Date of Award
Doctor of Philosophy (PhD)
Although trace analysis procedures for the analysis of total mercury have been available for a number of years, a major shortcoming of the procedures has been the inability to differentiate between the exact chemical forms of mercury species in solution. This is needed due to the varlng toxicity of the different species. An investigation was made of the possible analytical procedures which could be used for a separation and quantitation of mercury (0), mercury(I), mercury(II), methyl- and phenylmercury(II). The method of flameless atomic absorption spectroscopy (PAA) was used to detect mercury vapor produced by reduction of all mercury species or disproportionation of mercury(I) In an aeration cell. To increase the sensitivity of this method a new design of aeration cell was tested. The parameters that affected the instrument response were investigated and fixed to give a reproducible instrument response. These parameters were sample volume, carrier gas flow rate, . aeration solution volume, and concentration of the sample analyzed.
The stability of various mercury solutions was investigated to have available standard solutions to be used for calibration of the PAA spectrophotometer. Mercury(II) solutions in the ppb range could not be stored for more than one working day without the formation of mercury(I) in the solution. This was suspected to have been caused by the oxidation of water by mercury(II). Solutions containing mercury(O) were found to be air oxidized to mercury(I). The preparation of solutions containing mercury(0) under oxygen free conditions eliminated the oxidation of mercury(0). Solutions of mercury(I) could be quantitatively prepared by the reduction of mercury(II) by mercury(0) under oxygen free conditions.
An ion exchange liquid chromatographic procedure for the separation of the mercury species was studied on both Bio Rad AG 2 X8 and ECTEOLA cellulose Ion exchange materials. Methyl- and phenylmercury(II) chloride were quantitatively separated on the Bio Rad AG 2 X8 resin but the inorganic mercury species were irreversibly absorbed. On the ECTEOLA cellulose polymer mercury(I) and mercury(II) were retained under the same solvent conditions with mercury(I) disproportionating on the column. These ion exchange procedures were of little use for the separation of the inorganic forms of mercury.
Because of the failure of the ion exchange procedures in giving a separation of the inorganic mercury species, an analysis scheme based on selective chemical reactions was studied. This was done in order to develop a means of analyzing a mercury mixture in situ. Mercury(0) could be vaporized from an acid media in the absence of a reducing agent and detected in a UV detection cell. When mercury(I) was also present in the sample, the chloride concentration was adjusted to 0.01M to prevent the disproportionation of mercury(I) from forming additional mercury(0). When care was taken to exclude chloride from a sample of mercury(0) and mercury(I), the mercury(I) was found to quantitatively disproportionate to mercury(0) and mercury(II). The mercury(0) observed was equal to the sum of the quantity of soluble mercury(0) and the quantity of mercury(0) formed by disproportionation. A non-reducing analysis performed in basic media was unsatisfactory for the analysis of inorganic mercury species because of a partial or total reduction of the mercury sample. The inorganic mercury concentration of a sample was determined in a hydrochloric acid-tin(II) media. The total mercury concentration of a sample (including organo mercury) was determined in a basic reducing mixture of tin(II)- and cadmium(II) chloride. The quantity of organic mercury was obtained by subtraction of the analyses in acidic and basic reducing solutions.
The prevention of the disproportionation of mercury (I) by chloride was studied in detail. It was found that -7 a chloride concentration greater than 10 M retarded the disproportionation reaction and a concentration of 0.01M chloride prevented disproportionation during aeration for several hours. The reason for the stability of mercury(I) chloride towards disproportionation was postulated to have been caused by the aging of a colloidal type precipitate.
A mixture of mercury(II) and mercury(I) was analyzed by the addition of a drop of elemental mercury and chloride ions under nitrogen . The increase in concentration of the sample due to the formation of mercury(I), from the reduction of mercury(II) by mercury(0) liquid, was equal to the quantity of mercury(II) in the original sample. The mercury(I) in the sample was quantitated by subtraction of the concentration of mercury(II) from an initial total mercury analysis of the sample.
Hildebrand, David A., "The Differentiation of Mercury Species in Submicrogram Quantities in Aqueous Solution" (1977). Theses and Dissertations. 2770.