Jenway 3540 - Manual (Page 9)

1.6 Good Practice Guidelines – Conductivity
1.
After using the conductivity probe ensure it is rinsed thoroughly, or cleaned then
rinsed if used in adhering samples. Between samples and for short-term storage the
probe should be stored with the measuring plates immersed in a beaker of deionised
water. This should be replaced regularly to ensure no contamination or growth
occurs.
For longer-term storage conductivity probes may be stored dry, but will need soaking
in deionised water for at least 1 hour before re-use.
2. Conductivity measurements are temperature dependent, for greater accuracy and for
measurement comparisons sample temperature must be recorded, along with the
reference temperature and temperature coefficient used.
3.
Calibration against quoted cell constants (K factors) should only be carried out where
these are known and are reliable. If in doubt, good quality calibration standards
should be used for calibration and/or re-calculating the cell constant (K factor).
4. For greatest accuracy in laboratory measurements, and to conform to USP
standards, temperature compensation should be switched off (set temperature
coefficient to zero). In addition, all samples and calibration standards should be kept
at the reference temperature by use of a water bath or other temperature controlled
environment.
5. When measuring samples at a temperature that differs significantly from ambient,
sufficient time must be allowed for the internal temperature sensor to respond to this
change.
6. The presence of particulate matter in the sample can lead to unstable and non-
reproducible results. If necessary filter, or allow the particles to settle prior to
measurement.
7. Ensure no air bubbles are trapped in the measuring cell. Gentle agitation of the cell
should ensure that bubbles are purged.
8. The entire plate area must be immersed in the solution under test. The slots in the
side of the sensor should be below the surface. Ensure the probe is rinsed with
deionised water between each test. A further ‘sample rinse’ may be necessary for low
conductivity measurements.
9. The measurement of low conductivity samples must be performed with great care to
avoid contamination. At the lowest levels the leeching of substances from the sample
container or absorption of gasses from the atmosphere may affect readings.
10. It is advisable to clean the sensor if contamination is evident. This should be
approached in a progressive manner, beginning with deionised water and
progressing to other solvents or a soft airbrush if the deposits persist. The plates can
be damaged and should not come into contact with anything that is likely to abrade
their surface.