Dont Underestimate This Question - What Does DPD#1 Measure?

[dynamictiger]

I think as a lot of people do I understood this question until I thought about some history. And made some enquiries and asked myself a question.

The question I asked is:

If I measure 2 mg/l of chlorine in the pool using DPD#1 then we say we have 2 mg/l of chlorine in the pool.
If I measure 1 mg/l of ozone in the pool using DPD#1 then we would say we have 1 mg/l of ozone in the pool.
However if we measure bromine, and here it depends on test kit, we multiply by 2.2x (2.22 or 2.25) to get the bromine level.
Why?

In looking at this it looks to me like the logic is we are measuring the elemental chlorine and as bromine has a higher molecular weight we multiply to correct. That's sort of logical if we are measuring elemental substance being chlorine or bromine.


However if you look at what the definition of the test is it implies the test is measuring the oxidation of the reagent this is nothing to do with the molecular weight. Am I so wrong in my thinking?