Customer Type: All types
Wastewater: All types requiring pH neutralization
Equipment: Pan America Environmental EpH neutralization systems
Pan America Environmental, Inc. provides pH neutralization systems and pH sensor maintenance is frequently required.
pH Electrode Calibration
Since glass pH electrodes measure H+ concentration relative to their reference half-cells, they must be calibrated periodically to ensure accurate, repeatable measurements. Commercial pH calibration buffer solutions are standardized against NIST certified pH references for calibrating meters with resolution up to 0.001 pH.
Although calibration against one pH reference buffer (one-point calibration) typically ensures accurate pH measurement, frequent two-point or even three-point calibrations ensure the most reliable results. Make sure your pH system includes calibration buffers for a range of pH values i.e. 4, 7 & 10.
pH electrodes are shipped with the electrodes moist. Prior to using your electrode for the first time, follow these three steps to condition your electrode:
1. Remove the protective cap or rubber boot from the bottom of the sensor and rinse the electrode with distilled or de-ionized water.
2. Place the electrode in a beaker containing one of the liquids listed below (in order of ionic ability to condition the electrode). Soak for 20 minutes.
• 3.8 M or 4.0 M KCL
• 4.0 pH buffer
• 7.0 pH buffer
Note: Never condition or store a pH electrode in distilled or de-ionized water. Long-term exposure to pure water will damage the special glass membrane due to the water’s ion starved nature.
3. After conditioning the sensor for 20 minutes, rinse the electrode with distilled or de-ionized water. The electrode is now ready for calibration and to measure pH.
Electrodes should be rinsed between samples with distilled or de-ionized water. Never wipe an electrode, wiping can cause erroneous readings due to static charges. Blot the end of the electrode with lint-free paper to remove excess water.
Always keep your pH electrode moist. We recommend that you store your electrode in a solution of 4 M KCl. If 4 M KCl is not available, use a pH 4 or 7 buffer solution. DO NOT store electrode in distilled or de-ionized water—this will cause ions to leach out of the glass bulb and render your electrode useless.
After storage, you may notice white KCl crystals forming outside your electrode. This will not interfere with measurements. Simply rinse the electrode and blot dry before use.
Protective Storage Cap
Most electrodes are shipped with a protective rubber boot over the glass probe to help prevent cracking or scratching. Remove the rubber boot before using your electrode. Keep your electrode in long-term storage with the boot on—just fill the boot with enough 4 M KCl solution to cover the glass bulb and replenish as needed to keep the bulb moist.
pH Temperature Compensation
The pH of any solution is a function of its temperature. Voltage output from the electrode changes linearly in relationship to changes in pH, and the temperature of the solution determines the slope of the graph. One pH unit corresponds to 59.16 mV at 25°C, the standard voltage and temperature to which all calibrations are referenced. The electrode voltage decreases to 54.20 mV/pH unit at 0.0°C and increases to 74.04 mV/pH unit at 100.0°C.
Since pH values are temperature dependent, pH applications require some form of temperature compensation to ensure standardized pH values. Meters and controllers with automatic temperature compensation (ATC) receive a continuous signal from a temperature element and automatically correct the pH value based on the temperature of the solution. Manual temperature compensation requires the user to enter the temperature. ATC is considered to be more practical for most pH applications.
pH measurement is used in a wide variety of applications: agriculture, wastewater treatment, industrial processes, environmental monitoring, and in research and development. pH is a measure of the acidity or alkalinity of a solution. The pH value states the relative quantity of hydrogen ions (H+) contained in a solution. The greater the concentration of H+ the more acidic the solution and the lower the pH. In this relationship, pH is defined as the negative logarithm of hydrogen activity.
A standard pH measuring system consists of three elements:
– pH electrode with or without transmitter for 4-20mA output
– temperature compensation element for ATC
– pH meter, controller or PLC
– EpH Neutralization systems