Optimisation of an Analytical Technique for Studying 14CH3Hg+ Demethylation Potential
Vesna Jereb
Abstract: Radiotracer I4CHQHg+ is used to follow demethylation products I4CH4 and I4COP which indicate the detoxification mechanisms. In general, two approaches are used to measure COP and CH4: (i) separation of gases on gas chromatoraphy coulmn followed by detection in gas proportional counter or (ii) trapping of products into an appropriate absorption solution followed by liquid scintillation counting (LSC). We prepared a simple system to follow I4CHQHg+ demethylation by using Packard Tri-Carb 2SS0 A/B LSC. The gaseous products from I4CHQHg+ demethylation were trapped in NaOH solution and counted on liquid scintillation counter after the addition of scintillation cocktail. CH4 was combusted to COP in CuO column at high temperature prior to trapping in NaOH solution. Analytical parameters such as counting efficiency, NaOH trapping efficiency, quenching effects, repeatability and limit of detection were determined by varying experimental factors (such as flow of purging gas, concentrations and volumes of NaOH solutions, sample / scintillation cocktail mixing ratios etc.). For this demethylation experiments, soil sample IAEA Soil-I was tested. Sample was spiked with different amounts of I4CHQHg+ radiotracer of high specific activity and incubated in dark for several days at room temperature and under anaerobic conditions. Results of the study suggest reductive demethylation in soil, as the oxidative reductive demethylation potential ratio was about 0.1.
Key words: I4CHQHg demethylation, liquid scintillation counting