Polarographic determination of orthophosphate in seawater

-In the system HCl-Sb (Ⅲ)-ammonium molybdatc-acetone-butanone, PO43-, Sb (Ⅲ) and Mo (VI) form ternary heteropoly acid. This ternary heteropoly acid anion is adsorbed on the dropping mercury electrode and reduced quickly into heteropoly blue. The process of electrochemical reaction will produce a sensitive polarographic wave with peak potential -0.42V (vs S.C.E.). The detection limit is 6×10-8 mol/1. Variable coefficients are 10% and 3% for 0.1 μmol/l and 1 μmol/1 respectively.This method is sensitive, accurate and extremely rapid for analysis of seawater.     

海水中重金属铅的检测方法研究进展

铅(Pb)是已知毒性最大的重金属污染物之一,它可通过呼吸以及饮食摄入人体.铅是一种慢性的积累性毒物和潜在的致癌、致突变物质.铅的性质与钙类似,在人体骨骼中能够积蓄,主要损害神经系统、造血器官和肾脏 [1].鉴于重金属铅对人体如此严重的生物毒性作用,美国环保总局(EPA)将其列入内分泌干扰物(又称环境激素)名单,因此对环境水体中铅的检测具有重要意义.本文简述了海水中铅的含量及其存在形态,评述了原子光谱法、分子光谱法、质谱法及电化学法在海水中铅含量及其形态分析中的应用.     

A tentative determination of methylmercury in seawater

A bioassay experiment using caged mussels has suggested a total concentration of methylmercury in the seawater of a polluted estuary of 0.06 ng dm^?3. The technique may provide a useful tool for the assessment of relative concentrations of methylmercury in seawater at different locations.     

Potentiometric determination of calcium and magnesium in seawater

Methods are described for the complexometric determination of calcium and magnesium in seawater, using an amalgamated silver electrode for end-point detection. In the presence of a small amount of mercury(II)-chelonate, the amalgamated silver electrode serves as a pM indicator during the complexometric titration, the Hg complex being stronger than Ca, Mg and Sr complexes. Calcium is determined by titration with EGTA, calcium+magnesium+strontium by titration with EDTA and magnesium is obtained by difference. Average values of 0.02120 (standard deviation 0.00004) for Ca:Cl‰ and 0.06671 (standard deviation 0.00014) for Mg:Cl‰ were obtained for samples from tropical North Atlantic Ocean.     

Studies on the determination of inorganic iodine in seawater

Existing methods for the determination of the various forms of iodine present in seawater are laborious or unwieldy in use. This paper describes modified forms of the iodate and total iodine methods described by Barkley and Thompson (1960), a spectrophotometric procedure for iodate determination derived from Johannesson's (1958) work, and an automatic method for total iodine determination. Procedures for iodate and total-iodine determination which are suitable for use aboard ship, are recommended. Both procedures for iodate determination returned a standard deviation close to 0.5 μg/l when several replicate samples of a seawater containing approximately 30 μg/l of iodate-iodine were analysed. The automatic method for total iodine determination yielded a standard deviation of 0.8 μg/l by the repeated analysis of a seawater containing a total of approximately 50 μg/l of iodine. Suitable methods for the filtration and storage of seawater are also described.     

The automatic determination of iodate- and total-iodine in seawater

The development of procedures for the determination of iodate- and total-iodine content of seawater, which use a Technicon Auto-Analyser, is described. In both procedures the appropriate iodine species is first converted to iodate-iodine. Then, this is reacted with acid and excess iodide to give the iodonium ion, I₃^?, which is detected spectrophotometrically. In the total-iodine procedure the pre-oxidation is accomplished using bromine water. In the iodate procedure a pre-oxidation step using iodine-water can be included. It is anticipated that this will be used to test for the presence of naturally occurring reducing agents in seawaters, which by their action on iodonium ions could lead to an underestimate in iodate concentration. Seawaters, particularly coastal and surface oceanic ones, are known to contain iodine-reducing substances. Therefore, the validity of results obtained through the iodometric method for iodate must remain in some doubt until these tests have been made. The use of this method on anoxic waters which contain sulphides appears to be a prime example of where caution should be observed. The iodate procedure, both with and without pre-oxidation, has been tested on approximately 50 samples of waters from the Eastern Pacific Ocean; these waters did not appear to contain significant amounts of reducing agents. In a similar study, it was found that there was no significant difference between the results obtained by the new total-iodine procedure and an earlier automatic catalytic one.     

Silicate correction in the colorimetric determination of phosphate in seawater

An improved Strickland and Parsons' method, in which silicate correction is made, is described for the colorimetric determination of phosphate in seawater. Silicate correction is made by subtracting the value of 0.025 (C/100)², whereC is silicate concentration (µg atoms 1^?1), from the observed phosphate concentration. The relative standard deviations are 2 % at the 1 µg atom PO ₄ ^3? ?Pl^?1 level and less than 1 % at the 3 µg atoms PO ₄ ^3? ?Pl^?1 level in seawater.     

