Campbell Scientific CSIM11 pH and ORP Sensors - Manual (Page 31)

Appendix C. Detailed Calibration
Procedure and Manufacturer Tips
C.1 Calibration
Good laboratory practices should be used and protective
gloves and safety glasses should be worn while handling
any solvents or chemicals. If you are unsure of the proper
technique for handling a chemical or of its hazardous
properties, it is best to discard the electrode eliminating the
risk of danger.
MATERIALS
Buffers
a) 4.01 pH (potassium bipthalate)
b) 7.00 pH (potassium phosphate)
c) 10.00 pH (sodium borate and carbonate)
Thermometer
Beakers
Datalogger programmed to read the pH probe
PROCEDURE
1. Fill beakers with appropriate buffers and continuously measure the
temperature of the buffer in use. If possible, temperature should be at
equilibrium (probe and buffers) before continuing with calibration.
2. Calculate the Nernst temperature compensation for the probe’s current
temperature and adjust the multiplier in the differential voltage instruction
( VoltDiff() in CRBasic or Volt (Diff) (P2) in Edlog) to the appropriate
value. The slope change is usually taken to be –0.2 pH/mV/°C. Examples
of adjusted multipliers would be the multiplicative inverse of the following
slopes: –58 mV/pH at 20 °C, –59 mV/pH at 25 °C, and -60 mV/pH at 30 °C.
3. Zero the pH probe (pH 7 corresponds to 0.0 mV at 25 °C) by placing the
electrode in a 7.0 buffer with the probe connected to the datalogger. Place
the datalogger in real time monitor mode. Electrode should read 7.0 (or
whatever the solution pH should be at the present temperature) ±0.2 pH.
4. Using the offset in the differential voltage instruction ( VoltDiff() or Volt
(Diff) (P2)), adjust the datalogger to read 7.0 pH, or whatever the solution
pH should be at the present temperature.
5. Remove the probe from the pH buffer, rinse the electrode with distilled
water, and place in 4.01 buffer.
6. Place datalogger in real time monitoring mode. The electrode should read
4.01 ±0.2, depending on temperature.
CAUTION
C-1