Determination of copper complexation with natural organic ligands in seawater by equilibration with MnO2 II. Experimental procedures and application to surface seawater

The MnO₂ adsorption method combined with voltammetry is proposed for the direct determination of metal complexation in seawater of various salinities as a more satisfactory alternative to direct voltammetric measurements and bioassay methods. A small quantity of MnO₂ is equilibrated with copper ions in filtered seawater. Natural organic ligands in the seawater compete for copper with the MnO₂. Total dissolved copper is measured by differential pulse anodic stripping voltammetry after filtration and acidification of the sample. Preconcentration of natural water samples is unnecessary and measurement is performed at the natural equilibrium pH of the aerated sample. The analytical limit of detection of the method depends on contamination from the filtration step, and for copper complexation a ligand concentration of 5 × 10^?8 M was obtained. The sensitivity can be increased by use of radioisotopes as tracers. The method is very versatile in that complexation of various metals may be determined by any analytical method that measures total dissolved metal concentrations. Neither organic ligands nor their complexes with copper adsorb on the MnO₂ at pH8, but at pH 1.8 MnO₂ is an efficient scavenger for electroactive organic material.Samples of surface water from the Irish Sea and the Atlantic Ocean were found to contain ligand concentrations of 1.7 × 10^?7 and 1.1 × 10^?7 M, with conditional stability constants (log values) of 9.84 ± 0.13 and 9.86 ± 0.23, respectively, at pH 8.0.     

Determination of the complexing capacity and conditional stability constants of complexes of copper(II) with natural organic ligands in seawater by cathodic stripping voltammetry of copper-catechol complex ions

A new method is proposed for the determination of complexing capacities and conditional stability constants for complexes of copper(II) with dissolved organic ligands in seawater. This method is based on ligand competition by the added ligand catechol for free metal ions. The concentration of copper-catechol complex ions is measured with great sensitivity by cathodic stripping voltammetry. The concentration of the free copper ion is calculated from the concentration of copper-catechol complex ions. Ligand concentrations and conditional stability constants are obtained from a titration of the ligands with copper. Two techniques for treatment of the data are compared. A seawater sample, originating from open oceanic conditions, is analysed and two complexing ligands were detected, having concentrations of 1.1 × 10^?8 and 3.3 × 10^?8 M, and conditional stability constants (log K′_CuL) of 12.2 and 10.2, respectively.     

RESEARCH ON THE DETERMINATION OF Pb, Cd, Cu AND Zn IN SEAWATER BY STRIPPING VOLTAMMETRY

In this paper, a comparison viral made between the two results of determining Pb, Cd, Cu and Zn in seawater by direct current (tripping voltammetry (DCS) with rotating glass carbon electrode and by differential pulse stripping voltammetry (DPS) with hanging mercury drop electrode (HMDE). By DCS, the range of linear calibration curves obtained was 4×10-3 M-2×10-7M for Cu, Zn and Cd, and 4× 10-9M-2×10-3M for Pb. By using DPS, the range of linear calibration curve was as follows: Cu 0.65-1.9 ppb; Pb 1.0-10 ppb; Zn 0.65-2.0 ppb; Cd 0.02-0.14 ppb. It was found that DCS could be used for determining Pb, Cu, Zn in coastal waters, but it is necessary to add gallium ion to it to eliminate the interference of Cu-Zn inter-metallic compound for determining Zn. The DPS is better for determinig Cd.     

DIRECT DETERMINATION OP TRACE CADMIUM IN SEAWATER BY DERIVATIVE-VOLTAMMETRY

An analytical method is proposed for the direct determination of Cd in seawater by differential pulse anodic stripping voltammetry and the derivative technique with a hanging mercury drop electrode. The process of determination is quick, simple and convenient. The concentration of Cd in seawater is only determined by adjusting the acidity of seawater to pH 2 and by taking three minutes' plating time. Sensitivity of the method is about 1×10-10M, and accuracy of that satisfactory. Relative standard deviation is about 12% when the concentration of Cd in seawater is approximately 0.04 ppb. A good agreement was obtained by a standard curve and a standard addition technique respectively from determining Cd in the same seawater. Actual measurement time per sample is about 10 min.     

