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Buffer and Sample pH Changes
Buffer and sample pH values change with temperature because of
their temperature dependent chemical equilibria. The pH electrode
should be calibrated with buffers that have known pH values at different
temperatures. Buffer values at different temperatures are given in
Table 1.
Orion pH meters automatically calibrate with the correct pH buffer
values based on the measured temperature. All pH meters are unable
to correct sample pH values back to a reference temperature because
every sample has a unique pH value versus temperature relationship.
Therefore, calibration and measurements should be performed at the
same temperature and pH values should be reported with temperature.
Reference Element Drift
Drift can occur when the internal reference elements inside the pH and
reference portions of the electrode are reaching thermal equilibrium
after a temperature change. Long-term drift or slow response can last
until the sample and electrode are at the same temperature.
ROSS electrodes use a unique internal reference to minimize the
equilibration time.
Temperature Sensor Errors
When a pH and ATC probe are placed into a sample that varies
significantly in temperature, the readings can drift for two reasons. First,
the temperature response of the electrode and temperature probe may
not be similar, which prolongs equilibration and drift. Second, a sample
may not have a uniform temperature. Therefore, the pH electrode and
temperature probe are responding to different environments. Stirring
the sample will minimize this effect.
Using LogR technology, Orion V
s
and Orion D
s
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ual
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meters calculate the temperature by measuring the resistance value
of the ROSS pH electrode's sensing bulb. The pH and temperature
response is identical and both measurements occur at the sensing
bulb. Drift is minimized and errors due to environmental differences are
eliminated.
Sure-Flow Electrode Leak Rate
The junction of the ROSS Sure-Flow electrodes has been designed
to leak at a rate of approximately 1 mL per 24 hours. To keep the
junction from clogging, the leak rate is slightly higher than conventional
electrodes. During the average pH measurement time the loss of
fill solution is minimal and the fill solution does not contaminate the
sample.
ROSS Micro pH Electrode
The 8220BNWP ROSS micro pH electrode has been designed to
measure extremely small samples. The measuring tip is 3 mm in
diameter and 40 mm long. The minimum depth of immersion is 4.5 mm
and the minimum sample size is 15 µL in 384 well plates.
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ROSS Ultra, ROSS Ultra Triode and ROSS pH Electrodes
Thermo Scientific Orion
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