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1. Response to ban on O.T.

Dear Sirs,

As far as water testing is concerned, we have not come across any communication regarding ban on Orthotolidine for Chlorine Testing.

We are manufacturers of Water Testing Kits since 1985 and manufacture following products for testing of Residual Chlorine:

  1. Chlorine Test Kit (based on Orthotolidine)
  2. Chlorine Test Kit (based on DPD Tablets) - Probably the only Indian manufacturer of DPD Tablets / DPD Tablet based Kits in India
  3. On-line Automatic Chlorine Analyser (First time in India)

While on the subject, I would like to mention some other related aspects to Orthotolidine issue:

a)      Orthotolidine is a known carcinogenic chemical.  However, for testing of Chlorine, quantity of Orthotolidine required is only about 0.3 to 0.4 mg. per test. Hence, in view of the minute quantity that is used in each testing (and quantity that the user is likely to be exposed to), it is felt, the issue of it being harmful is a bit far-fetched. Ban on its use in Chlorine testing may not be a correct approach. Caution while using (and not ban) may be the right approach, in view of utility and simplicity of the OT based Chlorine test.

b)      On the flipside, there is another aspect. The simple OT based test that is used all over India, measures Total Residual Chlorine (TRC). The Indian Standard for drinking water IS:10500 specifies limit for Chlorine as 0.2 ppm minimum Free Residual Chlorine (FRC). FRC can be measured conveniently by DPD method only. Hence, if Indian Standard is to be followed to the word, we should use DPD method for testing Chlorine. With DPD method, it is possible to measure both FRC, as well as, TRC easily and quickly.


Ravi Savant,

Prerana Laboratories, Prerana House, Near Chhatrapati Bank, Vishal Nagar, Jagtap Dairy, Aundh-Wakad Road, Pune – 411 027.

Tel: 020 27274958, 9371015199



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