni, Pb) in seawater by a liquid-membrane–ICP–MS approach

A bulk liquid membrane system has been developed and applied to the simultaneous separation and preconcentration of up to seven heavy metals (copper, zinc, lead, cadmium, aluminium, manganese, and nickel) in seawater. Copper was selected to optimize transport conditions and then, under these conditions, the simultaneous extraction of other heavy metals was studied. The system achieved preconcentration yields ranging between 44.11% (Cd) and 77.77% (Cu) after nine hours of operation, the effectiveness of metal transport being Cu > Zn > Pb > Mn > Ni > Al > Cd. The system was applied to the preconcentration of four real seawater samples before their quantification by inductively coupled plasma–mass spectrometry (ICP–MS). Compared with the analytical procedures commonly used for trace metal determination in oceanography, the results obtained demonstrated that the new system may be used as a very clean (sample contamination-free), simple, and one-step alternative for semiquantitative, and even quantitative, simultaneous determination of heavy metals in seawater.     

Determination of trace levels of aquaculture chemotherapeutants in seawater samples by SPME-GC-MS/MS

A sensitive and efficient solid-phase microextraction (SPME) method for the determination of organophosphorous (OPPs) and pyrethroid pesticides (Pyrs) in aquaculture-seawater samples by using GC with MS/MS (GC-MS/MS) was developed. Dichlorvos and chlorpyrifos (OPPs); permethrin, alpha-cypermethrin and deltamethrin (Pyrs) were selected according to their use as chemotherapeutants in the aquaculture industry. Different parameters affecting extraction efficiency such as fibre coating, agitation, pH and extraction time profiles were investigated. An experimental central composite design (alpha = 1) and desirability functions were used for the simultaneous optimization of extraction temperature and sample volume. Finally, a method based on direct SPME in 40 min at 75 degrees C using 100-microm-thick poly(dimethyl)siloxane (PDMS) fibre and 20 mL of sample volume is proposed. The method was validated, exhibiting good linearity, precision and accuracy parameters with picogram per millilitre LODs. The proposed methodology was applied to determine the ultratrace levels of OPPs and Pyrs in aquaculture-seawater samples by the standard addition approach, which proved to be reliable and sensitive, in addition to requiring only small amounts of sample.     

High-Performance Alkaline Seawater Electrolysis with Anomalous Chloride Promoted Oxygen Evolution Reaction

A highly selective and durable oxygen evolution reaction (OER) electrocatalyst is the bottleneck for direct seawater splitting because of side reactions primarily caused by chloride ions (Cl⁻). Most studies about OER catalysts in seawater focus on the repulsion of the Cl⁻ to reduce its negative effects. Herein, we demonstrate that the absorption of Cl⁻ on the specific site of a popular OER electrocatalyst, nickel-iron layered double hydroxide (NiFe LDH), does not have a significant negative impact; rather, it is beneficial for its activity and stability enhancement in natural seawater. A set of in situ characterization techniques reveals that the adsorption of Cl⁻ on the desired Fe site suppresses Fe leaching, and creates more OER-active Ni sites, improving the catalyst's long-term stability and activity simultaneously. Therefore, we achieve direct alkaline seawater electrolysis for the very first time on a commercial-scale alkaline electrolyser (AE, 120 cm² electrode area) using the NiFe LDH anode. The new alkaline seawater electrolyser exhibits a reduction in electricity consumption by 20.7 % compared to the alkaline purified water-based AE using commercial Ni catalyst, achieving excellent durability for 100 h at 200 mA cm⁻².     

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.     

吹扫捕集-气相色谱法同时测定海水中的氟氯烃和六氟化硫

氟氯烃(CFCs)和六氟化硫(SF6)都是人工合成的卤代化合物,在海洋科学考察中是非常重要的基础观测参数,在示踪海/气交换、水团交换等一系列重要海洋学过程研究中均有特殊的应用价值;同时,也可以用于估算表观耗氧速率(Apparent oxygen utilization rate,AOUR)以及人为碳(Anthropogenic C02,Cant)等一些重要的物理及生物地球化学过程参量.CFCs,SF6在海水中的浓度非常低,测量难度大,而CFCs和SF6的联合使用对海洋学过程研究具有重大意义.本研究建立了一套吹扫捕集系统以分析海水中CFC-12和SF6,对吹扫捕集系统测定条件进行了优化,最佳的实验条件为:捕集温度-70℃,吹扫时间8min,吹扫压力310 kPa,脱附时间30 s,脱附温度90℃.本方法测定简单、灵敏度高,CFC-12和SF6的检出限分别为0.02 pmol/kg和0.03 fmol/kg,CFC-12和SF6的测定精密度分别为±1.2％和±0.5％.标准工作曲线的线性相关系数均大于0.9995.本方法成功应用于2014年中国第六次北极科学考察航次中采集的海水样品的测定.     

