Avoiding Errors - ProMinent DULCOTEST DT4 Instrucciones De Servicio

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Avoiding errors

Avoiding errors in photometric measurements
1. Vials, caps and stirring rods should be cleaned thoroughly after each analysis to
prevent errors being carried over. Even minor reagent residues can cause errors in
the test results, and, for this reason, the same vial may not be used for the
determination of free and bound chlorine. (DIN 19643-1, 13.6.2).
Use the brush provided for cleaning. If the reacted sample is left to stand for lengthy
periods, tough colour scale can form, and this can be removed using diluted (approx.
4%) hydrochloric acid.
2. The outside of the vial must be clean and dry before starting the analysis. Fingerprints
or droplets of water on the sides of the vial can result in errors. You should therefore
wipe the vial clean using a soft paper tissue (Kleenex, Tempo etc.) prior to
measurement.
3. "Zero calibration" and "Test" must be carried out with the same vial as there may
be slight differences in optical performance between vials.
4. The vials must be positioned in the sample chamber for "Zero calibration" and
"Test" with the graduations ∇ ∆ facing toward the housing mark.
5. "Zero calibration" and "Test" must be carried out with the sample chamber lid
closed.
6. Bubbles on the inside of the vial may also lead to errors. In this case, fit the vial with
a clean cap and remove bubbles by swirling the contents before starting the test.
7. Avoid spillage of water in the sample chamber. If water should leak into the
photometer housing, it can damage electronic components and cause corrosion.
8. Contamination of the windows over the light source and photo sensor in the sample
chamber can result in errors. If this is suspected check the condition of the windows.
Clean using a moist cloth and cotton buds.
9. Use only reagent tablets packed in black printed foil for analyses.
10. The reagent tablets should be added to the water sample directly out of the foil/
bottle without being handled.
11. Large temperature differentials between the photometer, the operating environment
or the sample can lead to incorrect measurement due to, for example, the formation
of condensate in the area of the lens or on the vial.
12. If turbidities appears during the process of colour reaction, this will cause excessive
results. This distortion may frequently be subdued by previously diluting the sample
through oxidation with clear, medium free-water.
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