Determination of the zinc complexing capacity in seawater by cathodic stripping voltammetry of zinc—APDC complex ions

A novel technique to determine complexing capacities for zinc is presented. The free zinc concentration is determined by cathodic stripping voltammetry preceded by adsorptive collection of complexes of zinc with ammonium pyrrolidine dithiocarbamate (APDC). The reduction peak of zinc is depressed as a result of ligand competition by natural organic material in the sample. Sufficient time is allowed to reach equilibrium between this material and added APDC, and equilibrium is maintained during the measurement. Both electrochemically reversible and irreversible complexes can therefore be investigated. Values for K_ZnAPDC^′ are calibrated against NTA and EDTA in seawater of several salinities; log K_ZnAPDC^′ was found to be 4.40 at 36‰, 4.36 at 24‰, 4.43 at 12‰, and 4.87 at 2.3‰. The ligand concentration and conditional stability constant, K_ZnL^′, for complexing ligands in a sample from the Irish Sea were determined in the presence of 4 × 10^?5 M APDC and with added zinc concentrations between 5 × 10^?9 and 3 × 10^?7 M. The data best fitted a complexation model containing two ligands with concentrations of 2.6 and 6.2 and 10^?8 M, and with values for log K_ZnL^′ of 8.4 and 7.5, respectively. These results are comparable to those obtained with other equilibrium techniques, but the values of the constants are greater than those from ASV measurements.     

A comparison of two voltammetric techniques for determining zinc speciation in Northeast Pacific Ocean waters

Two independent voltammetric techniques, differential pulse cathodic stripping voltammetry (DPCSV) and differential pulse anodic stripping voltammetry (DPASV), determined that 95% of the dissolved zinc is organically complexed at two depths (60 and 150 m) within the surface euphotic zone at an open ocean station in the Northeast Pacific. Average values for the concentrations of the natural zinc-complexing organic ligands (C_L) obtained from duplicate determinations at these two depths by DPCSV versus DPASV are in excellent agreement: 1.60 ± 0.01 versus 1.76 ± 0.03 nM at 60 m, and 2.14 (n=1) versus 2.22 ± 0.06 nM at 150 m. Average values for the conditional stability constants (with respect to free Zn²⁺) of the natural zinc-organic complexes (log K^′_ZnL) from duplicate determinations at both depths by DPCSV versus DPASV are 10.3 ± 0.2 versus 11.2 ± 0.2. Additional research is required to assess the significance of the difference in the conditional stability constants determined by these two techniques. These results confirm recent observations that strong zinc complexes formed with an organic ligand class existing at nanomolar concentrations dominates zinc speciation in the North Pacific.     

The determination of sulfide in seawater by flow-analysis with voltammetric detection

Preliminary measurements of sulfide in seawater using cathodic stripping voltammetry and a hanging mercury drop electrode (HMDE) in batch-mode showed that the sulfide peak decreased rapidly with time. This decrease was not caused by O₂, H₂O₂ or IO₃⁻, and the sulfide peak was not stabilised by trace metal additions. A home-made flow-cell was constructed to enable the determination of sulfide in seawater using voltammetry with an HMDE. A stable sulfide peak was obtained by flow-analysis with voltammetric detection, with a precision of 2.8% and detection limit of 0.5 nM at a 60 s adsorption time. Several thiol compounds were found to produce a peak at, or very close to, the peak potential for sulfide. Their interference was evaluated by allowing the sulfide peak in conventional (batch) voltammetry to decay. Comparative experiments showed that waste metallic mercury is responsible for removal of sulfide in batch-mode analysis due to formation of insoluble mercuric sulfide salts causing the rapid decay of the sulfide peak. The problem is circumvented by using flow-analysis to determine sulfide.     

Cu complexation by organic ligands in the sub-arctic NW Pacific and Bering Sea

Cu speciation was characterized at three stations in the sub arctic NW Pacific and Bering Sea using cathodic stripping voltammetry with the competing ligands benzoylacetone and salicylaldoxime. A single ligand model was fit to the titration data, yielding concentrations throughout the water column of ∼3–4 nM, and conditional stability constants ranging from 10^12.7 to 10^14.1, this range being partly due to the choice of competing ligand. Free Cu²⁺ in surface waters was 2–4×10⁻¹⁴ M, in close agreement with values reported by previous workers in the NE Pacific using anodic stripping voltammetry (ASV). However, those results showed that complexation by strong organic ligands becomes unimportant below 200–300 m, while our data indicated Cu is strongly complexed to depths as great as 3000 m. Free Cu²⁺ concentrations in surface waters reported here and in previous work are close to the threshold value where Cu can limit the acquisition of Fe by phytoplankton.     