微顺序注射-镉柱还原分光光度法测定海水中总氮

基于微顺序注射-阀上实验室,采用镉柱还原-偶氮染料染色分光光度法测定海水中总氮,对实验参数进行了优化,并进行了干扰因素实验。结果表明,海水中主要离子和盐度对本实验方法测定会产生干扰,采用一定盐度的国家标准海水作为溶剂制备系列标准溶液,可消除干扰。海水中总氮浓度在0.03~1.00 mg/L范围内与吸光度呈良好线性,线性相关系数r=0.9993;测定含氮浓度为0.2 mg/L的国家标准海水,相对标准偏差(RSD)为4.9％;方法的检出限为0.010 mg/L;样品加标回收率在99.5％~101.1％之间。经t检验分析,本方法与国标方法测定数据无显著性差异,可用于海水样品中总氮的测定。     

Simultaneous determination of suspended particulate trace metals (Co, Ni, Cu, Zn, Cd and Pb) in seawater with small volume filtration assisted by microwave digestion and flow injection inductively coupled plasma mass spectrometer

A new technique for the determination of suspended particulate trace metals (P-metals >0.2 μm), such as Co, Ni, Cu, Zn, Cd and Pb, in open ocean seawater has been developed by using microwave digestion coupled with flow injection inductively coupled plasma mass spectrometry (FI-ICP-MS). Suspended particulate matter (SPM) was collected from 500 mL of seawater on a Nuclepore filter (0.2 μm) using a closed filtration system. Both the SPM and filter were completely dissolved by microwave digestion. Reagents for the digestion were evaporated using a clean evaporation system, and the metals were redissolved in 0.8 M HNO₃. The solution was diluted with buffer solution to give pH 5.0 and the metals were determined by FI-ICP-MS using a chelating adsorbent of 8-hydroxyquinoline immobilized on fluorinated metal alkoxide glass (MAF-8HQ). The procedure blanks with a filter were found to be 0.048 ± 0.008, 10.3 ± 0.3, 0.27 ± 0.05, 3.3 ± 1.8, 0.02 ± 0.03 and 0.85 ± 0.09 ng L⁻¹ for Co, Ni, Cu, Zn, Cd and Pb, respectively (n = 14). Detection limits defined as 3 times the standard deviation of the blanks were 0.023, 0.90, 0.14, 5.3, 0.078 and 0.28 ng L⁻¹ for Co, Ni, Cu, Zn, Cd and Pb, respectively. Accuracy was evaluated using certified reference materials of chlorella (NES CRM No. 3) and marine sediment (HISS-1). The method was applied to the determination of vertical distributions for P-Co, Ni, Cu, Zn, Cd and Pb in the Western North Pacific.     

海水中硝酸盐的无阀连续流动分析

建立了一种无阀连续流动分析方法和装置,仅用一台多通道蠕动泵传送试剂和样品,无需依靠注入阀、电磁阀和定量环进行试剂或样品的选择和定量输入.样品通过铜-镉还原柱,将硝酸盐还原为亚硝酸盐,然后用重氮-偶氮光度法进行测定.研究结果表明,硝酸盐的线性范围为5 ～ 180 μmol/L,方法检出限为0.27.μmol/L,对10和80 μmol/L硝酸盐溶液连续测定11次,相对标准偏差分别为1.4％和1.3％,不同盐度的实际水样加标回收率在99.4％ ～ 106.1％之间.测定结果与流动注射分析法相比,无显著性差异.与流动注射分析相比,无阀设计装置大大降低了成本,操作更加简便,有利于在普通实验室或现场连续监测中推广使用.本方法成功应用于厦门西港海水样品中硝酸盐的测定以及九龙江河口区的硝酸盐走航式监测.     

Characterization of seawater and weather aged polyurethane elastomer for bend stiffeners

A bend stiffener grade polyurethane (PU) elastomer was physically and mechanically characterized by attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetric analysis and tensile tests. The material was then exposed to artificial seawater and weather up to 12 months to evaluate its stability as bend stiffeners are exposed to this type of environment during offshore operation. The characterization of aged samples was performed comparing the ageing effects on the chemical structure, thermal stability and mechanical properties with those of the non-aged material. The mass variation of aged samples immersed in artificial seawater was also measured. A slight change in the chemical structure led to a color change from dark green to brown in the samples exposed to natural weathering for 12 months. Increases in thermal stability, stiffness and strength characteristics were also verified, which may be associated to additional crosslink formation. In contrast, a significant mechanical property drop was observed for the artificial seawater aged PU, being attributed to a plasticizer effect induced by the ageing fluid. The stress-strain curves were adjusted with the Mooney-Rivlin model allowing the crosslink density estimation. The weather aged PU presented higher crosslink density than seawater aged and non-aged samples.     

Direct Fluorescence Monitoring of Coal Organic Matter Released in Seawater

Whenever immersed in seawater after a collier accident, a fossil fuel such as coal could become a source of pollution to the marine environment. To study the effect of such a contamination, four coal samples from different origins were used. A first analysis on those coals enabled us to determine the content of polycylic aromatic hydrocarbons. Seawater was then mixed with coal to study the organic matter released from coal into seawater. Fluorescence was used for its sensitivity to aromatic compounds, with the additional purpose of evaluating the relevance of using an immerse fluorescence probe to monitor water pollution. Excitation–emission matrices were recorded and the excitation–emission wavelength range corresponding to the highest fluorescence intensity was 230 nm/[370 nm; 420 nm]. The samples with coal happened to fluoresce more than the coal-free samples, the difference depending on the coal origin. The fluorescence intensity increased with coal mass, up to some limit. The particle size also influenced the fluorescence intensity, the finest particles releasing more fluorescing substances, due to their higher exchange surface. When seawater percolated through coal, the samples fluoresced highly at the beginning, and then the fluorescence intensity decreased and reached the seawater level. However, even with a 10 ns acquisition time shift, the fluorescence spectra were not specific enough to show the presence of PAHs in the samples, which were too diluted to be detected, whenever released from coal into seawater. The lifetimes of the seawater and of the coal samples were respectively 4.7 and 3.8 ns, indicating that the substances released from coal mainly consisted of short-lived fluorescing substances, such as natural humic or fulvic substances. Consequently, the presence of coal does not seem to be too detrimental to the marine environment, and a direct fluorescence probe could be used to monitor the seawater organic charge increase due to the immersion of coal in seawater.