question about chelating agents and their use and effectiveness

I stumbled on an old discussion post where someone stated that sodium gluconate doesn't function as a chelator at a pH of 5, which is a bit distressing as I not more than 5 mins ago drafted a body wash formula to be set to pH 5 that would use sodium gluconate as my chelator. Can anyone provide insight/clarity on this? I'm not finding much info from my google searches, my searches actually bring up sodium gluconate being effective across a wide pH range. I'm also interested in sodium phytate as it seems like more people on here favour that one, but I have to wait on it to come back in stock on lotioncrafter.

Also, how would I know whether my chelator is actually working effectively or not? Thanks guys.

Comments

  • PharmaPharma Member, Pharmacist
    pKa values will give some indications though, at pH above +/- neutral, metal hydroxide formation starts messing with theory and 1+1=2 logic.
    Most acids only work well in their dissociated (basic) form. Unlike citric and edetic acid, gluconic acid does not just interact with their carboxylates but also with its pH independent hydroxy groups ('good' chelates also contain amine groups which react in an opposite way to pH). Interactions with hydroxyls are quite weak but may still work to a degree; whether or not this suffices remains questionable. I doubt that these metal complexes will be inaccessible to microbes and there's indications (publications) which have me believe that those low pH complexes are even worse regarding fatty acid oxidation than free metals (unless the increased solubility draws them out of the oil phase).
    Phytic acid on the other hand has such low pKa values that it's essentially always deprotonated enough to complex metals even at very low pH whilst it simply precipitates at higher pH (which, from a 'get the metals out of the way' perspective, is the best outcome though might not be from a cosmetic point of view if there's too much deposits).
    Citric acid will not properly work below pH 5 whilst gluconic acid is maybe better than nothing. EDTA as an example has 100 to 1'000 times tighter binding to metal ions at pH 7 compared with pH 5. Unfortunately, there seems to be no useful investigations for poor chelates such as gluconic acid. It's a PITA to find anything useful regarding gluconic acid metal complexes.
  • Thank you veryyyy much. Took a bit of googling but I understand what you're saying, mentioning pKa values was very helpful.

    May I ask, what's your honest take on EDTA vs phytic acid? Or do you prefer some other chelating agent? And let me say I'm not a natural formulator but I'm trying to formulate using more of the "natural alternatives" just for marketing purposes and public perception. Thank you.
  • PerryPerry Administrator, Professional Chemist
    EDTA is the time tested king of chelators in the cosmetic industry.
  • thank you perry, i'll try to get some of that. regarding customer perception, is sodium phytate a suitable chelator?
  • MarkBroussardMarkBroussard Member, Professional Chemist
    @domicanica:

    Tetrasodium Glutamate Diacetatate
    Chemist/Microbiologist formulating in the Organic & Naturals & Clean Beauty arena under ECOCert/Natural Products Assn/Whole Foods/National Organic Program/Clean At Sephora/Credo Clean guidelines focused skincare & haircare products. 

    See website for details www.desertinbloomcosmeticslab.com
  • Thanks Mark. How do you like it as opposed to EDDS?
  • PharmaPharma Member, Pharmacist
    edited April 2021
    From en environmental point of view, EDDS (well, only the S,S-enantiomer) is well biodegradable and probably the only strong chelate which can be produced solely by fermentation (except for phytic acid). However, standard EDDS, to the best of my knowledge, might be the synthetic racemate which isn't that easily biodegradable (same goes for GLDA)... please let me know if you have more insights whether or not the main manufacturers produce pure enatiomers and especially if they do so by fermentation rather than synthesis.
    In theory, EDDS is better suited than GLDA to complex iron at typical pH values of cosmetics (iron chelates commonly refer to Fe3+, however Fe2+ predominates in cosmetics which contain antioxidants) and maybe one of the best regarding copper. On the contrary, EDDS and GLDA are rather weak regarding manganese at a pH below 6. EDTA covers a broader pH range and often has a higher binding affinity. Regarding calcium ions (should you have issues with hard water or think that chelates boost preservation due to complexing calcium quod est demonstrandum): EDTA great, GLDA only at pH >6, EDDS useless. Again, that's just the theory. Manufacturers booklets tell a different story and what the practical outcome in real life is... IDK.
  • Thank you @Pharma. Honestly I think I'm going to have to go back and do more research on chelating and exactly what's taking place chemically to really figure out which one I'd like to use. Or just find a chemist. And like you said, manufacturer booklets tell one story and real life is another. If I had decided to just rely on manufacturer's info and info on repackager's website I'd potentially end up using something ineffective or incompatible with the rest of my ingredients.
  • If you want to use a good chelating agent use EDTA or sodium phytate wich is about 10x more expensive. 
    These two are strong at pH 5.
  • Thanks for your input! How much do I add to formulas and where in the process do I add it in a body lotion and body wash?
  • First thing in the water phase. 
    %0.1 or %0.2. 

    I use %0.2 EDTA in Shampoo
  • GraillotionGraillotion Member
    edited April 2021
    Thanks for your input! How much do I add to formulas and where in the process do I add it in a body lotion and body wash?
    Those are the typical use rates...I suppose I would select the rate based on the quality of water I was starting with.


  • Thanks @Abdullah. @Graillotion, I'm using distilled water so I'm sure 0.1% sodium phytate would be sufficient..
  • Pharma said:
    pKa values will give some indications though, at pH above +/- neutral, metal hydroxide formation starts messing with theory and 1+1=2 logic.
    Most acids only work well in their dissociated (basic) form. Unlike citric and edetic acid, gluconic acid does not just interact with their carboxylates but also with its pH independent hydroxy groups ('good' chelates also contain amine groups which react in an opposite way to pH). Interactions with hydroxyls are quite weak but may still work to a degree; whether or not this suffices remains questionable. I doubt that these metal complexes will be inaccessible to microbes and there's indications (publications) which have me believe that those low pH complexes are even worse regarding fatty acid oxidation than free metals (unless the increased solubility draws them out of the oil phase).
    Phytic acid on the other hand has such low pKa values that it's essentially always deprotonated enough to complex metals even at very low pH whilst it simply precipitates at higher pH (which, from a 'get the metals out of the way' perspective, is the best outcome though might not be from a cosmetic point of view if there's too much deposits).
    Citric acid will not properly work below pH 5 whilst gluconic acid is maybe better than nothing. EDTA as an example has 100 to 1'000 times tighter binding to metal ions at pH 7 compared with pH 5. Unfortunately, there seems to be no useful investigations for poor chelates such as gluconic acid. It's a PITA to find anything useful regarding gluconic acid metal complexes.
    @p@Pharma ;
    1. If we use EDTA at pH 4-4.5, does the chelating power for all metals decrease or it decrease or even don't chelate some metals and don't change for some other metals?

    2. I am currently using 0.2% EDTA in shampoo and lotion both at pH 4-4.5. if EDTA doesn't work well at that pH, should i increase the amount of EDTA so it work better or should i decrease or even not use it because it doesn't work well at that low pH no matter what? 
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