Mercury vapor, detection

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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. 

In order to measure the absorption of the beam of rays coming from the mercury vapor an ionization chamber with a thin mica window in it and containing methyliodide was set up opposite the window, F, and lead plates with holes in them were placed in the line of the beam so that only the radiation coming from the impacts of the electrons against the mercury entered the chamber with sufficient intensity to be detected. That this was the case in the actual experiments is indicated by the fact that no perceptible ionization current could be observed when the mercury pump was not running. A quadrant electrometer measured the ionization current. 

The analytic principles that have been applied to accumulate air quality data are colorimetry, amperometry, chemiluminescence, and ultraviolet absorption. Calorimetric and amperometric continuous analyzers that use wet chemical techniques (reagent solutions) have been in use as ambient-air monitors for many years. Chemiluminescent analyzers, which measure the amount of chemiluminescence produced when ozone reacts with a gas or solid, were developed to provide a specific and sensitive analysis for ozone and have also been field-tested. Ultraviolet-absorption analyzers are based on a physical detection principle, the absorption of ultraviolet radiation by a substance. They do not use chemical reagents, gases, or solids in their operation and have only recently been field-tested. Ultraviolet-absorption analyzers are ideal as transfer standards, but, as discussed earlier, they have limitations as air monitors, because aerosols, mercury vapor, and some hydrocarbons could, interfere with the accuracy of ozone measurements made in polluted air. 

Methyl mercury vapor is detectable by smell at concentrations well below those that on intermittent exposure could prove hazardous."... 

The photolysis of 1,3-dichlorotetrafluoroacetone has been studied by Bowles et al.,64 using the 3130 A. line from a medium pressure mercury vapor arc, and by Haszeldine and Nyman46 using a polychromatic source. The products of photolysis, as detected by gas chromatography and mass spectrometry, are given in Table III. 

Carbon Monoxide. Methods for determining carbon monoxide include detection by conversion to mercury vapor, gas filter correlation spectrometry, TDLAS, and grab sampling followed by gas chromatograph (GC) analysis. The quantitative liberation of mercury vapor from mercury oxide by CO has been used to measure CO (73). The mercury vapor concentration is then measured by flameless atomic absorption spectrometry. A detection limit of 0.1 ppbv was reported for a 30-s response time. Accuracy was reported to be 3% at tropospheric mixing ratios. A commercial instrument providing similar performance is available. 

Fig. 15.1. Chemical sensors for detection of mercury vapor. The thickness of the gold electrodes is 42 nm. The sensor geometry is shown schematically and cannot be used for recalculation of the total length.

The concentration of mercury vapor is determined from the calibration curve. Typical calibration curve is shown in Fig. 15.3. Detection limit corresponds to about lng/1 and can probably be improved by using differential configuration and/or temperature stabilization. 

Detection tags with high vapor pressure, particularly 2,3-dimethyl-2,3-dinitrobutane (DMNB), are commonly added to commercial explosives to facilitate the vapor detection of explosives with relatively low vapor pressure such as plastic explosives. Evans group [7] investigated the mechanism of the DMNB reduction at mercury electrodes in a dimethylformamide (DMF) medium, whereas Wang s team [8] recently... 

Mercury Detection Instrument Use any suitable atomic absorption spectrophotometer equipped with a fast-response recorder and capable of measuring the radiation absorbed by mercury vapors at the mercury resonance line of 253.6 nm. A simple mercury vapor meter or detector equipped with a variable span recorder also is satisfactory. 

The sensitive techniques require the release of CO from hemoglobin into a gas phase CO can then be detected directly by a number of methods such as infrared absorption, difference in thermal conductivity between CO and the carrier gas, amount of ionization following conversion of CO to methane, or the release of mercury vapor resulting from interaction of CO with mercuric oxide. 

Mercury, the only metallic element with significant volatility at room temperature, has been conventionally determined for many years by atomic absorption spectrometry, as the mercury vapor detector (W20) is based on this principle. Lindstrom (L7) used a flame to volatilize the mercury in the liquid sample, but determined its concentration in the exhaust gases with the mercury vapor meter after cooling and purification in a filter that removed particulate matter. The method is said to be capable of detecting 0.1 pg % of mercury in the original liquid sample... 

