I tried to create a suspension of EDTA powder in Glycerin with 1:1 ratio. I keep facing problem of EDTA sedimentation. I've tried other ratios also but this was the only one which formed least amount of sediment.

When I used coarse powder, the sediment formed within 24 hours but when finely ground powder was used, the same occurred but after 3 days. I even tried heating the powder & glycerin together on low & medium heat but EDTA sediment still forms but with varied time.

I'd like that the suspension remain consistent irrespective of how much time goes by. I read on the internet that anti-settling agents (like xanthan gum & microfibrillated cellulose) can be used but I haven't tried that yet.

Can anyone please help & guide me?

  • $\begingroup$ Is shaking/mixing before usage a problem ? There is probably no way but increasing the viscosity, what may affect the medical usage. Sedimentation may be affected by surfactants, but so does the medical usage as well. Mixing is the safest way. $\endgroup$ – Poutnik Jan 14 at 10:36
  • $\begingroup$ Shaking & mixing is quite difficult once the powder settles due to viscosity of the glycerin especially once the mixture is placed in the test tube. $\endgroup$ – Sohail SA Jan 14 at 10:40
  • $\begingroup$ Be aware clarification because of incomplete or missing information means extra effort on both sides. Provide all possibly relevant background when asking. $\endgroup$ – Poutnik Jan 14 at 10:44
  • $\begingroup$ Please, clarify. I've already mentioned all the details in the question... $\endgroup$ – Sohail SA Jan 14 at 10:47
  • $\begingroup$ You have not mentioned there why mixing is not easily applicable. Is applicable reversing orientation during storage ? Any additives may affect the medical application, but you provided no medical context. Somebody may advice the way how to stabilize the suspension, which would work, but would be totally not applicable for the purpose of the suspension. And there is still hanging danger of misguiding with medical consequences, at the edge of being off-topic for this site. $\endgroup$ – Poutnik Jan 14 at 11:06

I see 4 possibilties to avoid EDTA sedimentation:

  1. Mechanical ways like shaking, mixing or container turning - but you say it is not applicable.

  2. Increasing viscosity by thickening glycerol to decrease the rate of sedimentation. Gel stages could probably even stop the sedimentation, but may not be applicable. You may want to try

  3. Other way would have been adjusting the glycerol density to match EDTA density if EDTA had not had too low density $\pu{0.86 g/cm^3}$ ( while glycerol $\pu{1.26 g/cm^3}$). OTOH, if there was a chance to replace glycerol by ethanol 73 w/w %, having the same density as EDTA has ... but I guess there is not.

  4. It may be worthy to try some emulsifiers, but EDTA particles may be too large and emulsifiers may not be applicable for the suspension purpose.

  • Soy lecithin is another emulsifier and thickener
  • Pickering stabilization – uses particles under certain circumstances
  • Sodium phosphates - not directly an emulsifier, but modifies behavior of other molecules, e.g. caesin
  • Mono- and diglycerides - a common emulsifier found in many food products (coffee creamers, ice-creams, spreads, breads, cakes)
  • Sodium stearoyl lactylate
  • DATEM (diacetyl tartaric acid esters of mono- and diglycerides) – an emulsifier used primarily in baking
  • Simple cellulose – a particulate emulsifier derived from plant material using only water
  • $\begingroup$ Thank you for the reply. $\endgroup$ – Sohail SA Jan 15 at 13:07
  • $\begingroup$ Mechanical mixing wasn't an option as after sedimentation EDTA in Glycerol becomes quite hard to mix. $\endgroup$ – Sohail SA Jan 15 at 13:08
  • $\begingroup$ Lowering density was an option but I'm unsure of how that can be achieved? Would appreciate more clarification... $\endgroup$ – Sohail SA Jan 15 at 13:09
  • $\begingroup$ I haven't tried cellulose yet. Will do that & get back to you. But (just a thought) don't you think cellulose won't work as it's water soluble. Will it mix into Glycerol? $\endgroup$ – Sohail SA Jan 15 at 13:11
  • 1
    $\begingroup$ @SohailSA aboue density: You may have noticed the 3rd conditional - a conditional not achivable in past, present or future. The only option would be replacing glycerol by less dense solvent, what is not probably applicable. Celullose is not soluble. You have not commented reversing orientation. $\endgroup$ – Poutnik Jan 15 at 13:12

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