共查询到19条相似文献，搜索用时 243 毫秒
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超声波锌(卷)-镉法测定天然水中的硝酸盐 总被引：3，自引：0，他引：3
硝酸盐的测定方法很多,目前常采用镉－铜法和锌－镉法［２］。镉－铜法还原率高,无盐误差,为目前国际上公认的测定硝酸盐的标准方法［３］,但测定速度较慢,还原柱的前处理工作较为繁琐。锌－镉法测定硝酸盐简便快速,但其还原享受盐度影响很大,在淡水中其还原率仅为２０％左右。于志刚等［１］发现锌－镉法在盐度１０～７５时还原率保持恒定为７４％,从而采取向样品中加入固体海盐的方法来消除盐误差,获得较好结果。但该方法存在的问题是振荡采用往复式振荡器,体积庞大不适合现场操作。作者采用超声波振荡法,并对试验条件进行了改… 相似文献
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1967年以前,虽然测定海水中硝酸盐的方法很多,但都还存在一些问题。这些方法不是对低浓度硝酸盐的水样不够灵敏,就是受海水中其它组份干扰比较严重,或者测定步骤太繁,太费时多。Riley曾对这些问题进行过较详细的评论。1967年Wood和Armstrong等提出镉—铜还原法测定海水中硝酸盐的方法,由于该方法回收率高(99±1%),简便快速,成为测定海水中硝酸盐的例行分析方法。 不少作者对此方法做了改进。近来Gardner等为了简化分析操作,提出采用镉(丝)——铜还原硝酸盐的自动分析,仅需要几毫升水样即可。我们使用wood的 相似文献
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目的：建立菊花药材中铅、镉、砷、汞、铜 5 种有害金属元素的测定方法，并分析不同产地菊花药材重金属的分布情况。方法：采用电感耦合等离子体质谱法（ICP-MS)对不同产地菊花中铅、镉、砷、汞、铜5种重金属及有害元素进行含量测定。结果：铅、镉、砷、汞、铜 5种元素的精密度、重复性、稳定性RSD均＜3.0%，加样回收率（n=6）在87.9%～105.8%之间。采用系统聚类分析不同产地菊花药材中重金属含量，认为以江苏产地的菊花药材质量较好。结论：本研究建立的ICP-MS 具备灵敏度高、准确性好的优点，可用于菊花中5种重金属及有害元素的同时检测，为菊花的安全性评价提供科学依据，并为其他药材的测定提供参考。 相似文献
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一、前言 据文献〔1—4〕报导,海洋鱼贝类中铅、镉的含量一般分别在0.04一7μg/g、0.01—21μg/g(均为干重)范围之间,并且大部分样品中的镉都高于铅。虽然铅、铜、镉在弱碱性测试介质——柠檬酸三铵-乙二胺中也能测定,但由于引入的试剂空白较高,对测定样品中低含量的铅有影响,同时考虑到铅、镉的含量比较接近(铜含量0.1—500μg/g,干重),所以,本 相似文献
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海水中低浓度亚硝酸盐和硝酸盐测定方法综述 总被引：1，自引：0，他引：1
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。 相似文献
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A method has been developed for determination of15N isotope ratio in nitrate nitrogen, which is a major analytical step in tracer experiments for studies of nitrate metabolism
in the marine environment. The method is based on diazotization of nitrite with sulfanilic acid following reduction of nitrate
to nitrite by a cadmium-copper column. The diazonium compound is then subject to the azo coupling reaction with 2-naphthol,
and the azo dye formed is extracted by a solid phase extraction column. The dye eluted from the column is collected, and total
nitrogen and15N content of the dye are determined by mass spectrometry. Sulfanilic acid can also remove preexisting nitrite by heating the
sample under acidic conditions before passing through the cadmium-copper reduction column. The average recovery of nitrate
nitrogen was 86%. A procedure for reducing the background nitrogen that derives from the analytical operations has been developed;
background nitrogen was limited to about 0.25 μg-atomN. The variation in the background nitrogen levels reflects the range of error in15N determination of nitrate nitrogen by this method. Application of the present method to a15NO3
− isotope dilution experiment for determination of nitrification rate in sea water is demonstrated. 相似文献
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Hueiwang Anna C. Jeng Andrew J. Englande Reda M. Bakeer Henry B. Bradford 《Estuarine, Coastal and Shelf Science》2005,63(4):513-526
Urban stormwater runoff could contribute to the deterioration of water quality of a receiving water body. In this research, field studies and laboratory experiments were conducted to assess the microbial contamination resulting from urban stormwater runoff into the Lake Pontchartrain estuary. Fecal coliform, Escherichia coli and enterococci were used as indicator organisms. The specific objectives of the research were to examine the distribution of the indicator organisms in different environmental elements (water column, suspended particles and sediment) and to further investigate the mechanisms related to their fate. Results of the research indicated satisfactory water quality at the study sites during dry weather periods. However, a significant increase was observed in the concentrations of the indicator organisms in the water columns and sediment at specific study sites following a given stormwater event. Three to seven days were needed for the elevated indicator organisms to return back to their background levels in the water column and sediment, respectively. The mechanism of sedimentation contributed to a reduction in the microbial concentration in the water column, as the indicator organisms were found to attach to the suspended particles in the stormwater. The percentage of fecal coliform, E. coli and enterococci attached to the suspended particles was found to be within the range of 9.8–27.5%, 21.8–30.4%, and 8.4–11.5% of the total indicator organisms in the stormwater loaded into the estuary, respectively. About 75–80% of the total indicator organisms remained free-floating for some distance in the water column before dying off. 相似文献
