Thermo Fisher Scientific C101 Colorimeter - Manual (Page 30)

Measurement: Chlorine Dioxide
C103 Colorimeter
26
Acid to the sample before carrying out the above test procedure. Use a
multiplication factor to correct for the dilution of the sample.
Chlorine:
Chlorine levels greater than 6ppm may interfere. Use two sachets of
Chlorine Dioxide (Glycine) Reagent in step 5) to remove the interference.
Hardness:
No effect at less than 2000ppm CaCO
3
.
Metals and Chlorine in Combination:
If chlorine is present, some metals may interfere with the test. Use two
sachets of Chlorine Dioxide (Glycine) Reagent in step 5) to remove the
interference.
Monochloramine:
Monochloramine will cause a gradual increase in the Chlorine Dioxide
result over time. Take the test result within 1 minute of adding the reagent
sachet to avoid these errors.
Oxidants, including Bromine and Iodine:
These will interfere with the test method at all levels. It is recommended
that an alternative test method is used if these species are present.
Ozone:
May cause interference at levels above 1.5ppm.
Oxidised Manganese or Oxidised Chromium:
All levels will cause interference. To remove this interference:
1. Test a 10ml sample as described in the above procedure.
2. Adjust the pH of a separate 10ml sample to pH6-7 using 1N Sodium
Hydroxide or 1N Sulphuric Acid.
3. Add 1 drop of 20% Potassium Iodide Solution; swirl to mix and then
wait 60 seconds.
4. Add 3 drop of 5g/l Sodium Arsenite Solution and swirl to mix.
5. Use this as the sample in the above test procedure and make a note
of the result. Use a multiplication factor to correct for the dilution of
the sample.