Zinc speciation in the Northeastern Atlantic Ocean

Measurements of zinc and zinc complexation by natural organic ligands in the northeastern part of the Atlantic Ocean were made using cathodic stripping voltammetry with ligand competition. Total zinc concentrations ranged from 0.3 nM in surface waters to 2 nM at 2000 m for open-ocean waters, whilst nearer the English coast, zinc concentrations reached 1.5 nM in the upper water column. In open-ocean waters zinc speciation was dominated by complexation to a natural organic ligand with conditional stability constant (log K_ZnL′) ranging between 10.0 and 10.5 and with ligand concentrations ranging between 0.4 and 2.5 nM. The ligand was found to be uniformly distributed throughout the water column even though zinc concentrations increased with depth. Organic ligand concentrations measured in this study are similar to those published for the North Pacific. However the log K_ZnL′ values for the North Atlantic are almost and order of magnitude lower than those reported by Bruland [Bruland, K.W., 1989. Complexation of zinc by natural organic-ligands in the central North Pacific. Limnol. Oceanogr., 34, 269–285.] using anodic stripping voltammetry for the North Pacific. Free zinc ion concentrations were low in open-ocean waters (6–20 pM) but are not low enough to limit growth of a typical oceanic species of phytoplankton.     

阳极溶出伏安法测定海水中低浓度镉

镉能积累于人体及生物体内造成慢性中毒,引起严重的“骨头病”[1],并与严重的心血管病有连带关系[2].海洋中镉的污染问题已引起人们极大的重视.目前,我国与世界其他国家一样,已将镉的污染列为国家海洋环境重点监测项目之一.     

On the sulphur chemistry of a super-anoxic fjord, Framvaren, South Norway

The concentrations of total carbonate (C_t), sulphate, sulphide, thiols and oxygen, the ratio between the stable sulphur isotopes ³⁴S and ³²S in sulphate and sulphide, and the density (used to calculate salinity) were determined on samples from the water column of Framvaren, a superanoxic fjord in southern Norway. From a depth of 18m (the oxic-anoxic boundary) the initial sulphate concentration, ([SO₄]_init), as calculated from salinity, is significantly higher than the sum of the measured sulphur species. This is attributed to a loss of sulphur from the water column. The amount of total carbonate produced, corrected for the initial concentration (C_t - 2.4 Sal/35) is found to be proportional to the amount of sulphate consumed, ([SO₄]_init - [SO₄]), according to the following relation C_t- 2.4 Sal/35 = 1.84 ([SO₄]_init - [SO₄]). Isotopic fractionation caused by bacterial sulphate reduction in the anoxic part of the water column produces sulphide with a δ³⁴S 40‰ lower than the δ³⁴S for sulphate at corresponding depths. The isotopic fractionation also results in δ³⁴S value for the remaining sulphate at depths below 80 m being considerably higher than the mean value for ocean water, which is close to + 20‰. The δ³⁴S values for sulphate at depths between 10 and 50 m were lower than + 20‰ which indicates oxidation of sulphide, which follows upon diffusion of sulphide from deeper parts of the water column and inflow of oxygenated seawater over the sill into the anoxic water of the fjord. A conclusive scenario of the Framvaren sulphur chemistry is presented.     

Using the acoustic-pulse conservation law in estimating the energy of surface acoustic sources by remote sounding

The atmospheric effect on the characteristics of infrasonic signals from explosions has been studied. New methods have been proposed to remotely estimate the energy of explosions using the data of infrasonic wave registration. One method is based on the law of conservation of acoustic pulse I, which is equal to the product of the wave profile area S/2 of the studied infrasonic signal and the distance to the source E_I [kt] = 1.38 × 10^–10 (I [kg/s])^1.482. The second method is based on the relationship between the explosion energy and the dominant period T of the recorded signal, EТ [kt] =1.02 × (Т [s]²/σ)^3/2, where σ is a dimensionless distance used for determining the degree of manifestation of nonlinear effects in the propagation of sound along ray trajectories. When compared to the conventional E_W (Whitaker’s) relation, the advantage of the EI relation is that it can be used for pulsed sources located at an arbitrary height over the land surface and having an arbitrary form of the initial-pulse profile and for any type of infrasonic arrivals. A distinctive feature of the expression for E_Т is that the atmospheric effect on the characteristics of recorded infrasonic signals is explicitly taken into account. These methods have been tested using infrasonic data recorded at a distance of 322 km from the sources (30 explosions caused by a fire that occurred at the Pugachevo armory in Udmurtia on June 2, 2011). For the same explosion, empirical relations have been found between energy values obtained by different methods: E_I = 1.107 × E _W , E _Т = 2.201 × E _I .     