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在充分认识传统沉降筒缺陷的基础上提出了"大型可温控自动搅拌沉降试验筒"。通过室内系列试验发现:(1)含沙量对长江口细颗粒沉降速度影响最大;(2)温度上升,沉速增加,但不同阶段影响程度有所不同;(3)含沙量越高,盐度对沉速的影响越小,含沙量相同情况下,长江口北槽悬沙枯季水温下盐度对沉速的影响在1.8~5.7倍左右;洪季水温下盐度对沉速的影响在1.5~2.2倍左右。(4)枯季最佳絮凝盐度在7左右,最佳絮凝含沙量为7 kg/m3;洪季最佳絮凝盐度在10~12左右,最佳絮凝含沙量为4.5kg/m3。本研究成果可望加深我们对细颗粒泥沙动力过程相关机理的认识,同时可为相关港口、航道的淤积机理分析,数学模型、物理模型研究工作提供一定技术参考。 相似文献
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Wave–current laboratory experiments have shown that the logarithmic current profile observed in pure current flows is modified due to the presence of waves. When waves propagate opposite the current, an increase in the current intensity is achieved near the mean water level, while a reduction is obtained for following waves and currents. With the aim of analyzing these nonlinear effects along the whole water column, an Eulerian wave–current model is presented. In contrast to previously presented wave–current models, the present is able to include the variation of the free surface elevation due to the wave motion and the effect of a non hydrostatic pressure field. Therefore it does not restrict its application to waves in shallow waters. Moreover, the model is able to simulate all the possible angles between waves and currents. 相似文献
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While acetate is generally regarded as an important intermediate in the mineralization of organic matter in anoxic sediment systems, some quantitative studies in marine systems (including our own) have measured acetate oxidation rates in excess of sulphate reduction rates where sulphate is known to be the principal electron acceptor. We revisited Skan Bay, Alaska, where we had previously made such observations, for a reexamination of acetate turnover. Measurements of acetate concentrations, production rate, oxidation rate and sulphate reduction rate as well as bioenergetic considerations led to the conclusion that acetate oxidation rate in 15–18-cm deep sediment is 1·1–1·5 μM h−1. The possibility that previous measurements were high because of a non-citric-acid-cycle pathway of acetate oxidation (suggested by recent laboratory studies) was excluded. It appears that our previous turnover measurements were high mainly because of high acetate concentrations. Procedures used for the isolation of porewater for acetate determination may influence results to an extent not previously recognized. 相似文献
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《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(7):1227-1245
Comparisons of the abundances and size distributions of marine snow (aggregated particles >0.5 mm in diameter) in the upper 100 m of the water column at ten stations off Southern California in the late afternoon with those in the same parcel of water the following morning, after nocturnal vertical migration by zooplankton had occurred, revealed the existence of a previously undescribed process affecting marine particle dynamics. Aggregate abundances increased overnight and changes were positively and significantly correlated only with the abundance of the common euphausiid, Euphausia pacifica, and with no other biological or physical factor. Moreover, mean aggregate size decreased and aggregate size distributions shifted toward smaller size classes when euphausiids were abundant. The only conclusion consistent with these findings was that euphausiids were physically disaggregating marine snow into smaller, more numerous aggregates through shear stresses generated while swimming. Video-recording of both tethered and free-swimming E. pacifica in the laboratory dramatically confirmed that aggregates passing within 8–10 mm of the animal's abdomen were fragmented either by entrainment and direct impact with the beating pleopods or by eddies generated during swimming. At the abundances observed in this study, swimming E. pacifica would have sufficiently disturbed 3–33% of the water column each night to disrupt the aggregates contained therein. This is the first evidence for the fragmentation of large particles by the swimming activities of zooplankton and suggests that macrozooplankton and micronekton play a significant role in the particle dynamics of the water column regardless of whether they consume particles or not. Disaggregation of marine snow by swimming and migrating animals may alter the sizes of particles available to grazers and microbial colonizers and reduce the flux of particulate carbon by generating smaller particles, which potentially sink more slowly and reside longer in the water column. This newly discovered process reduces carbon flux while simultaneously conserving carbon and provides a previously unconsidered link between animal behavior and the biogeochemistry of the sea. It may help explain the exponential reduction in particle flux with depth observed in parts of the ocean and help balance oceanic carbon models. 相似文献