pH buffers & conductivity standards

Calibrate with buffers that bracket the pH you measure. For acidic to neutral samples, a two-point calibration with pH 4 and pH 7 is usual; for neutral to alkaline samples, use pH 7 and pH 10. Always start with pH 7, for example the pH 7.00 buffer, 500 ml, then add the pH 4.01 buffer or the pH 10.00 buffer. If your samples cover a wide range, a three-point calibration with all three gives a better slope across the scale. Your meter's manual tells you which buffer sets it recognises. See also pH meters.

Colour-coded buffers make mix-ups unlikely: in a busy lab you see at once which bottle is which. The pH 4.01 buffer is yellow, the pH 7.00 buffer green and the pH 10.00 buffer blue. Colourless buffers are preferred when a dye could interfere, for instance when the buffer touches samples or when you check the solution visually for contamination. For audited calibrations, certified buffers with a certificate are the usual choice, such as the certified pH 4.01 buffer and the certified pH 7.00 buffer. Questions: sales@luminixhealth.com.

Choose a standard close to the conductivity of your samples, because the cell is most accurate near its calibration point. For drinking water and many process waters, 1413 µS/cm is the common value; it is included in the pH and conductivity calibration set. For low-conductivity water, use a low standard such as the 84 µS/cm standard or the 10 µS/cm standard. For brines, wastewater and concentrated solutions, choose a high standard such as the 12,880 µS/cm standard. Note the reference temperature, usually 25 °C.

The expiry date on the label applies to the closed bottle. Once opened, buffers and standards slowly change: alkaline buffers such as pH 10 absorb carbon dioxide from the air, and low-conductivity standards are easily contaminated. Close the bottle right after use, pour out only what you need and never pour used solution back. Discard it after calibration. Some standards state their shelf life in the title, like the 100 µS/cm calibration standard with a two-year shelf life. Single-use sachets, such as the 12.88 mS/cm standard in sachets, avoid the issue entirely.

A pH buffer for calibration has a stated pH at a stated temperature, often traceable. A conductivity standard has a stated conductivity. They are not general reagents and they should not be poured back into the bottle. The temperature of the measurement has to be the temperature on the label, or the meter has to compensate.

A buffer resists a change in pH when a little acid or base is added. It does that because a weak acid and its conjugate base are both present. A pH buffer used to calibrate a meter has a stated value at a stated temperature. A biological buffer such as Tris or HEPES is chosen because it holds the pH of a living system and does not poison it. Conductivity standards are the sister articles for a conductivity meter. The ions are on PubChem. Electrode calibration practice sits with EURAMET and BELAC.

This shelf belongs to Buffers & pH solutions, inside Lab chemicals. Luminix Health distributes this range for laboratory use.

The neighbouring shelves are Biological buffers (Tris, HEPES, MOPS) and Buffers (other). The category above this shelf is Buffers & pH solutions.

Luminix Health distributes this range from the heart of Europe. We deliver across the EU in two to five days if in stock. Standard delivery is free from €250 excl. VAT. Cold-chain goods and dangerous goods under ADR are never included in that free delivery. The terms are in the Shipping Policy. Send a quote request, contact the team, or read who we are. The full brand index is on shop by brand.

The seven catalogues are Labware, Lab chemicals, Lab instruments, Lab consumables, Chromatography equipment, Lab safety equipment and Life Science & Microbiology. If the article is not on the shelf, request a quote.