What are single and double junction pH probes?
A. The reference cell of a single junction probe has a wick or frit that makes direct contact with the solution being measured. They are easy and fairly cheap to manufacture but contamination occurs faster in a single junction probe and generally last 6 months.
The reference cell of a double junction probe has a wick or frit that makes contact with a second chamber filled with the same material as in the reference cell. This second chamber has a wick or frit that makes direct contact with the solution being measured. Because it has a second chamber, contamination is slowed.
The Bluelab Contact Ring acts as a barrier to the second chamber and is easily cleaned or replaced at a very low cost. The Contact Ring stops contamination getting into the reference cell inside the probe...hence extending it's life. The Bluelab Contact Ring looks like a 'Life Saver' candy so can be thought of as a 'Probe Saver'.
Bluelab Contact Rings are replaced on the Bluelab pH Truncheon every six months but this does depend on what type of solution the pH Truncheon is measuring. The replicable pH probe should last 18 months or more when using the Bluelab Contact Rings.