Quote Originally Posted by albada View Post
I'm suspicious because the pH in the patent is 8.20, but the latest and prior XTOL-batches I've purchased measured 8.29 and 8.26 with a calibrated meter. That makes me suspect the metabisulfite was reduced and/or metaborate was boosted.
Unless less the readings were made close in time to each other and you are skilled and experienced at making precise pH measurements and you have an electrode in excellent condition and calibration solutions that are fresh, I don't take much stock that there is a difference between two pH readings that differ by 0.03 pH units. If those readings were taken on different days, I'd say those readings are equivalent.

I've years of pH experience measuring everything from Deionized water to hazardous wastes, and pH can be a very tricky test for something that appears to be so simple. Something as simple as stirring can have great affect on some types of samples.

I've come to the conclusion that the whole number in a pH reading is pretty reliable. The first decimal can be accurate, but it is sometimes not very precise depending on the sample. The second digit has much less accuracy than the first, but it can be measured well if your setup is good and you have experience making those types of readings. The third digit in a pH reading, except in some special setups, can pretty much be used as a random number generator.

Don't get all uptight about a difference of 0.03 pH units!