Technical note: Total dissolved gas pressure (TDGP) sensing in the laboratory

Abstract

An increasing number of routine laboratory analyses and procedures require the use of gas-free distilled water with a reproducible level of TDGP (1).This proceeds from the need to avoid bubble formation when the water is heated or subjected to lowstrength ultrasonic fields.The use of a simple oxygen sensor (2,3) to provide an estimate of the degree to which distilled water has been degassed can introduce inconsistent results due to different distillation methods,height above sea level,and conditions and duration of storage. As shown by Eaton et al. (4),the degree of deaeration and procedures used to affect it can be a major contributor to such errors in currently used apparatus. Since air is approximately 78% nitrogen and 21% oxygen,a direct measurement of TDGP will give a more complete picture and is obviously preferable.Two recent studies (5,6) have demonstrated the importance of using a consistent TDGP level for reliable comparisons of the results of dissolution studies.The history,applications,and physical embodiment of the method are described.