PH Probe Calibration

• PH calculations are based on a line generated when buffers of known pH are measured. By calibrating the pH meters, you are 'telling' the meter where to expect these values and are helping it create the line off which calculations are based. This procedure should be a part of any pH meter training. You can base pH probe calibrations on one, two or three points (although one point calibrations are not recommended unless your measurements closely surround that point).
  
  The buffers represent acidic conditions (which are below seven), basic conditions (those above seven) and circumneutral conditions (those around seven). Usually the buffers used are pH four, pH seven and pH 10. Run through the instruments calibration program once daily (or on each day the probe is used) using these buffering solutions.
  
  

Taking Measurements

• Measuring pH using a probe is a simple exercise that is easy to train someone to do. Insert the probe into the medium you are measuring and wait for the numbers on the display to stabilize. On some instruments, a flashing bar stops flashing when the numbers are ready to read. Most times, however, you can simply wait for the numbers to stop fluctuating to record the value. Some meters have the ability to store values so you can measure many treatments before having to record them. Because pH is temperature dependent, most meters have a thermometer built into the probe so you can also record the temperature (although most meters compensate for temperature differences).
  
  

PH Meter Maintenance

• The probe on the end of the pH meter can be fragile and training on their maintenance is important. Many meters have a hole on the meter itself into which the probe is placed between uses. Other meters have probe covers that fit over the probe. Regardless of where the pH probe is stored, individuals should be trained to always keep the tip of the probe moist, preferably in a solution of 4 Molar potassium chloride. You can store the pH probe in a buffering solution with a pH of four, but do this only temporarily. Take care to rinse the probe with deionized water before and after each use and avoid wiping it with any type of cloth.
  
  

PH Meter Cleaning

• Individuals may need to be trained to clean pH meters that are frequently used. When the bulb on the end of the probe appears hazy, soaking it in a solution of 0.1 Normal hydrochloric acid for 30 minutes will remove the buildup. Make sure to rinse the probe well with deionized water after soaking.
  
  

PH Meter Troubleshooting

• While pH meters vary depending on model, there are a few basic troubleshooting procedures individuals can be trained to go through in the event the meter is nonfunctional. If you receive an error message or the numbers on the meter do not stabilize check the probe to make sure it is not dirty. Some pH probes may need to be refilled with solution, so check the probe to see if the levels of fluid within the probe are low. If the meter will not calibrate, try new buffering solutions. Always check the batteries, even if they are rechargeable.