• The probe consists of a standard pH electrode that measures the potential drop across a glass membrane. This potential drop is due to a difference in the concentration of hydrogen ion between an interior solution within the probe and the exterior solution, which is the sample. In a pH 7 buffer the probe develops a potential of 1.75 V. The probe shows an approximately 0.25 V increase in potential with each unit decrease in pH, and a 0.25 V decrease in potential with each unit increase in pH.

Auto ID Capable?

• Yes

Calibration

• A standard calibration is loaded with Logger Pro, but for more accurate work you should calibrate the pH probe before use. Use the following procedure to perform a two point calibration:
  • From Logger Pro select Experiment:Calibrate:Pick Sensor.
  • Click on Calibrate Now
  • Rinse the probe's tip with distilled water and place it in a buffer with a pH of near 7 and enter the pH in the appropriate box. Allow the probe's reading to stabilize and click on Keep.
  • Rinse the probe's tip with distilled water and place it in a buffer with a pH of near 4 if you plan to monitor acidic solutions, or a pH of near 10 if you plan to monitor basic solutions. Alow the probe's reading to stabilize and click on Keep.
• Standard buffers with pH values near 4, 7, and 10 are available from the storeroom.

Preparing pH Probe for Use

• Remove the probe from the storage bottle.
• Thoroughly rinse the bottom of the probe (that part immersed in the storage buffer) using deionized water, paying particular attention to the glass bulb.
• Keep probe immersed in solution at times; do not leave probe out in the air!

Maintenance and Storage

• For short term storage (less than 24 hr) the probe can soak in a pH 4 or pH 7 buffer.
• For longer term storage (more than 24 hr) the probe should be immersed in a pH 4 buffer containing 10 g of KCl for every 100 mL of buffer solution.
• Do not store the probe in distilled or deionized water or leave it out in the air.
• If probe is accidentally stored dry, immerse it for a minimum of 8 hours in a pH 4 buffer containing 10 g of KCl for every 100 mL of buffer solution.
• The pH probe can be cleaned, if necessary, by soaking in a light detergent solution. For difficult to remove contamination, soak for 30 sec in 0.1 M HCl and then rinse well with detergent.
• Mold occasionally grows in the storage buffer solution; it will not harm the probe and can be removed with rinsing.

Specifications

• temperature range of 5 to 80 °C
• pH range of 0 - 14 (be cautious about accepting values near these limits)
• precision of ±0.005 pH units
• response time of 1 sec for 90% of final reading
• maximum sampling rate of 4 points/sec; typical rate of 1 point/sec

Chemical Tolerance

• Do not use the probe in solutions containing perchlorate, silver, or sulfide ions.
• Do not use the probe in HF or in strong acid or strong base solutions with concentrations exceeding 1 M
• Solutions of NaOH with concentrations approaching 1 M can be measured, but the probe must not be left in the solution for more than 5 min