Laboratory pH Buffer

• Technical pH buffers:
  This pH buffer solution comes with a certificate from METTLER TOLEDO. Precision is ± 0.02 pH units.
• NIST/DIN pH buffers:
  Buffers prepared according to the recommendation of the National Institute of Standards and Technology (NIST) and the German Institute for Standardization (DIN). They also have a certificate from METTLER TOLEDO. Precision is ± 0.015 pH units.
• Certified pH buffers:
  Selection of pH buffers that are verified and certified by a DAkkS (Deutsche Akkreditierungsstelle, German Accreditation Body) accredited laboratory. Precision is ± 0.02 pH units.

• DIN/NIST pH buffers ± 0.015 pH units
• Certified (DAkkS) pH buffers ± 0.02 pH units
• Technical pH buffers ± 0.02 pH units

*The tolerances are only for the buffer and not for the entire pH measurement of a sample.

The buffers used for calibration must be selected according to the sample's pH. For instance, if a sample is expected to have a pH of 7.45, the calibration must include pH buffers 7.00 and 9.21 (or similar). Use a minimum of two fresh buffers for calibration.

It is not necessary to include pH 7.00 for calibration according to the US and European pharmacopoeia (USP and EP, respectively). But if the calibration is done in compliance with the Japanese Pharmacopoeia (JP), then a pH 6.86 buffer (phosphate) is mandatory. For calibration according to EP, only pH buffer 4.01 (phthalate) is compulsory. If not working according to any regulation, the principle is easy: For calibration, only those pH buffers are needed which bracket the pH range of your samples. For example, in a quality control where every sample should have a pH between 3.5 and 3.8, a two-point calibration with pH 2.00 and 4.01 is sufficient. There is no need for calibration with pH 7.00 in such a case.

The quality of a solution is only guaranteed for unopened bottles that have not yet expired. The following tips will help optimize the use of pH buffer solutions after opening and while in use in the laboratory. Fresh calibration solutions minimize the measurement uncertainty and thus optimize the reproducibility of results:

• Note the date on the bottle when the pH buffer is opened for the first time.
• Keep the bottles sealed tightly at all times and store them at room temperature.
• Never pour dispensed pH buffer solution back into the original bottle.
• Ensure that bottles containing are not contaminated.
• Replace pH buffer solutions that have reached the expiry date or may be contaminated.

The certificates of all calibration solutions and many electrolytes can be downloaded at www.mt.com/buffer. The respective material safety datasheets are available at the same place.

The expiry date indicates the date until which the certificate guarantees the value and the associated measurement uncertainty. After this date the uncertainty cannot be guaranteed. So, it is better to discard expired pH buffer.

Never calibrate directly in the solution bottle. Use a fresh aliquot of pH buffer for each calibration to ensure no contamination enters the bottle.

We offer buffer sachets (small volume packaging of 20mL) that are easy to use and guarantee fresh solutions for every calibration. Each sachet box comes with a printed certificate.

When measuring the pH value of a sample, gently stir the sample to ensure that it is homogeneous. It is important that calibration and measurement are done under the same conditions.

Regular calibrations will lead to more accurate results. Some applications might require a calibration before every measurement, but in general it is enough to calibrate every 24 hours. Always use fresh pH buffers for calibration.