Cold Vapor Mercury

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. 

---

Cold vapor mercury Light absorbed by atoms of mercury generated by chemical reaction at room temperature is measured An excellent technique for mercury analysis... 

Why is the cold vapor mercury technique good only for mercury ... 

Compare atomic absorption (both flame and graphite furnace), ICP, flame photometry, cold vapor mercury, hydride generation, atomic fluorescence, and spark emission in terms of ... 

ICP, cold vapor mercury, and hydride generation in regard to applicability and detection limit. 

Sasaki, K. and G.E. Pacey. 1990. The use of ozone as the primary digestion reagent for the cold vapor mercury procedure. Talanta 50 175-181. 

G. R. Boaventura, A. C. Barbosa, G. A. East, Multivessel system for cold-vapor mercury generation determination of mercury in hair and Psh, Biol. Trace Elem. Res., 60(1997), 153D161. 

Recommended conditions for flame and approximate values for ETA (graphite rod, etc.) atomizers are given in Table 2 for a number of elements important with regard to air pollution studies. Conditions are included in the table for the flame system used when hydrides of arsenic, antimony and selenium are generated and passed through the flame. Burrel [16] discusses generation of metal hydrides and cold-vapor mercury evolution techniques in great detail. 

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. 

Figure 12.3. Apparatus used for cold-vapor mercury absorption measurement...

Daniels, R.S. and Wigfield, D.C. (1989) The effect of experimental parameters on cold-vapor mercury atomic absorption determination. Speciation analysis of sulfhydryl-bound mercury. J. Anal. Toxicol., 13, 214-217. 

Figure 6.32 Automated cold vapor mercury analyzer. Mercury in the sample is reduced to Hg. The Hg vapor is separated from the solution by a gas-liquid separator and carried to the optical cell. The Hg vapor absorbs the 253.7 nm emission line from the Hg lamp and the amount of atomic absorption is measured using a solid-state detector. [Courtesy of Leeman Labs, Inc., Hudson, NH (www.leemanlabs.com).]...

Note. All detection limits were determined using elemental standards in dilute aqueous solution. All detection limits are based on a 98% confidence level (3 SD). Atomic absorption (Model 5100) detection limits were determined using instrumental parameters optimized for the individual element and EDL where available. ICP emission (Optima 3000) detection limits were obtained under simultaneous multielement conditions with a radial plasma. Detection limits obtained with an axial plasma are typically 5-10 times lower. Cold vapor mercury AA detection limits were determined with a FlAS -400 flow injection system with an amalgamation accessory. Hydride detection limits were determined with an MHS-10 Hydride system. Furnace AA (Model 5100/ZL Zeeman furnace) detection limits were determined using a L vov platform and 50 p.1 sample volumes. ICP-MS (Elan 6100) detection limits were determined using a 3 s integration. 

Most recently, amineboranes of the type L-BH3 (where L = NH3 tert-BuNHz MezNH Me3N) and sodium cyanotrihydroborate(III) (NaBH3CN) have been tested for efficacy of generation of elemental mercury and volatile hydrides of As(III), As(V), Sb(III), Sb(V), Bi(ni), Se(IV), Se(VI), Te(IV), and Te(VI). All of the reductants are suitable for efficient generation of cold-vapor mercury but only some of the amineboranes are suitable for hydride generation,... 

Figure 3 Typical cold-vapor mercury generation system.

As the cold-vapor mercury sample is already in the atomic state, there is no need of an atomizer, per se. The vapor, transferred directly from the cell or desorbed as a plug from a heated amalgamation trap, is commonly swept into a moderately heated (resistance wound heating to 200°C) 10 cm quartz T-tube located within the optical beam of a conventional AA spectrometer. Attenuation of an intense electrodeless discharge lamp line source at 253.7nm is used as a measure of the absorption. Alternatively, dedicated continuum source AA-based spectrometers fitted with long path absorption cells (30 cm) are frequently used to increase sensitivity and detection limit. 

Generally, the best detection limits are attained using ICP-MS or GFAA. For mercury and those elements that form hydrides, the cold vapor mercury or hydride generation techniques offer exceptional detection limits. Most manufacturers (e.g., Perkin-Elmer) define detection limits very conservatively with either a 95% or 98% confidence level, depending on established conventions for the analytic technique. This means that if a concentration at the detection limit were measured many times, it would be distinguished from a zero or baseline reading in 95% (or 98%) of the determinations. 

---