Ordering liquids annoys me, since I always have to pay for shipping. I realized iodophor is sold as a powder, so I decided to make my own. This only makes sense if you want to make several gallons, or if you can get the powder in small quantity.
Note that this is not the same as BTF Iodophor or IO Star. It is more similar to teat dip or Betadine. This sanitizer should be used at pH <= 5.0, while BTF Iodophor supposedly doesn't have that restriction. Fortunately, we can formulate the concentrate to have a low pH even when fully diluted.
Materials needed:
** You want enough surfactant that it can wet plastic and keep it wet, like star san does. You want little enough that it doesn't foam beyond what you can tolerate. You don't want dish soap, because dish soap gets weird when mixed with acid. But you can add dish soap to the sanitizer bucket after you dilute.
Note that this is not the same as BTF Iodophor or IO Star. It is more similar to teat dip or Betadine. This sanitizer should be used at pH <= 5.0, while BTF Iodophor supposedly doesn't have that restriction. Fortunately, we can formulate the concentrate to have a low pH even when fully diluted.
Materials needed:
- ~100 g povodone iodine (PVP-iodine) (iodophor) powder per liter of product. I'm not sure if you can source this from the US. China and India supply it. Taobao even sells it in small quanitities.
- A small amount of citric acid or phosphoric acid.
- Optional: trisodium phosphate, lye, or base that can make a buffer. Only needed if you would like to use the iodophor on skin.
- Strongly recommended: surfactant. More discussion on this to follow.
- Magnetic stir plate and stir bar.
- Stirring spoon to break up clumps.
- I'll make 500 mL of product.
- Set aside 500 mL of (preferably distilled) water.
- Assuming your iodophor powder contains 10% titratable iodine, the standard ratio for this type of product is to mix 10% iodophor into 90% water. Also standard is to mix it a bit stronger to allow for loss of strength. We'll add 10.5%, or 52.5 g of iodophor powder.
- The minimum amount of acid is small, but you absolutely must get the iodophor concentrate to pH=4 or lower, otherwise it is not stable and you will lose iodine.
- Based on an old patent*, the acid amount should be 3-9%. I used too little, and I suspect it didn't work because the powder was already neutralized with something like sodium bicarbonate. If you use citric acid, you will need more than phosphoric acid.
- If you want to be able to use it on skin without worry, make a buffer so the pH will be in the range of 3-5 whether it is in the bottle or diluted for no-rinse use. Again, this is made difficult by the fact that the powder may already be buffered (but not adequately for use after dilution).
- Surfactant: if you have food grade nonionic surfactant (i.e., tween-20 or tween-80), experiment with the amount, but start with 20 grams. You can use others, but use something that's compatible with acid. You can also skip this and add it to your sanitizer bath only when needed.**
- Warm the water to 40-60°C and add most of it to a beaker on a stir plate. Reserve 100 mL for rinsing and to allow for space for the other ingredients.
- Turn on the stir plate.
- Add the acid (or buffer) to the water. Some acid is needed for dissolution and stability, not just sanitizing.
- Add your povidone iodine powder slowly. In my experience, it clumps no matter how you do it, so don't worry too much.
- Leave the stir plate running for half an hour, until the powder dissolves. Use a stir rod to periodically break up clumps and scrape the sides of the beaker.
- If adding surfactant, add it now.
- If the powder isn't dissolved, warm the beaker by putting it in a hot water bath.
- Your iodophor should be dissolved. If not, keep it hot and add water up to 500 mL. When it's dissolved, add water to reach your final volume. Scrape the sides of the beaker with a stirrer or spoon.
- When finished, I like putting it in a mustard squeeze bottle or a contact lens solution bottle. Label it clearly so your hotdog won't end up soaked in iodine.
- Use this iodophor at a rate of 1.25 mL per liter of sanitizer, or at 26 mL (a bit less than 2 TBSP) per 5 gallons.
- The first time you use it, be sure to check the pH to verify it was acidified/buffered correctly. If you did not acidify adequately, you can add some citric acid or vinegar into the sanitizer bucket.
** You want enough surfactant that it can wet plastic and keep it wet, like star san does. You want little enough that it doesn't foam beyond what you can tolerate. You don't want dish soap, because dish soap gets weird when mixed with acid. But you can add dish soap to the sanitizer bucket after you dilute.
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