Mercury analysers

To be detectable, mercury must be present in elemental form. Thus for gaseous samples a thermal conditioner unit converts, in the presence of a catalyst, all mercury species present in the sample into elemental form. For liquid samples as polluted water, a first treatment by an acidic oxidizing mixture exchanges mercury compounds into Hg(II) ions that are then reduced to elemental mercury with a tin salt. 

When atmospheric mercury is to be measured, the mercury is preconcentrated by passing the sample through a trap containing gold-coated sand. This gold amalgamation enhances detection limits. The amalgam is next heated to desorb the mercury that is detected and measured either by AAS for concentrations within 

1 Analysis of an organic compound has revealed that it contains only carbon, hydrogen and oxygen. From the combustion, in a Pregl apparatus, of 

28 mg of this compound, 10.56 mg of carbon dioxide and 4.32 mg of water are obtained. 

What is the molecular formula of the compound knowing that mass spectrometry reveals no significant peaks above m/z = 89  

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The mercury analyses were conducted using a Coleman Instruments mercury analyser (MAS-50) equipped with a recorder. The aqueous sample solution was contained in a 250 ml Pyrex glass bubbler placed at one end of a sampling train employing nitrogen as the purging and carrier gas. A schematic diagram of the entire system is shown in Fig. 5.12. 

Fitzgerald WF (1975) Mercury analyses in seawater using cold trap preconcentration and gas-phase detection. In Gibb RP Jr (ed), Analytical Methods in Oceanography, American Chemical Society, Washington, DC, pp 99-109, 147... 

Since the introduction of the first fully automated laboratory-based mercury analysers in 1989, a number of other systems have been introduced. Around 20 different systems are available with varying levels of performance, and many claim to measure mercury at low levels. The analyst can therefore be forgiven if the determination of mercury is considered a trivial problem. Despite the various claims, the determination of low levels of mercury... 

Easterling et al. [161] has reported a rapid field screening method for the determination of elemental mercury in soil. This method involves thermal desorption of the mercury onto gold, followed by thermal desorption from the gold film mercury analyser. 

Dressman [694] used the Coleman 50 system in his determination of dialkylmercury compounds in river waters. These compounds were separated in a glass column (1.86mx2mm) packed with 5% of DC-200 plus 3% of QF-1 on Gas Chrom Q (80-100 mesh) and temperature programmed from 70 to 180°C at 20°C min-1, with nitrogen as carrier gas (50mL min ). The mercury compound eluted from the column was burnt in a flame ionisation detector, and the resulting free mercury was detected by a Coleman mercury analyser MAS-50 connected to the exit of the flame ionisation instrument down to 0.1 mg of mercury could be detected. River water (1L) was extracted with pentane-ethyl ether (4 1) (2 ><60mL). The extract was dried over sodium sulphate, evaporated to 5mL and analysed as above. 

Studies from New Zealand and the Faroe Island indicate that adverse effects in children can be correlated with maternal hair levels as low as 10-20 pg/g [44]. Mercury analyses conducted on a single human hair can be used to monitor daily variations in methyl mercury exposure among fish eaters [45,46], and have been utilized to track maternal fish consumption and risk of preterm delivery [47]. Other investigators [48] have utilized measurements of total mercury in hair, toenails and urine to assess exposures in a group of non-occupationally exposed women in relation to renal tubular effects. 

Table I. Representative Results of Mercury Analyses in Edible Fish Tissue (9)...

Mercury Analyses in Seawater Using Cold-trap Pre-concentration and Gas Phase Detection... 

See Figure 2 for saii5)ling locations). Each snow san5)le was collected with a 7.0 cm snow corer. Collected sanqjles were melted, pH analyzed and split into two portions. One aliquot was acidified (1.5 ml to 250 ml) for mercury analyses the other portion was kept frozen for future chemical analyses. 

The sample was passed through the spectrometer gas train using purified nitrogen. Ihe detection limit for water samples was 25 ng Hg/1. This limitation is introduced by mercury levels in distilled water blanks in the range of 10 to 20 ng Hg/1. All mercury analyses in aqueous samples were conducted within 14 days of san ile collection. 

Stream mercury levels varied frcm a low of < 25 ng/1 to as much as 72 ng/1. Of the forty-two mercury analyses, twenty-three were above the analytical detection limit of 25 ng/1. In order to calculate mean values, all sanples which were reported as < 25 ng/1 were consistently assessed a 12.5 ng/1 value. From available data, it appears that samples collected on October 3, 1978 and October 10, 1978 contained above average mercury levels. In addition, the November 16th sampling period also was consistently above mean mercury values for all collected stream samples. Nitrate concentrations ranged from a low of 0.1 to a iiaximum of 2.0 mg/1, with a mean value of 0.69 mg/1 which was comparable to precipitation concentrations. 

Trace metal concentrations in woody biomass are typically lower than trace metal concentrations in coal [17, 20, 44]. Table 4-11 summarizes trace metal concentrations from wood fuel found at various locations [44 - 47]. Table 4-12 summarizes trace metal concentrations in the urban wood waste cofired at the Bailly Generating Station. It should be noted that the mercury analyses shown in earlier references are typically below detection limits due to the nature of the fuel testing. Analyses performed after about 1998 are based upon the more recently... 

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