Mercury detection

Fig. 7.1S Schematic layout of mercury detection system showing valve sequencing for collection, flush and measurement.

Li and coworkers synthesized the novel IL l-butyl-3-trimethylsilylimid-azolium hexafluorophosphate and demonstrated its utility for liquid/ liquid extraction of inorganic mercury. Using o-carboxyphenyl diazoamino p-azobenzene as a chelator to form a stable neutral complex with the metal ion, the authors demonstrated selective extraction into the hydrophobic IL phase [19]. When sodium sulfide was added to the IL phase, the mercury ion was back-extracted into the aqueous layer, providing an avenue for recycling the IL. The authors report extraction and back-extraction efficiencies of 99.9 and 100.1%, respectively, for a 5.0 pg/L aqueous mercury standard. The mercury detection limit was 0.01 ng/mL in water and the method was successfully applied to detecting trace mercury in natural water samples. 

Chemical sensors for mercury vapour, based on QMB, provide sensitivity of 0.7-5 ng/1 [24]. Reversibility is reached by heating the sensor a microheater can be integrated on the sensor surface. This detection principle was also used by several other groups, for example [7,9,25]. Another realization of this transducing principle is based on exploitation of gold-coated microcantilevers for mercury detection [21,22]. 

A flame AAS (FAAS) detector can monitor the GC effluent continuously to provide on-line analysis. However, as the gas flow rates for the flame are quite high, the residence time in the flame is short, and this can adversely affect the detection limits. Detection limits in the microgram range are usually achieved. Improved detection limits can be obtained if the additional techniques of hydride generation or cold vapour mercury detection are used as described in Section 4.6. 

Apparatus Use a Mercury Detection Instrument as described and an Aeration Apparatus as shown in Fig. 16 under Mercury Limit Test, Appendix IIIB. For the purposes of the test described in this monograph, the Techtron AA-1000 atomic absorption spectrophotometer, equipped with a 10-cm silica absorption cell (Beckman Part No. 75144, or equivalent) and coupled with a strip chart recorder (Varian Series A-25, or equivalent), is satisfactory. 

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. 

Note The absorption cell will vary in optical pathlength depending on the type of mercury detection instrument used. 

Cold vapor mercury detection limits were determined with a FIAS(ji )-100 or FIAS-400 flow-injection system with amalgamation accessory. The detection limit without an amalgamation accessory is 0.2/ig/L with a hollow cathode lamp, 0.05 /ig/L with a System 2 electrodeless discharge lamp. (The Fig detection limit with the dedicated FIMS(ji )-100 or FIMS-400 mercury analyzers is <0.010/ig/L without an amalgamation accessory and <0.001 /ig/L with an amalgamation accessory.) Flydride detection limits shown were determined using an MFlS-10 Mercury/Flydride system. 

Method Able to distinguish methyl mercury Detection limit (ppm) Reference... 

A mong the preferred analytical methods for determining mercury con-centrations in natural samples save been closed system reduction-aeration procedures using mercury detection by gas phase atomic absorption or atomic fluorescence spectrophotometry (I-I5). In studies in the oceanic regime, where the amount of mercury in a liter sample of open-ocean seawater can be as small as 10 ng (11,15,16,17), a. pre-concentration stage may be required. The lowered detection limits which accompany a preliminary concentration step are most desirable when the sample materials are rare or in limited quantities such as carefully collected open-ocean biota, open-ocean rain water, and deep-ocean seawater. 

Analytical Procedure. The cold-trap gas phase mercury detection system was designed and used for both laboratory and shipboard measurements of mercury in seawater. The Coleman Instruments mercury analyzer (MAS-50) was incorporated into the analytical system because of its portable and convenient design. However, the effective use of this simple one-element atomic absorption unit requires scrupulous attention to blank determinations for each seawater sample. For example, the undetected presence of either naturally occurring or sampling induced volatile organics which may absorb at the mercury wavelength in the seawater sample can be a serious error. Such artifacts were observed when acidifled seawater samples were stored in low density polyethylene bottles (21), Therefore, the analytical procedure used to determine the mercury concentration in a seawater sample consists of the following steps ... 

A summary of the mean, minimum, and maximum tissue concentrations of mercury detected for two of the sampled species with the widest geographical distribution the largemouth bass and the channel catfish are given in Tables 5-8 and 5-9. As Table 5-8 shows, the maximum mercury residues reported for the largemouth bass exceeded the FDA action level (1 ppm) in 15 of the 25 states that collected and analyzed tissue samples for this species. The highest maximum mercury concentration reported for this species was 4.36 ppm, reported by Florida. Table 5-9 shows the maximum mercury residue reported for another widely distributed species, the channel catfish. While the maximum mercury residues reported for this species are not consistently as high as those for the largemouth bass, maximum residues in... 

Costanzo RB, Barry EF. 1988. Alternating current plasma detector for selective mercury detection in gas chromatography. Anal Chem 60(8) 826-829. 

Figure 3.5 Schematic representation of the colorimetric mercury detection method for Hg2+ that relies on thymidine-Hg2+-thymidine coordination chemistry and...

The amounts of mercury detected by optimized GF-AAS techniques are generally smaller than those detectable by most other techniques. The minimum detectable concentration is, however, in clear favour of optimized CV techniques, because of the possibility to use considerably larger samples for a single determination. 

McNerney, J.J., Busek, P.R., and Hanson, R.C. (1972) Mercury detection by means of thin gold film. Science, 178,611-612. 

The EPA method 245.7 uses a system similar to Fig ure IA2-I for mercury detection. In some commercial. systems, the digesrion-oxidation step is also automated. 

The concentration of total mercury in air can be determined with high precision and accuracy. There are still, however, analytical problems in separating and analyzing all the specific mercury compounds that can be present in air. Since concentrations of organomercurials are so low, a preconcentration step has to be employed. In general, two approaches are possible for measurements of mercury compounds in air (1) Selective adsorption methods (usually coupled with nonselective detectors), in which the separation is operationally defined and a true species identification is not obtained (therefore it is not clear whether the species determined are the actual mercury compounds present in the atmosphere). (2) Gas chromatographic methods, which allow identification of various organic species by their unique retention times and specific mercury detection system. The... 

Mercury detection is also extremely important from the standpoint of public health. We have recently carried out studies on the detection of Hg itself at a BDD electrode using cyclic voltammetry (CV) and DPASV. The nature of the electrode material is an important consideration for trace detection. In the past, the determination of mercury in water by anodic stripping... 

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