[lylaKuN]

I have one problem about buffer. Note: this is not about how to make buffer, just the phenomenon itself.

We have borate buffer of pH=8.5, if we dilute it more with DI-water,  the pH read by pH meter would not change a lot, almost stay around 8.5, this is reasonable due to the buffering capacity. But if I test the pH of the diluted buffer with pH paper, according to color,  the reading would be much different from 8.5. I'll say it's only around 7.

Does anyone know why it is like this? And which reading (from pH meter or pH paper) is more reliable?

Thank you very much.

[Hunter2]

What kind of pH paper, how old is it, pH paper is only to estimate a pH, the probe is more accurate.