Sequential injection spectrophotometric determination of nanomolar nitrite in seawater by on-line preconcentration with HLB cartridge

The unstable state of nitrite results in its very low concentration in seawater,which is below the limit of detection(LOD) of conventional techniques of analysis. Some sensitivity-enhanced methods have been proposed for the determination of nitrite at nanomolar level to illustrate the role of nitrite in the marine nitrogen cycle. However,most of previous reports are not widely accepted,because of their complexity and cost equipment or intensive labor requirement. In this study,a simple automatic system for the determination of nanomolar level nitrite using on-line preconcentration with spectrophotometric detection was described. An Oasis HLB cartridge was adopted to quantitatively enrich the pink-colored azo compound,formed from nitrite via Griess reaction. The cartridge was rinsed with water and ethanol(volume fraction is 55%,the same below) ,in turn,then eluted by an eluent containing 50% ethanol and 0.25 M(mol/dm 3 ) H 2 SO 4,and determined at 543 nm with a 2 cm path-length flow cell. Under the optimized experimental conditions,the calibration curve showed a good linearity in the range of 1.4-85.7 nM,and the LOD(3σ) was estimated to be 0.5 nM. The relative standard deviations of 7 measurements were 4.0% and 1.0% for the samples spiked at 7.1 and 28.6 nM,respectively. The recoveries for the different natural water samples were between 92.2%-108.4%. Each HLB cartridge could be reused for at least 50 times. As compared with other SPE methods,the advantages of this method included the free of interference from salinity variation and less sample consuming. The results of the application of the proposed method to natural water showed good agreement with liquid waveguide capillary cell detection method.     

A comparative study of three methods for the determination of iodate in seawater

A comparative study of three methods for the determination of iodate-iodine in seawater is described. In one method the iodate is determined polarographically while in the others the iodate is determined colorimetrically as iodonium ions. In one of the colorimetric methods each sample is pre-treated with excess iodine-water in an attempt to eliminate suspected interference from naturally occurring reducing agents. The tests were conducted on a selection of open-ocean and near-shore waters with iodate concentrations ranging from 0 to 60 μg 1^?1-I. The tests indicated that the polarographic method and the colorimetric method without iodine-water give the more reliable measurement of iodate concentration. Also, the method with iodine water was found to be in error especially at low iodate concentrations. Reducing agents, if present, were found not to interfere significantly.     

Liquid waveguide capillary cell for the spectrophotometric determination of nanomolar iodate concentrations in marine waters

A new spectrophotometric method based on a liquid waveguide capillary cell for an enhanced detection was developed to measure nanomolar iodate concentrations. This method has a detection limit and precision of 1–2 nmol/L, which is equivalent to 10% that of conventional methods, a recovery of 97.7%–104.0%, and a working range of 10–120 nmol/L. Water samples were collected from three estuaries and one coastal ocean for testing, and the proposed technique detected as low as 11 nmol/L and 18 nmol/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.     

A chemiluminescent technique for the determination of nanomolar concentrations of nitrate and nitrite in seawater

A chemiluminescent analysis technique for the determination of nanomolar quantities of nitrate, nitrate plus nitrite or nitrite alone in seawater is described. The method depends on the selective reduction of these species to nitric oxide which is then determined by its chemiluminescent reaction with ozone, using a commercial nitrogen oxides analyzer. The necessary equipment is compact and sufficiently sturdy to allow shipboard use. A precision of ±2 nM is claimed with analytical rates of 10–12 samples h^?1, and modifications are discussed to allow doubling the analytical rate.     

海水中低浓度亚硝酸盐和硝酸盐测定方法综述

海水中低浓度的亚硝酸盐和硝酸盐的测定方法主要有4种,即分光光度法(富集分光光度法和液芯波导分光光度法)、高效液相色谱法、荧光法和化学发光法。这些测定方法比传统的分光光度测定法有更高的灵敏度和更低的检测限,可以对海水中纳摩尔级低浓度的亚硝酸盐和硝酸盐进行测定。化学发光法和液芯波导分光光度法的自动化程度高,测定时对样品的需求量少,后者还实现了多个参数的实时现场测定,因而成为目前海水中低浓度亚硝酸盐和硝酸盐测定的主流方法,具有广阔的应用前景。     

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.     

