Inherited one of those pH sticks, sensitive to +/- 0.05, from Whatmann but very much like the pHeps from Hanna. Unfortunately, the two point calibration failed as the buffer 4 was too much out of line to get it working properly (even after a soak for a couple of days). For reference, taking batteries out and in again, buffer 7 read like 6.7, buffer 4 read 5 and buffer 10 read 9.
Soaked it in 3 M KCl (ca. 22.5 g potassium chloride/100ml) for a 2 weeks, the calibration was spot on. Also, without calibration, buffer
7 read actually 7.0, basically saying that the electrode was completely unbiased, or in equilibrium!Will never store my electrodes in anything else anymore!
Before any harrassment starts about sensitivity issues surrounding the use of +/- 0.05 or 0.1 pH pens, I hasten to say that I use the pens only for TA titration of red wines, where I found it hard to determine the end point either blackish or very black.
Rene.