Mercury analytical techniques

Mercury layers plated onto the surface of analytical electrodes serve as Hquid metal coatings. These function as analytical sensors (qv) because sodium and other metals can be electroplated into the amalgam, then deplated and measured (see Electro analytical techniques). This is one of the few ways that sodium, potassium, calcium, and other active metals can be electroplated from aqueous solution. In one modification of this technique, a Hquid sample can be purified of trace metals by extended electrolysis in the presence of a mercury coating (35). 

Electrochemical analytical techniques are a class of titration methods which in turn can be subdivided into potentiometric titrations using ion-selective electrodes and polarographic methods. Polarographic methods are based on the suppression of the overpotential associated with oxygen or other species in the polarographic cell caused by surfactants or on the effect of surfactants on the capacitance of the electrode. One example of this latter case is the method based on the interference of anionic surfactants with cationic surfactants, or vice versa, on the capacitance of a mercury drop electrode. This interference can be used in the one-phase titration of sulfates without indicator to determine the endpoint... 

Fig, 16. Anodic stripping voltammogram for at the hanging mercury drop electrode. (Reprinted with permission from W. R. Heineman, in Water Quality Measurement The Modem Analytical Techniques , (H. B. Mark, Jr. and J. S. Mattson, eds.) Marcel Dekker New York, 1981)... 

The following analytical techniques seem to be adequate for the concentrations under consideration copper and nickel by Freon extraction and FAA cold vapour atomic absorption spectrometry, cobalt by Chelex extraction and differential pulse polarography, mercury by cold vapour atomic absorption absorptiometry, lead by isotope dilution plus clean room manipulation and mass spectrometry. These techniques may be used to detect changes in the above elements for storage tests Cu at 8 nmol/kg, Ni at 5 nmol/kg, Co at 0.5 nmol/kg, Hg at 0.1 nmol/kg, and Pb at 0.7 nmol/kg. 

Watling [491] has described an analytical technique for the accurate determination of mercury at picogram per litre levels in fresh and seawater. Mercury, released by tin (II) chloride reduction of water samples is amalgamated onto silver wool contained in quartz amalgamation tubes. The wool is then heated and the mercury thus released is flushed by argon into a plasma where it is excited. The emission signal thus produced results in a detection limit of 3 x 10 17 g and an analytical range 1 x 10 14 g-1 x 10"7 g. 

The most common analytical techniques available for mercury measurements are ... 

The Clean Air Act of 1970 declared beryllium, mercury, and asbestos as hazardous elements. Of the three, mercury is of particular interest to coal technologists. Other elements that exist as trace metals in coal and are suspected to be potentially detrimental to the environment include Pb, As, Sb, Zn, Se, Mo, Co, Li, V, Cr, Mn, Ni, etc. It is not the purpose of this book to create villains out of these elements, but to illustrate analytical techniques to determine how and in what amounts they are released in coal conversion processes. 

Partly because of this concern, the Wisconsin Department of Natural Resources, in cooperation with the Electric Power Research Institute, initiated an extensive study of Hg cycling in seepage lakes of north-central Wisconsin (14). The mercury in temperate lakes (MTL) study used clean sampling and subnanogram analytical techniques for trace metals (10, 17) to quantify Hg in various lake compartments (gaseous phase, dissolved lake water, seston, sediment, and biota) and to estimate major Hg fluxes (atmospheric inputs, volatilization, incorporation into seston, sedimentation, and sediment release) in seven seepage lake systems. 

A number of analytical methods were developed for determination of elemental mercury. The methods are reviewed in Refs. [1-4]. They include traditional analytical techniques, such as atomic adsorption spectroscopy (AAS), atomic fluorescence spectroscopy (AFS), and atomic emission spectroscopy (AES). The AAS is based on measurements of optical adsorption at 253.7 or 184.9 nm. Typical value of the detection limit without pre-concentration step is over 1 pg/l. The AEF is much more sensitive and allows one to detect less than 0.1ng/l of mercury... 

Schiitz, A., Skarping, G. and Skerfying, S. (1994) Mercury. In Techniques and Instrumentation in Analytical Chemistry, Vol. 15, Trace Element Analysis in Biological Specimens (eds Herber, R.F.M. and Stoeppler, M.). Elsevier, Amsterdam. 

Electrolytic deposition was used as a qualitative analytical technique in the early years of current electricity, but it was not until 1864 that quantitative electrochemical analysis commenced with the development of electrogravimetry by Wolcott Gibbs.76,77 Electrolytic techniques of analysis were greatly refined by Edgar Fahs Smith at the University of Pennsylvania, who introduced the rotating anode and double-cup mercury cathode. Smith s book on electrochemical analysis ran to six editions.78... 

An example is the determination of mercury in foodstuffs using cold vapour atomic absorption spectroscopy. The organic matter in foodstuffs is destroyed by wet oxidation. The mercury in solution is then reduced to the metallic state and released as a vapour in a stream of air. The quantity of mercury vapour in the air stream is measured by cold vapour atomic absorption spectroscopy. This part off the method is called the end determination. Often, as in this example, the end determination is equivalent to the analytical technique for the method. 

