Specifications
Storage/Shelf Life
pH electrodes have a limited shelf life. Therefore, it is important to have
a backup electrode. It is important to ensure that the spare electrode is
in working condition when required. Electrodes supplied with soaker
storage bottles with special soaker solutions have longer shelf life than
those supplied dry with small caps.
Most Eutech pH electrodes are supplied with storage solutions for
extended electrode life.
A dry or dehydrated electrode membrane will not respond properly to
changes in acidity. The special solution in soaker bottles provides an
environment that maintains pH glass hydration in an acidic environment
and keeps the reference junction wet. If the original solution is no longer
available, the following are acceptable storage media for pH electrodes
in order of preference:
• 4.00 pH Buer • 7.00 pH Buer
Other pH buers or tap water are also acceptable storage media, but
avoid storage in deionised water.
Note: When pH electrodes are stored in deionised water, ions
from pH glass membranes and reference junction solution are
consumed by the deionised water. Deionized water should only
be used for rinsing.
Electrode Maintenance
pH electrodes are susceptible to dirt and contamination and need to be
cleaned regularly depending on the extent and condition of use. Wash
the electrode and reference junction quickly in deionised water. Close
the relling hole by returning its rubber sleeve or stopper cap (necessary
for only rellable electrodes). Store the electrode as mentioned above,
or as recommended by the manufacturer.
Electrolyte Replacement (For Rellable Electrodes only)
The reference electrolyte needs to be relled when the electrode has
been used for an extended period, or when the internal electrolyte has
dried up. The old reference electrolyte can be removed with a syringe
and a exible tube and replaced with a fresh electrolyte as recommended
for the electrode.
Electrode Cleaning
Electrodes that are mechanically intact can be restored to normal
performance by the following procedures.
a Salt Deposits
Dissolve the deposit by immersing the electrode in tap water for 10
to 15 minutes. Then rinse with deionised water.
b Oil/Grease Films
Wash electrode pH glass in a little detergent and water. Rinse electrode
tip with deionised water.
c Clogged Reference Junction
Heat a dilute KCl solution to 60 - 80 °C. Place the sensing portion
of the pH electrode into the heated KCl solution for approximately
10 minutes. Allow the electrode to cool while immersed in pH 4.01
buer solution.
d Protein Deposits
Prepare a 1 % pepsin solution in 0.1M HCl. Allow the electrode to
stand in this solution for ve to ten minutes. Rinse the electrode with
deionised water.
About ORP Measurement
ORP – Oxidation Reduction Potential
Oxidation-Reduction Potential (ORP) or Redox Potential measurements
are used to monitor chemical reactions, to quantify ion activity, or to
determine the oxidizing or reducing properties of a solution. ORP is a
measurement of the electrical potential of a redox reaction and serves
as a yardstick to judge how much oxidation or reduction takes place
under existing conditions.
ORP electrodes measure the voltage across a circuit formed by the
measuring metal half cell and the reference half cell. When the ORP
electrode is placed in the presence of oxidizing or reducing agents,
electrons are constantly transferred back and forth on its measuring
surface, generating a tiny voltage. The ORP measurement can be made
using the millivolt mode of a pH meter.
Major areas of usage include the treatment of industrial wastes, study of
biological systems, oxidation of cyanide, bleaching of pulp, manufacture
of bleach and reduction of chromate wastes.
The measurement of ORP is also useful in pool water treatment as
an indication of sanitation in relation to free chlorine parameter. ORP
technology has gained recognition worldwide and is found to be a
reliable indicator of bacteriological water quality. The table below
illustrates the Kill Time of E.Coli bacteria as a function of ORP value. With
a value of 600 mV, the life of the bacteria is almost 2 minutes; at 650 mV
it reduces to 30 seconds. Above 700 mV the bacteria is killed within a
few seconds. It is therefore necessary for the water to have an ORP value
of at least 700 mV to ensure good water quality.
ORP value also depends on the pH of pool water. Normal values lie
between 7.2 and 7.6 pH with a tendency to increase to around 8.0 to 9.0
pH depending on the level of contamination. The pH of the pool water
has to be maintained at the optimum level between 7.2 and 7.6 pH by
dosing appropriate chemicals. If the pH of the swimming pool water is
acceptable and the ORP value is below 700 mV, hypochlorite or other
oxidising chemicals should be added.
Eutech oers a wide range of meters that measure both pH and
ORP values in various educational, laboratory and industrial
applications. These include ORPTestr™ 10 pocket tester, handheld
meters CyberScan Series pH 300, pH 310, pH 11 and pH 110, EcoScan
pH 6 and the CyberScan bench meter series 510, 1100, 2100, 1500
and the colour touchscreen research-grade series 6000.
pH/ORP | About pH/ORP Measurement
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