Hydrogen ion buffers comprising a mixture of a weak acid and its conjugate base or vice-versa and used to stabilize pH; also diluents, washing solutions, and standard-value solutions used for a broad array of scientific calibration purposes.

The buffers used to calibrate pH meters may be certified and/or traceable to the National Institute of Standards and Technology (NIST). These buffers may also be color-coded for easy identification:

• Red: pH 4.0
• Yellow: pH 7.0
• Blue: pH 10.0