| Ammonium,sulfide,and copper(Ⅱ)play key roles in the biogeochemical cycle of oceanic anoxic zones.Therefore,it is critical to obtain their accurate concentrations data.Although there are many methods for detecting ammonium,sulfide,and copper(Ⅱ)in seawater,none of them can meet the requirements for analyzing sample on field at trace concentration level in open ocean automatically.Moreover,in addition to efficient and accurate analysis methods,a reliable sampling technique is also necessary.The existing oceanic profile samplers have some drawbacks,including low sampling resolution and inability to add protective reagents simultaneously while sampling,which might lead to the transformation and loss of ammonium and sulfide during the sampling process.In response to the above requirements and deficiencies,two highresolution oceanic profile samplers and onboard analysis methods of trace ammonium,sulfide,and copper(Ⅱ)in seawater have been developed in this study,and their performance has been investigated in several field applications.The main contents and results are as follows:(1)By utilizing the micro plunger pump as sampling pump and reagent pump,a high-resolution profile continuous sampler and a high-resolution profile dispense sampler were developed,respectively,and the performance of the two samplers was optimized.Both samplers could add a protective reagent while sampling.The highresolution profile continuous sampler was easy to operate and suitable for the collection of a small volume of sample,while the high-resolution profile dispense sampler was ideal for occasions where a large sample volume(15 mL)and a longer sample storage duration were required.(2)Based on the derivatization reaction of ammonium with o-phthalaldehyde(OPA)and sulfite(Na2SO3)under alkaline conditions,a flow injection analysis of trace ammonium in seawater was established by coupling online solid phase extraction(SPE)and fluorescence detection.The method detection limit(MDL)was 2.0 nmol L-1,and the relative standard deviation(RSD)was 3.52%(n=12)for a sample spiked at 40 nmol L-1 ammonium.The sample throughput was 7-9 h-1,and the stopped-flow time could be adjusted depending on the concentration of ammonium in the seawater samples.A new method for calculating the blank value by experiment was proposed.The calculation method can also be introduced to the determination of other trace analytes where the matrix effect cannot be neglected.The analytical method was free of effects of salinity and carry-over.The method has been successfully applied for shipboard underway determination of ammonium in the northeastern South China Sea,the Xiamen and Lianjiang coastal area(China),and for onboard measurements of ammonium concentration of discrete samples in three vertical profiles during a cruise in the South China Sea.(3)Based on the reaction of dissolved sulfide with N,N-dimethyl-pphenylenediamine dihydrochloride(DMPD)and iron(Ⅲ)to produce methylene blue in a sulfuric acid medium,a colorimetric method was established for the determination of trace sulfide in seawater using reverse flow injection analysis(rFIA)coupled with a liquid waveguide capillary cell(LWCC).The MDL was 1.67 nmol L-1,with RSD of 2.01%(n=14)for samples spiked at 100 nmol L-1 sulfide.The recoveries ranged between 96.2%and 106%,and the sample throughput was 24 h-1.The method was not affected by salinity or carry-over.The linear range was extended from 5.5-1200 nmol L-1 to 0.25-32 μmol L-1 by replacing the LWCC with a 3 cm flow cell while the reagent concentrations and other parameters were kept the same.The method was successfully applied for shipboard underway determination of dissolved sulfide in the surface waters of the Jiulong Estuary(China).(4)On the basis that copper(Ⅱ)can catalyze the fading reaction of K3Fe(CN)6 in an acidic medium,an automated and simple catalytic kinetic spectrophotometric method for copper(Ⅱ)in seawater was established,which was coupling with an LWCC and rFIA,and without the need for any extraction or pre-concentration steps.The RSDs of blanks and samples spiked at 5 nmol L-1 copper(Ⅱ)were 1.52%(n=13)and 1.10%(n=13),respectively.The method was shown to have high sensitivity with a detection limit of 0.15 nmol L-1 in a pure water matrix and 0.23 nmol L-1 in a seawater(salinity 35)matrix.Linearity was achieved within the range of 0.45-15 nmol L-1 in a pure water matrix and 0.69-10 nmol L-1 in a seawater matrix,while the upper limits could be extended by using a shorter reaction coil.The method was successfully applied to the underway and onboard determination of copper(Ⅱ)concentrations in the Jiulong Estuary and Xiamen coastal surface waters.The distribution of copper(Ⅱ)concentration was obtained,which verified the feasibility of the method and system.(5)In combination with either one of the high-resolution oceanic profile samplers with the onboard analysis methods of trace ammonium,sulfide and copper(Ⅱ),field applications were successfully carried out in the coastal waters from Xiamen to Fuzhou,as well as the Yangtze River Estuary and its adjacent waters,and the preliminary results were discussed.Both samplers showed good stability.The analytical results of the samples collected by the two samplers had no significant difference from those collected by a conventional CTD,indicating that the samplers were reliable and the collected samples were highly representative. |
PDF Full Text Request