12
The sensitive glass bulb at the front of the combination electrode should not come in contact with hard
surfaces. Scratches or cracks on the electrode will cause inaccurate readings. Before and after each
measurement, wash the electrode with pure water and then throw off the excess water on the electrode. Do
not clean the glass bulb with a tissue for it will affect the stability of the electrode potential and increase the
response time. The electrode should be thoroughly cleaned if a sample sticks to the electrode. Use a solvent
if the solution does not appear clean after washing.
4.6.4. Renew glass bulb
Electrodes that have been used over a long period of time, will become aged. Submerge the electrode in 0.1
mol/L hydrochloric acid for 24 hours, then wash the electrode in pure water, then submerge it in soaking
solution for 24 hours. The method to prepare 0.1mol/L hydrochloric acid: dilute 9mL hydrochloric acid in pure
water to 1000mL. For serious passivation, submerge the bulb in 4% HF (hydrofluoric acid) for 3-5 seconds,
and wash it in pure water, then submerge it in the soaking solution for 24 hours to renew it.)
4.6.5. Clean contaminated glass bulb and junction (see Chart
– 7)
Chart
– 7 Clean contaminated glass bulb and junction
Contamination
Cleaning Solutions
Inorganic metal oxide
Dilute acid less than 1mol/L
Organic lipid
Dilute detergent (weak alkaline)
Resin macromolecule
Dilute alcohol, acetone, ether
Proteinic haematocyte sediment
Acidic enzymatic solution (saccharated yeast tablets)
Paints
Dilute bleacher, peroxide
Notes:
The electrode housing is polycarbonate. When using cleaning solutions, take precautions with
carbon tetrachloride, trichlorethylene, tetrahydrofuran, acetone, etc, as these will dissolve the
housing and invalidate the electrode.
5. mV Measurement:
5.1.
Press key, and switch the meter to mV measurement mode. Connect ORP electrode (purchased
separately) and dip it in sample solution, stir the solution briefly and allow it to stay in the solution until
icon appears and get the reading which is ORP value.ORP means Oxidation Reduction Potential. The unit is
mV.
5.2. Notes:
5.2.1.
ORP measurement does not require calibration. When the user is not sure about ORP electrode
quality or measuring value, use ORP standard solution to test mV value and see whether ORP electrode or
meter works properly.
5.2.2. Clean and activate ORP electrode
After the electrode has been used over long period of time, the platinum surface will get contaminated and
will lead to inaccurate measurements and slow responses. Please refer to the following methods to clean and
activate ORP electrode:
