Electro-Chemical Devices (ECD) SMS22 - Manual (Page 29)

If possible, the electrode should be cleaned without removing it from the sensor body. However, if the
electrode must be removed, the o-rings must be inspected and re-lubricated.
Remove the pH sensor from the flow cell and carefully wash the wetted end of the electrode cartridge
in a mild solution of detergent and water or with isopropyl alcohol. If the electrode response is not
improved, soak the electrode in 0.1 Molar HCl for 5 minutes. Remove and rinse the electrode with tap
water and soak in 0.1 Molar NaOH for 5 minutes.
Remove the electrode from the NaOH solution, rinse the electrode and soak in a 4 pH buffer solution for
10 minutes. This should improve the response of the electrode. If not, replace the electrode.
If the electrode must be left out of the process for an extended period of time, store it in a solution of
water saturated with KCl or a 4.0 pH buffer solution. ECD does not recommend the storage of electrodes
in distilled or deionized water.
Ion selective electrodes require periodic service. Weekly checks should be performed to assure the
accuracy of the measurement.
The ion selective crystal that senses the ion concentration can become sluggish in response due to
coating or reactions with the process solution. Periodic cleaning or polishing will minimize drift and
maintain the sensors response.
CLEANING
The solid state crystal based sulfide electrodes are fairly robust and can be cleaned with alcohols,
detergents or dilute acids to remove coatings caused by greases, oils or films. A soft tooth brush or
paper towel should be used to remove stubborn coatings. Do not clean with a wire brush. Metal
carryover from the brush will compromise the measurement. Cleaning should be followed by polishing
before calibrating the sensor.
POLISHING
Abrasive polishing is only recommended for the solid state crystal style Combination Electrodes. ECD
supplies two styles of abrasive cleaning kits, a package of light blue colored polishing strips or a small
vial of alumina powder with a felt polishing pad.
The sensing surface of solid state electrodes can wear over time, which causes drift, poor reproducibility
and loss of response in low level samples. The electrode can be restored by polishing the sensing surface
with a polishing kit. The polishing kit can also be used if the sensing surface has been etched or
chemically poisoned.
a. Place a small amount of the alumina polishing powder near one of the edges of the
polishing pad or use the blue polishing strip.
b. Place a few drops of distilled water on the pad to wet the powder or strip.
c. Hold the electrode with the sensing surface facing down on the wetted polishing
pad/powder.
d. Slide the electrode back and forth across the pad, the sensing tip will be abraded and a
new electrode surface will be generated.
SMS-22 Page 20