The HI4016-45 solution is for storage of the FC300B sodium ion selective electrode (ISE). Measurement of sodium in solutions is determined by ion exchange between the selectively permeable glass membrane and the sample solution. The glass sensing membrane must remain hydrated in order to accurately determine sodium concentrations. This solution provides ideal conditions to rehydrate the membrane surface and prepare it for sodium measurements. The HI4016-45 is a 500 mL bottle of storage solution that ensures optimum measurement performance from the FC300B sodium ISE.