An improved method for the determination of ammonia in seawater

The Liddicoat, Tibbitts and Butler method for the determination of ammonia in seawater has been noticeably improved by replacing the UV lamp with a 300 VA tungsten lamp. The characteristics so achieved, a low blank value (0.012 ± 0.002a.u.), a good molar absorptivity (23.90 × 10⁻³) and a reasonably short reaction time (1 h), are such that this modified procedure is more convenient for routine work in chemical oceanography.     

红树植物中铝的示波极谱滴定

锌在示波极谱图上具有敏锐的切口,在pH为2～3的HCl-NaCl介质中,可用EDTA直接滴定铝。当滴加EDTA至切口消失时,即达到滴定终点。对红树植物体中铝的分析结果表明:此方法具有直观、操作简便、分析快速的优点,回收率相对误差在10%左右。几种红树体的不同部分铝的质量分数(干重计)分别是:叶为(6.69～29.9)×10~(-3),树干为(1.91～26.8)×10~(-3),常年生树枝为(5.54～29.8)×10~(-3).     

海水中低含量铵氮的高灵敏度荧光法测定

提出了一种改进的、可测定海水中低含量铵氮的高灵敏度荧光分析方法。其原理是在硼酸缓冲溶液的作用下,海水中的铵氮与邻苯二甲醛(OPA)发生衍生化反应,通过测定生成的荧光产物来确定水体中铵氮的浓度。方法的检测限极低(0.002 5μmol/L),重现性好,且水样用量少(10 mL),适用于海水中溶解有机物的光铵化研究及其他低铵含量水样的测定。     

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.     

ICP-OES标准加入法准确测定海水中的硼

硼作为海水中的重要组分,其准确测定对海洋环境生物地球化学过程研究具有重要意义。海水中硼的常用测定方法具有前处理步骤繁琐、耗时长、样品易被污染、灵敏度低等缺点,不适于大批量海水样品的准确测定。为剔除海水高盐基体效应及干扰,本文运用电感耦合等离子体发射光谱法(ICP-OES),将海水样品进行稀释,采用标准加入法建立工作曲线,对海水中硼含量进行准确测定。正交实验显示,ICP-OES最佳工作条件为射频功率1400 W,雾化气流量0.7 L/min,观测高度14 mm,进样泵速1.5 m L/min。标准加入法标准曲线相关系数大于0.999,相对标准偏差为0.76%~1.27%,加标回收率为94.6%~101.8%,方法检出限为1.073μg/L。实际的海水样品分析表明,该方法可消除海水基体干扰,减少测定误差,并且前处理操作简单快速,化学试剂用量少,回收率高,精密度好,灵敏度高,可用于海水及其它高盐样品中硼含量的准确测定。     

Automatic determination of dissolved organic carbon in seawater in the sub-ppm range

The improvement of a dissolved organic carbon (DOC) analysis technique is described. This continuous flow system, based on both persulfate and UV oxidations, allows the automatic determination of DOC in sea and estuarine waters. The use of FID detection gives a very high sensitivity, permitting the detection of small variations in carbon content. The efficiency of the method and its sensitivity are tested, together with the influence of initial pH and duration of nitrogen bubbling. The system can also be used to determine total or inorganic carbon.     

The determination of phosphonates in seawater by fractionation of the total phosphorus

A method is presented for the determination of phosphonates dissolved in seawater, which takes advantage of their chemically strong carbon-phosphorus bond resistant to phosphatase action and acid hydrolysis. One aliquot (A) of the seawater sample is submitted to phosphatase treatment followed by strong acid hydrolysis, while another aliquot (B) is submitted to total phosphorus determination by nitrate oxidation capable of breaking down phosphonates as well as phosphate esters, nucleotides and polyphosphates. The difference between the molybdate-reactive phosphate obtained from (A) and (B) gives a reasonably accurate measure of the phosphonates present in the seawater sample.     

The effect of nitrite on the spectrophotometric determination of iodate in seawater

A widely used method for determining iodate in seawater involves reaction of the IO₃^? with excess I^?, under acid conditions, to form I₂ which is measured colorimetrically. It is known that when the acidification is by mineral acid, nitrite can interfere with the method by oxidising I^? to I₂ in an analogous way to IO₃^?. Some workers have used sulphamic acid for acidification since it is reported to destroy nitrite in solution.We have investigated the extent of nitrite interference in the colorimetric determination of iodate using both mineral acid and sulphamic acid for acidifying the reaction mixture. In seawater the extent of the interference is equivalent to 0.212 μM 1^?1 IO₃^? per μM 1^?1 NO₂^? with sulphuric acid, and 0.128 μM 1^?1 IO₃^? per μM 1^?1 NO₂^? with sulphamic acid. This means that for a seawater containing 0.31 μM 1^?1 (39 μg 1^?1) IO₃^?, the presence of 0.5 μM 1^?1 NO₂^? will lead to an error of 25% in the iodate determined colorimetrically in methods using sulphuric acid, and 15% in methods in which sulphamic acid is used.     

