Calibrate a pH meter with bracketing buffers

Practice the USP <791> pH-meter order. Samples are not read until a two-or-more-point calibration brackets the expected pH and an independent check buffer passes.

1. Inspect the electrode.
2. Confirm the fill solution is at the marked level.
3. Calibrate with fresh buffers that bracket the expected sample pH.
4. Rinse between buffers.
5. Allow a stable reading before accepting each point.
6. Verify with an independent check buffer.
7. Measure the sample only after the check is within tolerance.
8. Do not use a one-point “tweak” in place of a failed calibration.