The performance of the open system (Bethge's apparatus) of digestion of biological materials for mercury analysis has been upgraded to compare favourably with the closed systems. Losses at the joints and during refluxing were successfully eliminated by the following modifications: (i) thin PTFE cylinders were used in the joints; (ii) a PTFE two-way stopper was used instead of the glass stopper in the original apparatus; (iii) a double-faced spiral condenser was used to increase the cooling efficiency and minimise losses.
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