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Use the up/down keys to adjust the values to match
the certificates, following the order defined on the
display. Press OK when the correct value is shown
and the prompt will forward to the next value.
Upon completion the message Check Standard
Values assigned successfully will be displayed.
Press OK to return to the Check Standard Mode menu.
Check Standard Measurement
Follow the on-screen prompts to insert the Check
Standards in the defined order. The Photometer
7500 will automatically measure the
Transmittance at the required wavelength.
Upon completion of the sequence the results are
displayed on screen with pass or fail status.
If the Check Standard Mode reports a failure,
see Section 3.9 Troubleshooting for guidance or
contact your local Palintest supplier.
3.8 Photometric Testing Hints and Tips
Photometric analysis is a very powerful technique,
providing accurate analysis of a wide range
of critical drinking water, wastewater and
environmental parameters.
Palintest has focused on simplifying the test
methods and equipment used for this technique
but there are still a number of ways to ensure the
results you generate are as accurate as possible:
Photometer 7500
1 Always use genuine Palintest reagents when
using the programmed test methods. Each
parameter has a unique calibration which
has been generated using Palintest reagents.
Alternative reagents may follow the same
general methodology but can differ
substantially in formulation and colour
generated thereby rendering the calibration
and hence results inaccurate.
2 Always correct for the blank value - any
inherent colour in the sample (which may not
be visible to the naked eye) will offset the
result if the blank step is omitted. If the sample
colour is too intense for the photometer to
blank use dilution with deionised water to
reduce the intensity. Remember to dilute the
sample to the same extent for analysis.
3 Always respect the reaction time specified
within the instructions. Some methods
produce instant colour whereas others require
a reaction time to reach full development.
Taking a reading before the reaction time
has elapsed may lead to low results.
4 The presence of solids, either large or in the
form of turbidity, can adversely affect the
quality of results by preventing incident light
from reaching the detector. The blanking step
can reduce the impact of turbidity interference
but large solid particles must be removed prior
to analysis. Solids can be removed by filtration
prior to analysis or, if the solids are settleable
and will not lie in the optical path, allowing
them to settle in the photometer cuvette can
be acceptable.
5 Calibration curves relate transmission/
absorbance to concentration to provide result
data but not all calibration ranges are linear.
Frequently at higher concentrations the curve
'flattens' leading to higher potential variability
in results. If greater accuracy is required than
can be achieved on neat samples then dilution
can be used to improve performance.
6 Ensure the photometer cuvette is clean, has
no droplets on the outside and not excessively
scratched. Good technique is to wipe the outside
surface of the cuvette prior to inserting into
the optical chamber to prevent contamination
of the optical system.
7 Always use good quality, genuine Palintest
cuvettes. Use the orientation mark to ensure
repeatable positioning of the cuvette.
3
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