Mercury analysis direct determination

To date, a few methods have been proposed for direct determination of trace iodide in seawater. The first involved the use of neutron activation analysis (NAA) [86], where iodide in seawater was concentrated by strongly basic anion-exchange column, eluted by sodium nitrate, and precipitated as palladium iodide. The second involved the use of automated electrochemical procedures [90] iodide was electrochemically oxidised to iodine and was concentrated on a carbon wool electrode. After removal of interference ions, the iodine was eluted with ascorbic acid and was determined by a polished Ag3SI electrode. The third method involved the use of cathodic stripping square wave voltammetry [92] (See Sect. 2.16.3). Iodine reacts with mercury in a one-electron process, and the sensitivity is increased remarkably by the addition of Triton X. The three methods have detection limits of 0.7 (250 ml seawater), 0.1 (50 ml), and 0.02 pg/l (10 ml), respectively, and could be applied to almost all the samples. However, NAA is not generally employed. The second electrochemical method uses an automated system but is a special apparatus just for determination of iodide. The first and third methods are time-consuming. 

Lidums, V. and Ulfvarson, U. (1968) Mercury analysis in biological material by direct combustion in oxygen and photometric determination of the mercury vapour. Acta Chem. Scand., 22, 2150-2156. 

The automatic analysis system discussed above is used for the direct determination of mercury in water without using sampling vessels. In remote areas, this requires the use of an electrical generator with a voltage stabilizer and, if the air temperature is low, some insulation of the absorption cell of the mercury monitor. The system can be run on a normal 30 sec sampling-150 sec distilled... 

Examples of the AAS analysis of powdered samples, as well as such solid foods as chocolate and flour, are presented in [ 137]. [ 138J. The direct determination of mercury in soils, coal, and ash is di.scussed in [139]. ICP—OES (and ICP—MS) can also be transformed into a direct process through solid sample introduction and electrothermal pretreatment [140J. 

X-Ray Methods. In x-ray fluorescence the sample containing mercury is exposed to a high iatensity x-ray beam which causes the mercury and other elements ia the sample to emit characteristic x-rays. The iatensity of the emitted beam is directly proportional to the elemental concentration ia the sample (22). Mercury content below 1 ppm can be detected by this method. X-ray diffraction analysis is ordinarily used for the quaUtative but not the quantitative determination of mercury. 

Scarponi et al. [781] studied the influence of an unwashed membrane filter (Millpore type HA, 47 mm diameter) on the cadmium, lead, and copper concentrations of filtered seawater. Direct simultaneous determination of the metals was achieved at natural pH by linear-sweep anodic stripping voltammetry at a mercury film electrode. These workers recommended that at least 1 litre of seawater be passed through uncleaned filters before aliquots for analysis are taken the same filter can be reused several times, and only the first 50-100 ml of filtrate need be discarded. Samples could be stored in polyethylene containers at 4 °C for three months without contamination, but losses of lead and copper occurred after five months of storage. 

Procedures for the determination of 11 elements in coal—Sb, As, Br, Cd, Cs, Ga, Hg, Rb, Se, U, and Zn—by neutron activation analysis with radiochemical separation are summarized. Separation techniques include direct combustion, distillation, precipitation, ion exchange, and solvent extraction. The evaluation of the radiochemical neutron activation analysis for the determination of mercury in coal used by the Bureau of Mines in its mercury round-robin program is discussed. Neutron activation analysis has played an important role in recent programs to evaluate and test analysis methods and to develop standards for trace elements in coal carried out by the National Bureau of Standards and the Environmental Protection Agency. 

Filter Particulate Analysis. In the laboratory, the filters were immediately placed in a desiccator for 24 hrs and then weighed. The particulate concentration was calculated from this weight and the previously determined tare weight of the filter. The filters were analyzed for mercury by a procedure previously reported by the author (11) consisting of boiling the filters in concentrated nitric acid. After being cooled, aliquots of these solutions were pipetted into the interchangeable sample tubes and analyzed by the direct aeration technique. 

Mercury Determine as directed in the monograph for Iron, Reduced, but use 2 g of sample and 40 mL of Sodium Citrate Solution in preparing the Sample Solution, and prepare the Diluted Standard Mercury Solution as follows Transfer 4.0 mL of Mercury Stock Solution into a 250-mL volumetric flask, dilute to volume with 1 N hydrochloric acid, and mix (1 mL = 4 ig of Hg). Modify the first sentence of the Procedure to read Prepare a control by treating 1.0 mL of Diluted Standard Mercury Solution (4 p,g Hg) in the same manner. Sieve Analysis Determine as directed under Sieve Analysis of Granular Metal Powders, Appendix IIC. 

HMDE (hanging mercury drop electrode) [71, 72], gold-foil [73], copper-wire [74], tungsten-wire [75, 76] and pyrolytic graphite-coated tube [78] have been used as the electrodes for electrochemical deposition, and successfully applied to the determination of Cu, Cd, Pb, Zn, Hg and so forth. In atomic absorption analysis the electrodes are usually heated directly for atomization of metals. 

Since l is a thermodynamic quantity, the most reliable procedures for its determination are based on a thermodynamic analysis of adsorption data, possibly at low coverages. Adsorption data to be analyzed by the Gibbs adsorption equation can be obtained by measuring the interfacial tension y, the charge density crM or the differential capacity C. Direct y measurements are equilibrium measurements that can only be carried out on mercury. Direct charge measurements are conveniently carried out by the potential-step chronocoulometric technique, which can be... 

Relatively few rate constants are available for the alkyl homolysis reactions mainly because clean sources of the alkyl radical have proved difficult to find. Consequently, the data are not always reliable, but some check is available [64, 65] from thermochemical and kinetic data for the reverse reaction. Direct photolysis of azo-compounds and mercury-photosensitized decomposition of alkanes have so far provided the most reliable (although old) data [64]. For good results, the method depended on precise product analysis in the early stages of reaction, with equation (1.9) used to determine where Rabs and Rr r are the initial rates of formation... 

With the introduction in the late 1960s of very high sensitivity instrumentation for the analysis of air and soil gas for Hg, it became possible to determine Hg levels in the field. Air surveys were commonly carried out from vehicles mounted with a precious-metal collector. Mercury within measured volumes of air passing over the collector amalgamated with the precious metal, which was subsequently heated to release the Hg for analysis. A less sensitive alternative method was to pass air directly through a Hg analyser without pre-concentration. 

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