The measurement of pH in water demands high accuracy since sea water has a high ionic strength and is weakly buffered. The pH range in seawater is particularly restricted and, only in very special cases, the observed values are outside the range of 6.5 to 9.0 pH.
Some problems have always arisen from the use of traditional reference sensors with porous diaphragms, when measuring the pH in sea water, in particular at pressures in excess of a few bar, due to the high and variable junction potentials which are generated. The pH sensors have titanium body and a pH sensitive glass tip which can withstand pressures up to 150 bar and 700 bar.