DETEMINATION OF TUNGSTEN AND MOLYBDENUM IN SEAWATER

Tungsten and molybdenum in seawater can be sensitively and accurately determined by the polaro-graphic catalytic wave. In a supporting electrolyte containing HCl-benzilic acid-Nad, tungsten has a clear and stable catalytic wave. Then, the peak current of molybdenum increases as KClO3 is added into the above medium. The sensitivity of the proposed method is 5×10-2 M for W and 6×10-10 M for Mo, respectively.This method is an extremely quick, sensitive one and is suitable for the analysis of various kinds of water.     

Methane hydrate dissolution rates in undersaturated seawater under controlled hydrodynamic forcing

The dissolution of in-situ generated methane hydrate in undersaturated, synthetic seawater (S = 35) was investigated in a series of laboratory-based experiments at P-/T-conditions within the hydrate stability field. A controlled flow field was generated across the smooth hydrate surface to test if, in addition to thermodynamic variables, the dissolution rate is influenced by changing hydrodynamic conditions. The dissolution rate was found to be strongly dependent on the friction velocity, showing that hydrate dissolution in undersaturated seawater is a diffusion-controlled process. The experimental data was used to obtain diffusional mass transfer coefficients k_d, which were found to correlate linearly with the friction velocity, u. The resulting k_d/u-correlation allows predicting the flux of methane from natural gas hydrate exposures at the sediment/seawater interface into the bulk water for a variety of natural P, T and flow conditions. It also is a tool for estimating the rate of hydrate regrowth at locations where natural hydrate outcrops at the seafloor persist in contact with undersaturated seawater.     

琼东海域今生颗石藻群落研究

通过2012年7、8月在南海北部陆架琼东上升流区域的水文、化学和生物的现场综合采样调查,对采集过滤的今生颗石藻膜样在偏振光显微镜下鉴种并统计细胞丰度,分析了夏季该海域的颗石藻群落结构特征及分布规律。结果表明,夏季琼东上升流区共检出今生颗石藻34种,优势物种有赫氏艾密里藻(Emiliania huxleyi)、大洋桥石藻(Gephyrocapsa oceanica)、纤细伞球藻(Umbellosphaera tenuis)、卡特螺旋球藻(Helicosphaera carteri)、地中海花冠球藻(Coronosphaera mediterranea)等,颗石粒细胞丰度介于0~2 040.23×103粒/L,平均值8.10×103粒/L,颗石球丰度介于0~68.90×103cells/L,平均值5.01×103 cells/L。大多数颗石藻集中分布在上升流信号强的水体中。琼东中部水域的生物多样性指数H′较雷州半岛以东水域高,颗石粒群落的均匀度指数J分布与H′呈镶嵌模式。聚类Cluster和多维定标MDS结果,将颗石粒和颗石球群落各分成4个和5个组群,经相似性分析(ANOSIM)检验证明此种划分是显著的。将生物与海区环境因子进行冗余分析(Redundancy analysis,RDA)结果表明,N/P、PO3-4、NO-2和SiO2-3是影响本次调查的今生颗石藻生物群落的主控因子。     

棉兰老流和棉兰老潜流在季节尺度上的关系研究

The ocean general circulation model for the earth simulator(OFES) products is applied to estimate the transports of the Mindanao Current(MC) and the Mindanao undercurrent(MUC) and explore the relation between them on seasonal scale. In general, the MUC is composed of the lower part of the Southern Pacific Tropical Water(SPTW)and Antarctic Intermediate Water(AAIW). While the deep northward core below 1 500 m is regarded as a portion of MUC. Both salinity and potential density restrictions become more reasonable to estimate the transports of MC/MUC as the properties of water mass having been taken into consideration. The climatological annual mean transport of MC is(37.4±5.81)×10~6 m~3/s while that of MUC is(23.92±6.47)×10~6 m~3/s integrated between 26.5 σ_θ and 27.7 σ_θ, and(17.53±5.45)×10~6 m~3/s integrated between 26.5 σ_θ and 27.5 σ_θ in the OFES. The variations of MC and MUC have good positive correlation with each other on the seasonal scale: The MC is stronger in spring and weaker in fall, which corresponds well with the MUC, and the correlation coefficient of them is 0.67 in the OFES.The same variations are also appeared in hybrid coordinate ocean model(HYCOM) results. Two sensitive experiments based on HYCOM are conducted to explore the relation between MC and MUC. The MUC(26.5σ_θ27.7) is strengthening as the MC increases with the enhancement of zonal wind field. It is shown,however, that the main part of the increasement is the deeper northward high potential density water(HPDW),while the AAIW almost remains stable, SPTW decreases, and vice versa.     

