Problems with pH readings all over the place - I think the problem's in the NaCl solution (Aug/14/2009 )
Made a NaCl solution at .29osm/L and tried to pH it like I've done for years and could not get a steady reading at 7.4, but rather at either 5 or 9 pH!!!
Can the plastic bag that the NaCl came out of have leched plasticises into the solution, and can plasticises bind to the junction of the probe?
Two level calibration is working ok?
If you make the solution with pure chemicals and high quality water, there is essentially nothing to buffer the pH. It is not surprising that breathing on it the right way will change the pH dramatically.
try another pH probe and see.