离子色谱-电感耦合等离子体质谱联用测定海水中的IO3^-和I^-

研究了离子色谱-电感耦合等离子体质谱（IC-ICPMS）联用技术直接进样测定海水中IO3^-和I^-的方法．采用IonPacAG23离子色谱保护柱分离IO3^-和I^-,以浓度4．0mmol／dm3的KOH为流动相,流量为1．0cm3／min,每个样品的分析时间为2．5min．采用2．5×10^-3cm^3的进样量,IO3^-和I^-的检出限分别达到0．6和0．4nmol／dm2,可满足海水中碘形态的定量分析．该方法的IO3^-和I^-浓度范围在2．0nmol／dm3～2．0μmol／dm3．     

Sulfide interaction on colorimetric nitrite determination

It appears that in concentrations over 2μg-at S^2?/1, sulfide disturbs the determination of nitrite by the Shinn method. This disturbance can be counteracted by addition of an excess of Cd²⁺ or Hg²⁺ · Fe²⁺ was also tried out, but in this case the results were not satisfactory.     

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.     

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.     

Oscillopolarographic determination of microsillicon in seawater

A new oscillopolarographic method for the determination of Si (Ⅳ) is described in this paper. In the system HC1- Sb(Ⅲ) -Mo(Ⅵ) -NaCl-ethyl alcohol, Si (Ⅳ) with Sb (Ⅲ) and Mo (Ⅵ) form ternary heteropoly acid. The anion of ternary heteropoly is adsorbed on the dropping mercury electrobe and under proper electric potentials reduced quickly into heteropoly blue. The process of electrochemical reaction will produce a sensitive polarographic wave with peak potential at- 0. 30(Vs. SCE). The lower limit of determination is 8×10-8 mol/dm3. This method is sensitive, accurate and extremely rapid for the determination of micro-silicon in seawater.     

A sensor package for the simultaneous determination of nanomolar concentrations of nitrite, nitrate, and ammonia in seawater by fluorescence detection

A fluorescence-based chemistry has been developed for the detection of nitrite and nitrate (as excess nitrite following reduction of nitrate to nitrite). Detection limits are 4.6 and 6.9 nM, respectively. The technique capitalizes on the triple bond between the two nitrogen atoms within the diazonium ion formed via the well-known reaction between an acidified nitrite sample and an aromatic primary amine. Fluorescence of π-electrons within this bond allows this reaction to be probed with standard fluorescence spectroscopy. Reverse Flow Injection Analysis (rFIA) is used to correct for background fluorescence from leachates and naturally occurring dissolved organic matter (DOM). Comparisons of samples analyzed for nitrite with this technique and with a highly-sensitive chemiluminescent method [Braman, R.S., Hendrix, S.A., 1989. Nanogram nitrite and nitrate determination in environmental and biological materials by vanadium (III) reduction with chemiluminescence detection. Analytical Chemistry, 61 (24) 2716–2718] showed excellent agreement between the two methods (slope=0.9996 and r²=0.9956). These fluorescent nitrite and nitrate + nitrite chemistries were coupled in a sensor package with a modified version of a fluorescent ammonia chemistry [Jones, R.D., 1991. An improved fluorescence method for the determination of nanomolar concentrations of ammonia in natural waters, Limnology and Oceanography. 36(4) 814–819], which also has a nanomolar detection limit. The throughput rate of the fully automated three-channel instrumentation is 18 samples per hour. A field experiment demonstrated the capability of the nutrient sensor package to determine horizontal gradients in nitrate, nitrite, and ammonia in oligotrophic surface waters.     

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.     

The effect of temperature on carbon dioxide partial pressures in seawater

A correction formula is theoretically derived to evaluate the change in partial pressure of carbon dioxide in seawater upon heating. The constraints on the heating process are constant salinity, total alkalinity, and total carbon dioxide concentration. The result is

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. This equation fits δP_CO2/δt for open ocean seawater compositions to within approximately 9%. The almost constant 4.4%/°C effect is in agreement with that measured by Kanwisher (1960).     

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.     

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.