Making Iodiophor solution

I would like to be able to mix random volumes of Iodiophor easily, but I am having a hard time wrapping my head around the 12.5 ppm measurement.

Can anyone tell me where I am going wrong?

As marked on the bottle:
12.5 ppm 1/4 oz per 2.5 gallons
1 tsp per 1.5 gallons

I have a syringe that is marked in mL and a water jug marked in Gallons, so I will be converting to mL/Gallon.

1/4 oz (7.4 mL) in 2.5 gallon = 2.96 mL/gallon
1 tsp (4.9 mL) in 1.5 gallons = 3.3 mL/gallon

Round those two given ratios to 3mL/gallon and that gives 7.92 x 10-4

12.5mL / 1,000,000 mL = 12.5 x 10-6


Are the two concentrations on the bottle not really closer to 8ppm?

p.p.m. = Parts per million = milligrams of soluble substance in each liter of solution

A 12.5 p.p.m solution of Iodophor contains 12.5 milligrams of Iodine in each liter of this solution .

The bottle you have contains a more concentrated solution , therefore it tells you to dilute it to the desired concentration ( p.p.m. ) .

In other words , in order to have a 12.5 p.p.m. solution of Iodophor , you should add 1 tsp of it to 1.5 Gallons of water .

Then you will have a solution which contains 12.5 milligrams of Iodine per liter ( 12.5 p.p.m. ) .

Hector

To continue this line of reasoning:

2.5 gallons is 2.5*3.7854 = 9.4635 liters which at 12.5 ppm implies that it contains 12.5*9.4635 = 118.294 mg of iodine which came from the 1/4 Oz (7.39336 mL) of stock. Conclusion: the concentration of iodine in the stock solution is 118.294/7.39366 = 16 mg/mL.

Thus if you want to make up 5 gallons at 25 ppm you would need 5*3.785*25/16 = 29.57 mL (a bit more than an ounce)

I think we are getting somewhere now. I was neglecting the dilution of the stock solution in my original thoughts. Clearing that up makes it easier to understand.

Is it safe to say that the two ratios listed on the bottle are just 'close enough' quantities? Assuming the 16 mg/mL stock solution -

1/4 oz per 2.5 gallons:
7.39366 mL * 16 mg/mL / 9.4635 L = 12.5 mg/L (ppm)

1 tsp in 1.5 gallons:
4.9 mL * 16 mg/mL / 5.6781 L = 13.8 mg/L (ppm)

Yes, they are clearly just approximate numbers as if you take the 1 tsp/1.5 gal that implies a concentration of the stock of
12.5*1.5*3.7854/5 = 14.1953 mg/mL taking the tsp to be 5 mL which is what one usually sees. This is not the same as 16 mg/L deduced from the 1/4 Oz per 2.5 gallon instruction. One could average the two numbers and round to 15 mg/mL or search the bottle label carefully looking for a concentration information or have a sample titrated in a laboratory. I'd just use the 15 mg/mL and not worry about being terribly accurate.

In fact , you don't have to make an exactly 12.5 p.p.m. solution of Iodophor .

The No-Rinse-Range is 12.5-25 p.p.m.

Hector