A simple apparatus for measuring the Eh of anaerobic media

A 22-mm outside diameter screw cap test tube was modified for measuring the redox potential (Eh) of samples of anaerobic media. The screw cap was fitted with a grey butyl rubber septum with a hole through which a platinum-calomel combination electrode was inserted. The tube was shortened in length and a small side arm that could be sealed with a serum stopper and an aluminium seal was attached. This device enabled the measurement of Eh of anaerobic media without the need for continuous flushing of the vessel headspace to maintain anaerobiosis.