Colorimetric determination of nanomolar concentrations of ammonium in seawater using solvent extraction

A solvent extraction method for measuring nanomolar concentrations of ammonium in seawater is described. The procedure is based on formation of indophenol in alkaline solution by reaction of phenol, hypochlorite and ammonia using sodium aquopentacyanoferrate as a coupling agent. Indophenol is then concentrated by extraction into n-hexanol at low pH and re-extraction into aqueous alkaline buffer. The concentration of indophenol blue is determined colorimetrically. The molar absorbance is 2.08 × 10⁵ absorbance units per molar NH₄⁺ in seawater with a precision of ± 1.9 nM NH₄⁺ (95% Cl) for concentrations ≤ 50 nanomolar. This represents a 12-fold improvement in sensitivity and a 26-fold improvement in precision over standard aqueous analyses. Calibration curves are linear to at least 2 μM NH₄⁺. Sensitivity in seawater is 97% of that found in deionized distilled water due to a slight salt effect.     

Intercomparison of different methods for the determination of trace metals in seawater

During a cruise on the North Sea and the North East Atlantic, about 90 samples were obtained from various depths. Concentrations of cadmium, copper, lead, nickel and zinc were determined by atomic absorption spectroscopy after separation/concentration using two different extraction methods. One, using APDC and MIBK, was applied directly on board while the other, using a mixture of dithiocarbamates and freon, was applied after storage under acid conditions. About half of the samples were also analysed for cadmium, copper and lead using ASV. The results of these determinations are intercompared. Consistent results were obtained for cadmium with the two extraction methods and for lead with the freon extraction method and ASV. In the other cases discrepancies were found.     

A community-wide intercomparison exercise for the determination of dissolved iron in seawater

The first large-scale international intercomparison of analytical methods for the determination of dissolved iron in seawater was carried out between October 2000 and December 2002. The exercise was conducted as a rigorously “blind” comparison of 7 analytical techniques by 24 international laboratories. The comparison was based on a large volume (700 L), filtered surface seawater sample collected from the South Atlantic Ocean (the “IRONAGES” sample), which was acidified, mixed and bottled at sea. Two 1-L sample bottles were sent to each participant. Integrity and blindness were achieved by having the experiment designed and carried out by a small team, and overseen by an independent data manager. Storage, homogeneity and time-series stability experiments conducted over 2.5 years showed that inter-bottle variability of the IRONAGES sample was good (< 7%), although there was a decrease in iron concentration in the bottles over time (0.8–0.5 nM) before a stable value was observed. This raises questions over the suitability of sample acidification and storage.     

The determination of α-amino acids in seawater using a fluorimetric analyser

A method is described for the detection of free α-amino acids in the picomole range in seawater samples of less than 100 ml volume. The modifications made to a standard amino acid analyser to incorporate a fluorimetric detection system are described in detail, together with the methods for desalting the seawater samples on cation exchange resin and the concentration procedures prior to analysis. A complete analysis of up to 30 amino acids requires around 3 h with a detection limit of around 0.05 μg of an individual acid per litre. Twenty samples of seawater from different depths in the open Baltic have been analysed for their FAA contents together with 3 samples taken from the Kiel Fjord. The total FAA content of the samples ranges from 4.5 to 84 μg/l with a mean of around 25 μg/l. Five samples were hydrolysed prior to analysis in order to estimate the CAA content of the seawater. The values lay in the range 438–805 μg/l.     

A simplified resorcinol method for direct spectrophotometric determination of nitrate in seawater

A direct, spectrophotometric method has been adapted for quantitative determination of nitrate concentrations in seawater. The method is based on nitration of resorcinol in acidified seawater, resulting in a color product. The absorption spectrum obtained for the reaction product shows a maximum absorption at 505 nm, with a molar absorptivity of 1.7 × 10⁴ L mol^− 1 cm^− 1. This method has a detection limit of 0.5 μM and is linear up to 400 μM for nitrate. The advantage of this method is that all reagents are in aqueous solutions without involving cadmium granules as a heterogeneous reactant, as in conventional methods, and therefore is simple to implement. Application of the resorcinol to seawater analysis demonstrated that the results obtained are in good agreement with the conventional approach involving the reduction of nitrate by cadmium followed by diazotization.