Elemental mercury vapor measurements

The elemental mercury vapor measurements were made in areas of Northern California known or suspected to be sites of mercury contamination. Early reports (2) cited only two small industries in California as having mercury-bearing eflfluents. Other sites were visited because of suspected emissions or were simply discovered during reconnaissance traversing. Thirteen specific sites of contamination were located (Figure 3). Of these, seven were clearly natural, and six were most likely cultural. Table I summarizes the data obtained at these sites. 

In recent years, increasing attention has been paid to human exposure to mercury via dental amalgams (Skare 1995). Exposure results from elemental mercury vapor released from amalgams that is either inhaled directly or swallowed after dissolution in saliva. A Jerome 511 Gold Film Mercury Vapor Analyzer (Arizona Instrument Corp., Jerome, AZ) has been used to measure mercury vapor released from amalgam during routine dental procedures (Engle et al. 1992) or at other times to establish baseline... 

Jerome 43IX Mercury Vapor Analyzer) was used by Chien et al. (1996) to measure elemental mercury vapor released from dental amalgams in the oral cavity and was reported to have a sensitivity of 0.003 mg/m3. Absorbed mercury can be measured using blood and urine measurements as described below. 

Only elemental mercury vapor was measured. Thus, these data alone cannot be taken as a guide to the total mercury content in the air. The rapid disappearance of the anomalous plumes may reflect not just the dispersion or deposition of the mercury but also the chemical combination of the elemental form into a combined form undetectable by the instrumentation. The rapid disappearance of the Berkeley plume as it blew across the freeway may indicate a chemical reaction catalyzed by the exhaust emissions from the freeway traflSc. 

A number of workers have described methods for the determination of mercury in which the mercury is first reduced to the element or collected as the sulfide on a cadmium sulfide pad. It is then volatilized into a chamber for measurement. These techniques are extremely sensitive. Thillez108) recently described a procedure for urinary mercury in which the mercury is collected on platinum and then volatilized into an air stream. Rathje109) treated 2 ml of urine with 5 ml of nitric acid for 3 min, diluted to 50 ml, and added stannuous chloride to reduce the mercury to the element. A drop of Antifoam 60 was added and nitrogen was blown through the solution to carry the mercury vapor into a quartz end cell where it is measured. Six nanograms of mercury can be detected. Willis 93) employed more conventional methods to determine 0.04 ppm of mercury in urine by extracting it with APDC into methyl-n-amyl ketone. Berman n°) extracted mercury with APDC into MIBK to determine 0.01 ppm. 

Mercury is the only metal that is a liquid at ordinary temperatures. It is therefore also the only metal that has a significant vapor pressure at ordinary temperatures. For this reason, it is possible to obtain mercury atoms in the gas phase for measurement by atomic absorption without the use of thermal energy. It is a matter of chemically converting mercury ions in the sample into elemental mercury, getting it in the gas phase, and channeling it into the path of the light of an atomic absorption instrument. 

For the determination of traces and ultratraces of Hg, As, Se, Te, As and Bi the formation of the volatile mercury vapor or of the volatile hydrides of the appropriate elements is often used, respectively. This allows a high sampling efficiency to be achieved and accordingly a high power of detection. The absorption measure-... 

Measurement was by cold-vapor atomic absorption (CVAA), which is based on the reduction of ionic mercury to the elemental form by divalent tin. The resultant elemental mercury is swept by a gas stream through a quartz-windowed absorption cell which is placed in the beam of a mercury lamp of an atomic absorption spectrometer. Hatch and Ott (11) optimized this measurement system in their study of the mercury content of geological samples. Since their work, this method of mercury measurement has gained widespread popularity because of its sensitivity and relative simplicity. Two recent reviews which cover the Hatch and Ott technique and its subsequent modifications have appeared (17,18). 

Outline of Method. A sample is weighed into a beaker, dissolved in benzene 2-propanol, and burned in an oxy-hydrogen flame using a Wickbold combustion apparatus. The combustion products are collected in a 5% sulfuric-nitric acid mixture containing potassium permanganate. Prior to measurement, trapped mercuric salts are reduced to elemental mercury with tin (II) chloride. The mercury is then swept out of solution and measured by cold-vapor atomic absorption spectroscopy. 

The use of high-sensitivity, portable, rapid-response gas-analyzing equipment has led to the detection of several previously unknown elemental mercury plumes associated with both natural and industrial sources. In Northern California these anomalies were detected in a brief reconnaissance program and hence represent only a sampling of the mercury vapor plumes likely to exist in the area. An inventory of elemental mercury plumes can be obtained in any area by using a high-sensitivity, portable, rapid-response mercury detector mounted in a mobile laboratory for measurement while in motion. 

Two additional commercially available atomizers (really analysis techniques with unique atomizers) must be discussed, because they are extensively used in environmental and clinical analysis. They are the cold vapor-AAS technique (CVAAS) for determination of the element mercury, Hg, and the hydride generation technique (HGAAS) for several elements that form volatile hydrides, including As, Se, and Sb. These elements are toxic federal and state laws regulate their concentrations in drinking water, waste-water, and air, so their measurement at ppb concentrations is very important. Because... 

Mercury is unusual in that it exists as gas phase free atoms at room temperature. Elemental mercury is a hquid at room temperature, but a liquid with a very high vapor pressure. So it is not necessary to apply heat from a flame or furnace to measure mercury vapor by AAS. 

Determination of traces and ultra-traces of Hg, As, Se, Te, As, and Bi is often by formation of either volatile mercury vapor, or of the volatile hydrides. This gives a high sampling efficiency and power of detection. The absorption measurement is often performed in a quartz cuvette. Hg, for instance, can be transported after reduction by means of a carrier gas. For the absorption measurement no heating is required. The other elements are reduced to the volatile hydride, which is then transported with a carrier gas flow (argon or nitrogen) into a cuvette. In order to dissociate the hydrides thermally, the quartz cuvette must be heated to a temperature of 600 - 900 °C. 

Elemental composition Hg 79.40%, C 9.51%, N 11.09%. Aqueous solution is analyzed for mercury metal by AA-cold vapor techniques or by ICP/AES (see Mercury). The cyanide ion may be measured by cyanide ion-specific electrode or by ion chromatography after appropriate dilution. 

Elemental composition Hg 92.61%, 0 7.39%. The compound is digested in nitric acid and mercury in an appropriately diluted acid extract and then is measured by cold-vapor AA or by ICP. The compound may be characterized nondestructively by x-ray methods. 

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