What exactly is a chelating or sequestering ingredient? EDTA binds with metal ions (mostly calcium and iron ions) and keeps them from being reactive with our various ingredients. These metal ions can precipitate in our creations, forming a metallic solid that is really unpleasant. And the metal ions can keep our surfactant mixes from foaming as well as they should, and can remove the scum that builds up on the tub after a bath.
We know auto-oxidation with metals in the oils and water can promote rancidity, so adding EDTA to our creations will bind those metals to the EDTA and slow down the auto-oxidation process. (Which is also another reason to use purified or distilled water - get rid of those naughty metal ions!)
On top of all of this metal binding goodness, EDTA can behave as an auxiliary preservative to kill off those nasty microbes. There's always a chance a beastie will adapt to the preservative in our lotion and learn to live there - eek! - but the chelating agent disrupts the outer lipid layer of the microbes (where stability is calcium and magnesium ion dependent), which increases the penetration of the other anti-microbial preservatives into the bacterial cell!
EDTA is found in a salt form when we buy it from our suppliers - either calcium or sodium - to increase solubility in our creations. It is suggested you use tetrasodium EDTA for alkaline products (pH over 7) and disodium EDTA for products in the pH range of 3.0 to 9.0. We can use it in lotions and surfactant based creations at up to 0.20%, which is enough to do the job (but check your suppliers' recommendations). Add it to your water phase.
Join me tomorrow to see how we can add EDTA to a lotion formula for all that chelating goodness!