Mercury(I) is assumed to be of minor importance as an environmental contaminant due to the instability of Hg complexes with common atmospheric ligands (e.g. OH and S03 , etc.). However, reliable trace analytical techniques for Hg in the gaseous or aqueous phase are unavailable. 

One of the most important problems in oceanography and water resources science is the effect of the concentrations and concentration changes of trace metal ions on the nature of the water system (1-6). Recently, there has been much interest in the apparent increased concentration of metal ions such as mercury, lead, and iron. This concern is, at best, speculative since there are insuflBcient analytical techniques to establish baseline normal concentrations with the precision expected of good analytical methods. For example, there has been tremendous publicity concerning the level of mercury concentrations in edible fish in Lake St. Clair (7, 8, 9). Even in extreme cases, there was considerable disagreement in the true mercury concentrations in the fish analyzed. Rottschafer, Jones, and Mark (9) conducted a comparative study in which a homogenous sample of Coho salmon flesh was dis-... 

Bortoli A, Dell Andrea E, Gerotto M, et al. 1991. The analytical techniques for total mercury (Hg), methyl mercury (MeHg), and selenium (Se) determination in a fisherman and fishing families group of north Adriatic coast. Acta Chimica Hungarica 128(4-5) 573-580. 

Roels et al. [38] points out that the analytical techniques identified in Table 1 are not easily available and are not well-suited for routine biomonitoring of occupational or environmental exposures. Instead, indirect biomarkers such as urinary enzymes are often used with success to evaluate mercury exposure and injury. Zalups [35] identifies numerous methods used to detect renal tubular injury induced by mercury. These methods monitor the urinary excretion of enzymes that leak from injured and necrotic proximal tubules, including lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and N-acetyl-P-D-glucosaminidase (NAG). Although advocated by Zalups (35) to detect renal tubular injury, Mason et al. (48) questions the practical utility of such biomarkers in occupational surveillance. According to Mason et al., small increases in NAG, leucine... 

Electrocapillary methods, described in Sections 13.2 and 13.3, are very useful in the determination of relative surface excesses of specifically adsorbed species on mercury. As discussed in Section 13.4, such methods are less straightforward with solid electrodes. For electroactive species and products of electrode reactions, the faradaic response can frequently be used to determine the amount of adsorbed species (Section 14.3). Nonelectro-chemical methods can also be applied to both electroactive and electroinactive species. For example, the change in concentration of an adsorbable solution species after immersion of a large-area electrode and application of different potentials can be monitored by a sensitive analytical technique (e.g., spectrophotometry, fluorimetry, chemiluminescence) that can provide a direct measurement of the amount of substance that has left the bulk solution upon adsorption (7, 44). Radioactive tracers can be employed to determine the change in adsorbate concentration in solution (45). Radioactivity measurements can also be applied to electrodes removed from the solution, with suitable corrections applied for bulk solution still wetting the electrode (45). A general problem with such direct methods is the sensitivity and precision required for accurate determinations, since the bulk concentration changes caused by adsorption are usually rather small (see Problem 13.7). 

Lindh U and Johansson E (1987) Protective effects of selenium against mercury toxicity as studied in the rat liver and kidney by nuclear analytical techniques. 

Examples of applications of X-ray spectrometric analytical techniques to elemental determinations in a variety of materials are presented in Table 2.12. Some recent applications papers may be mentioned. Total reflection XRF has been applied by Xie et al. (1998) to the multielement analysis of Chinese tea (Camellia sinensis), and by Pet-tersson and Olsson (1998) to the trace element analysis of milligram amounts of plankton and periphyton. The review by Morita etal. (1998) on the determination of mercury species in environmental and biological samples includes XRF methods. Alvarez et al. (2000) determined heavy metals in rainwaters by APDC precipitation and energy dispersive X-ray fluorescence. Other papers report on the trace element content of colostrum milk in Brazil by XRF (da Costa etal. 2002) and on the micro-heterogeneity study of trace elements in uses, MPI-DING and NIST glass reference materials by means of synchrotron micro-XRF (Kempenaers etal. 2003). 

Some of the difficulties in the unbiased determination of certain trace elements in biological materials may be due to problems of speciation. The range of complex organo-metallic species that can be found in nature is very wide (Frausto da Silva and Williams, 1991). In carrying out an analysis for a particular element in any type of biological fluid or tissues, major assumptions are made concerning the precise chemical composition of element species present. Different analytical techniques will have different sensitivities towards particular element species. Much of the early understanding of the special analytical problems posed by element speciation comes from studies of arsenic (Buchet et al., 1980 Buchet et al., 1981) and mercury (Clarkson, 1983). Problems with other metals remain to be resolved and may require considerable analytical sophistication such as in the analysis of chromium speciation (Urasa and Nam, 1989). 

On the way towards final, reliable analytical results, the following steps, each of them equally important, must be considered (1) Sample collection, (2) sample storage, (3) sample preparation, and (4) mercury quantification. This review is focused on different mercury quantitation techniques, but also the other steps will be discussed in some detail. 

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