Virio- and bacterioplankton in the estuary zone of the Ob River and adjacent regions of the Kara Sea shelf

The distribution of structural and functional characteristics of virioplankton in the north of the Ob River estuary and the adjacent Kara Sea shelf (between latitudes 71°44′44″ N and 73°45′24″ N) was studied with consideration of the spatial variations in the number (N _B) and productivity (P _B) of bacteria and water properties (temperature, salinity, density) by analyzing samples taken in September 2013. The number of plankton viruses (N _V), the occurrence of visible infected bacteria cells, virus-induced mortality of bacteria, and virioplankton production in the studied region varied within (214?2917) × 10³ particles/mL, 0.3?5.6% of NB, 2.2?64.4% of P _B, and (6?17248) × 10³ particles/(mL day), respectively. These parameters were the highest in water layers with a temperature of +7.3–7.5°C, salinity of 3.75?5.41 psu, and conventional density (στ) of 2.846?4.144. The number of bacterioplankton was (614?822) × 10³ cells/mL, and the N _V/N _B ratio was 1.1?4.5. A large amount of virus particles were attached to bacterial cells and suspended matter. The data testify to the considerable role of viruses in controlling the number and production of heterotrophic bacterioplankton in the interaction zone of river and sea waters.     

Contents of strontinm-90 and ruthenium-106 in beach and shallow water deposits of noto peninsula

⁹⁰Sr,¹⁰⁶Ru, natural strontium and major elements were studied in 12 samples of beach deposits from Togi, Fukuura and Shiga, and in 26 samples of shallow water sediments from sea off Fukuura, Noto Peninsula, Ishikawa Pref., Japan.The average contents of natural strontium and⁹⁰Sr in the beach deposits were 488 ppm ranging from 247 to 1,550 ppm and 45±9 pCi kg^–1-dry mud ranging from 18 to 72 pCi kg^–1-dry mud, respectively. While the average contents of natural strontium,⁹⁰Sr and¹⁰⁶Ru in the sediments were 234 ppm ranging from 136 to 415 ppm, 22±6 pCi kg^–1-dry sand ranging from 7 to 48 pCi kg^–1-dry sand and 0.6 ±0.2 nCi kg^–1-dry ranging from 0.3 to 1.2 nCi kg^–1-dry, respectively.The average contents of each natural strontium and⁹⁰Sr in the beach deposits were about two times higher than those in the shallow water sediments. But no obvious relation of natural strontium to⁹⁰Sr was found in all the samples. The enrichment of⁹⁰Sr and¹⁰⁸Ru in the beach deposits or tthe sediments were as high as 150320 and of 2,0003,000 compared with average contents of⁹⁰Sr and¹⁰⁶Ru in a liter of surface water from the Japan Sea. It is to be noticed that the average¹⁰⁶Ru to⁹⁰Sr ratio of 27 for the shallow water sediments is much higher than the average of 1.0 for surface sea water of the Japan Sea.As to major elements of the samples, the beach deposits are rich in silicon (Av. 70.89 ±0.92% SiO₂), but poor in iron (Av. 2.99±0.32% Fe₂O₃). Whereas the shallow water sediments are poor in silicon (Av. 52.96±10.33% SiO₂) and rich in iron (Av. 5.50±1.90% Fe₂O₃), calcium (Av. 9.64±9.22% CaO) and magnesium (Av. 2.83±1.58% MgO).     

锑原位掺杂SiO2@PDA-Sb复合材料修饰电极用于海水中Zn离子检测

本研究提出了一种用于检测海水中锌离子(Zn²⁺)含量的电化学检测方法。该方法首先应用水热法合成SiO₂@PDA-Sb复合材料,然后将该复合材料修饰到玻碳电极上制备SiO₂@PDA-Sb-Nafion/GCE,利用差分脉冲阳极溶出伏安法(DPASV)对珠江口海水水样中Zn²⁺进行测定。研究结果表明,Zn²⁺在SiO₂@PDA-Sb-Nafion/GCE上具有较强的溶出峰。在最优条件下,SiO₂@PDA-Sb-Nafion/GCE对Zn²⁺浓度在1～1 000 nmol/L范围内可实现灵敏、准确的检测,Zn²⁺的检测出限为0.71 nmol/L。加标回收率实验显示Zn²⁺加标回收率为93.19%～100.12%,表明该方法可应用于现场海水样品Zn²⁺测定。本方法具有电极制作简单、稳定性和抗干扰性良好,能够提高现有测定方法的检测限和精确度,在现场海水检测...