Jacobs et al. (Jl) developed a method for the determination of mercury in 0.1 ml blood. The specimen is digested in the cold and extracted with dithizone. The extract is decomposed in an electrically heated furnace and the mercury vapor is passed into a mercury vapor meter. The method is said to detect mercury in the nanogram range. 

Recent occupational health studies have focused on detecting early effects from mercury on the central nervous system. A dose-response relationship between subjective symptoms and/or impaired performance on psychological tests has been reported [61-64]. It is now conceded that an increased prevalence of neurotic symptoms may occur following long-term exposure to mercury vapor at concentrations exceeding 25 pg/ m [21]. An air concentration of 25 pg/ m roughly corresponds to a urinary excretion of 50 pg Hg/L. 

Yoshida et al. 1990, 1992). Following repeated exposure (5 weeks) of rats to mercury vapor (1 mg/m3), high levels were detected in the blood and brain (Warfvinge et al. 1992). The absorption of inorganic divalent mercury has not been measured, but it is estimated to be approximately 40% in dogs (Morrow et al. 1964). 

After 12-14 hours of exposure of rats to a relatively small amount of metallic mercury vapor (0.55 mg/m3), accumulation of mercury was observed within all cell types examined (ganglion cells, satellite cells, fibroblasts, and macrophages). Mercury has also been detected in dorsal root neurons and satellite cells of primates exposed for one year to mercury through amalgams in dental fillings or the maxillary bone (Danscher et al. 1990). 

Studies assessing mercury vapor exposure have suggested various ratios relating the concentration of mercury in the air (in g/m3) to the levels of mercury in the urine (in g/L). Such estimates include 1 1 (Bell et al. 1973), 1 1.22 (Roels et al. 1987), and 1 2.5 (Lindstedt et al. 1979 Rosenman et al. 1986). Urinary metallic mercury levels ranging from 0.05 to 1.7 g/L were detected in the urine of workers exposed to mercury vapor (>0.1 mg/m3) this elemental mercury represented <1% of the inorganic mercury content of the urine (Y oshida and Yamamura 1982). With increased exposure to mercury vapor (0.47-0.67 mg/m3), the amount of elemental mercury in the urine increased. A "rough" correlation between levels of metallic mercury vapor in air and mercury levels in blood and urine was established by Rosenman et al. (1986). They associated levels of 50 g/100 mL in blood and 250 g/L in urine with a mercury level in air of approximately 0.1 mg/m3 (8-hour TWA), and 28 g/100 mL in blood and 100 g/L in urine with a TWA of 0.05 mg/m3. Roels et al. (1987) found a correlation between daily mercury vapor exposure and blood or urine mercury levels in 10 workers employed for at least 1 year at an alkaline battery plant. The mercury levels in the air and the pre- or post-workshift levels of blood and urinary mercury correlated well (r=0.79-0.86 [blood] and r=0.70-0.80 [urine]). Based on a ratio of... 

Adults may receive higher mercury exposures from dermal contact if they work with mercury-contaminated soils. Mercury has been detected in soil and sediment at 350 and 208 sites, respectively, of the 714 NPL sites where it has been detected in some environmental media (HazDat 1998). No experimental information on dermal exposure related to the bioavailability of mercury or mercury compounds sorbed to soils was found. However, Hursh et al. (1989) conducted a study to determine the role of dermal exposure in the uptake of mercury vapor from air. These authors estimated that during an 8-hour day, a person would absorb through the skin only 2.6% of the mercury vapor retained by the lungs exposed to the same atmosphere. These authors also noted that half of the dermal uptake is lost through normal shedding of the stratum comeum. Therefore, dermal uptake of mercury adsorbed to soil is likely to be minor compared to other exposure pathways. Recent information from Hamly et al. (1997) showed that urine mercury levels in a Native American population living near an inactive mercury mine in Clear... 

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-... 

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