Mercury absorption reactions

In this chapter electronically excited atoms are classified into two groups. The lirst group of excited atoms are those that are formed by resonance absorption and decay rapidly by fluorescence if not quenched by collisions with foreign gases. Examples are electronically excited Hg, Cd, H, Ar, Kr, and Xe atoms. Of these Hg(,/>1) atoms and their reactions have been most extensively studied. The mercury sensitized reactions provide a convenient way to generate atoms and radicals in the spectral region where many molecules do not absorb. 

Chemical analysis of expl reaction products has been performed utilizing spectroscopic methods. A study of the thermal decompn of Tetrazene at 90° has demonstrated that substantially complete conversion to 5-aminotetra-zoie is effected (Ref 69). Spectroscopic evidence has indicated that this product is derived from both the side chain (guanyl azide) and the Tetrazole ring. Utilizing the unique-to-mercury absorption line at 2536.5a, mercury (II) concn... 

Procedure Transfer 100 mL of Standard Solution to a 300-mL mercury analysis reaction vessel, add 2 drops of a 1 20 potassium permanganate solution, and mix (the solution should be purple add additional permanganate solution, drop-wise, if necessary). Add 5 mL of 11 A nitric acid, stir, and allow to stand for not less than 15 s. Add 5 mL of 18 A sulfuric acid, stir, and allow to stand for not less than 45 s. Add 5 mL of a 3 200 hydroxylamine hydrochloride solution, stir, and allow to stand until the solution turns light yellow or colorless. Add 5 mL of a 1 10 stannous chloride solution, immediately insert the aerator connected to an air pump, and determine the maximum absorbance of the treated Standard Solution at the mercury resonance line of 253.65 nm, with a suitable atomic absorption spectrophotometer equipped with a mercury hollow-cathode lamp and an absorption cell that permits the flameless detection of mercury. 

Inorganic mercury was also isolated as methyl mercury upon reaction with tetra-methyl tin ° The initial extracts were subjected to thiosulfate clean-up, and mercury was isolated as the bromide derivative. The method yielded good agreement between gas-chromatographic and atomic absorption spectrometric data. Twenty-four samples were analyzed daily on a routine basis. Organomercurials could also be determined and the differences from inorganic mercury could be detected by these gas-chromatographic methods ... 

This secondary reaction starts at about 180°C, but the mass must be heated to 350—400°C to bring the reaction to completion and produce a nitrate-free product. The off-gases are extremely corrosive and poisonous, and considerable attention and expense is required for equipment maintenance and caustic-wash absorption towers. Treatment of the alkaline wash Hquor for removal of mercury is required both for economic reasons and to comply with governmental regulations pertaining to mercury ia plant effluents. 

A diagram of a suitable apparatus is shown in Fig. 21.7. The mercury vapour is flushed out of the reaction vessel by bubbling argon through the solution, into the absorption tube. 

When this resin was exposed as a thin film to the UV radiation of a medium pressure mercury lamp (80 W aiH), the crosslinking polymerization was found to develop extensively within a fraction of a second (18). The kinetics of this ultra-fast reaction can be followed quantitatively by monitoring the decrease of the IR absorption at 810 an-1 of the acrylic double bond (CHCH twisting). Figure 8 shows a typical kinetic curve obtained for a 20 pm thick film coated onto a NaCl disk and exposed in the presence of air to the UV radiation at a fluence rate of 1.5 x 10 6 einstein s-1 cm 2. 

The interface provides efficient transfer of samples into the Merlin, and, most importantly, a rapid flush-out there is no hold up of mercury (which is a feature of the commonly used atomic absorption techniques). To aid the transfer of mercury vapour, the tin(II) chloride regime is used, together with a gas/liquid separator designed for this task. Mercury is sparged from the reaction vessel into the Merlin Detector. Full automation is provided by using a simple standard DIO card fitted into an IBM compatible computer system with the PSA Touchstone software. This is an easy-to-use menu-driven system which controls the modules used in the instrumentation, calibrates the system, collects, collates and reprints the results, and which finks to host computer systems. 

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