Chelating agents comparison

According to this chart that compares chelating agents, can %0.3 citric acid be as effective as %0.1 EDTA? 
If not then at what percentage citric acid would be a good replacement for %0.1 EDTA?


  • PharmaPharma Member, Pharmacist
    More chelate doesn't actually mean a better action. Furthermore, apparent binding affinity depends on ionic strength of the medium, temperature and more importantly pH. Bear in mind that binding is reversible, free and bound metal are in equilibrium which means that said numbers refer to the ratio of bound versus free metal ions.
    But the most important thing to note is that the K numbers in that chart (stability constants, more correctly pK values) are log-scale, not linear. The metals of concern in a cosmetic product are usually Cu, Fe, and Mn with Ca only in certain products.
    Let's take iron as an example and do simple 1+1=2 maths and ignore concentration effects and the rest: 25.1 v.s. 11.2 means a difference of roughly 14. To obtain the same amount of bound iron with citrate than EDTA, you'd have to take about 100'000'000'000'000 times more citrate than EDTA!
    I guess that should suffice as an answer ;) .
  • @Pharma that was a wonderful explanation 👏. I will not think of citrate as an alternative to EDTA anymore.

    Another question:
    If Cu, Fe and Mn are the metals of concern in cosmetic, according to the chart above EDTA is a lot more stronger than GLDA but the chart below shows GLDA functions better than EDTA at same quantity. Any thoughts on this?
    The chart below is from supplier. 
  • PharmaPharma Member, Pharmacist
    GLDA is about 10% heavier than EDTA and the graph would look even more extreme were it in mM instead of ppm ;) .
    Anyway, such differences are not only due to binding affinities but a several other factors such as pH dependence, solubility of free and complexed chelates, assimilation, cell wall interactions, biodegradation, competition with microbial sequestrants, and non-chelate effects.
    Overall, the graph is biased because it highlights the very narrow range of 1000 to 1400 ppm where there are differences. Besides that, it's a very non-self-explanatory graph with chelate concentration on the x-axis and quaternary ammonium compound on the y-axis. Whatever that means... Maybe the effect (whatever effect that is, it's not mentioned) is caused by precipitation of QAC-chelate salts?
  • PerryPerry Administrator, Professional Chemist
    @Pharma - Raw material supplier being misleading!?  Say it ain't so!

    This is a good lesson for everyone though. Raw material supplier data should always be viewed skeptically. Not saying that they outright lie, but they certainly present the data in a way that is more favorable to getting you to come to the conclusions they want. 

  • PharmaPharma Member, Pharmacist
    GLDA has one huge advantage over EDTA: It's biodegradable, not super fast and only after acclimatisation of or inoculation with corresponding microbes but that's already better than EDTA. On the up-side, GLDA's not so good chelating power makes bound metal plant available. In hydroponics and agriculture but also when accumulating in nature, this is a huge plus point. Synthesis-wise, it can be obtained more readily from renewable resources with less dependence on petroleum chemistry and, given that it is intended as more eco-friendly alternative to EDTA, a greener production chemistry is part of the sales pitch. On the down side, EDTA just works better and more efficient in a cosmetic product (if you're the the type of 'screw Greta, climate change is a problem the next generation should deal with' person, EDTA is sadly still the way to go if you want to go better safe than sorry).
  • @Perry thanks. 
  • @Pharma that is cool 😎.

    So is biodegradability the only problem with EDTA or it has any negative effect for consumer too like irritation or when absorbed from leave on product, when used at %0.1-0.2?
  • RedCoastRedCoast Member
    edited March 2021
    Disodium EDTA has only had a few incidences of allergic contact dermatitis in scientific literature. Considering how ubiquitous that chelator is, allergies to it appear to be exceptionally rare. One study that reported allergies to ETDA involved a 1% concentration, which is far higher than any cosmetic ingredient would ever use.

    In other words, wouldn't worry about those "side effects".

    But yeah, most of the criticism with disodium EDTA is its lack of biodegradability and its potential harm to aquatic wildlife.
  • @RedCoast thanks 😊
  • PharmaPharma Member, Pharmacist
    There are hypothetical concerns that EDTA might actually shuttle heavy metal contaminants through skin... in cases where this might be true (injured skin) it will be as true for other chelates as well. So, the only concern is its effects on the environment.
  • what about the performance of sodium phytate compared with EDTA? any evidence??
    Dr. Catherine Pratt
    (B.Sc with HONS I , Ph.D Analytical/Organic Chem and Microbiology), Cosmetic Chemistry IPCS)
  • @Dr Catherine Pratt have a look at this
  • @Pharma thanks
  • PharmaPharma Member, Pharmacist
    A HUGE advantage of phytic acid over carbonic acid based chelates is it's efficacy at low pH. A lot of things I found on chelates come from industrial applications where pH is often neutral to alkaline.
    The downside can be that this little molecule may carry up to 12 negative charges.
  • @Pharma does it mean it is not compatible with cationics? 
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