If you have checked out the Hanna website, you have seen the wide range of buffer solutions. It depends on your meter, you applications, and your own procedure standards.
General Calibrations
Calibrate to at least two points, always using pH 7.01 and one other point. For around 99% of applications, the general purpose pH 4.01 and pH 7.01 buffer solutions work for you to perform your calibration. For best results, you should make sure you are calibrating using buffers that bracket your sample. pH 7 buffer should always be included to obtain the offset (neutral) point. This means that if your sample is pH 8.6, then pH 7 and pH 10 buffers should be used.
Hanna Tip: Do you have an application where you are testing at the bottom or the top of the pH scale? We have buffers for that! Always make sure to bracket your pH testing range, and custom pH buffers are a way to do it. If you are looking to calibrate to more than two points, some meters are able to calibrate up to five points.
Specialized Calibrations
Another type of pH buffer is a NIST traceable pH buffer. These technical buffers are supplied with a certificate of analysis verifying their NIST traceability. Hanna's technical calibration buffer produced in accordance with ISO 3696/BS3978 standards using high purity salts, deionized water, certified weight-checked balances, and Class A glassware in a temperature controlled environment monitored with certified thermometers. Reported values are accurate to +/- 0.01 pH at 25°C and are traceable to NIST Standard Reference Materials (SRMs).
Another type of pH buffer is a millesiminal buffer. Millesiminal buffers are designed for those who require a resolution of 0.001 for their pH measurements. They are made in accordance with ISO 3696/BS3978 standards using high purity salts, deionized water, certified weight-checked balances, and Class A glassware in a temperature controlled environment monitored with certified thermometers. Reported values are accurate to +/- 0.002 pH @ 25°C and are traceable to NIST Standard Reference Materials (SRMs).