Is my Iron DTPA solution precipitating or growing a film?

[MusciViridis]

This is my second time making my own Iron DTPA solution and it seems to have precipitated or started growing film suspended in the solution. I threw out the first batch after it started developing the film over several weeks. I made a new one last week and started seeing precipitation/ film after a week. Before making the second batch, I rinsed out the pump bottle with tap water and then with distilled water to prevent this from happening again to no avail. Here's my current procedure:

1. Warm up 250 mL of distilled water in the microwave.
2. Stir in 5 mL of distilled white vinegar (to bring down pH and prevent precipitation in solution).
3. Let the solution sit for a minute.
4. Mix in Fe DTPA 11% powder.
5. Stir until completely dissolved.
6. Pour into a blue opaque pump bottle.
7. Stir it a few more times and let it sit until cool.

I'm seeking guidance on whether there might be an error in my procedure or any preventive measures I can take to avoid this issue from recurring. Any suggestions would be greatly appreciated.

 

[Disaronno]

Potassium sorbate is often added to micro solutions. It's used to inhibit mold and yeast growth. Usually 0.2g per 500mL.

 

[_Maq_]

Have you tried a solution in pure RO water without any additives? What was the result?

 

[Zeus.]

You washed/rinsed out the blue bottle, however you didn't disinfect it first! I use cheap bleach then a good rinse.

 

[John q]

Warm up 250 mL of distilled water in the microwave.
2. Stir in 5 mL of distilled white vinegar (to bring down pH and prevent precipitation in solution).
3. Let the solution sit for a minute.
4. Mix in Fe DTPA 11% powder.
5. Stir until completely disdissolved.

No idea why you are warming the water beforehand, also no idea why you feel the need to acidify said hot water with vinegar.

Mix Fe Dtpa 11% with distilled water, issue resolved.

For everything else there is Barclycard.

BTW: how much FE are you adding to the 250ml of water?

 

[MrClockOff]

You washed/rinsed out the blue bottle, however you didn't disinfect it first! I use cheap bleach then a good rinse.

I love the idea of using bleach for disinfection. Do you neutralise the bleach with Prime and rinse or just rinse before mixing the batch?

 

[_Maq_]

I love the idea of using bleach for disinfection.

What about hydrogen peroxide instead?

 

[Zeus.]

I love the idea of using bleach for disinfection. Do you neutralise the bleach with Prime and rinse or just rinse before mixing the batch?

Well i also use time as i had multiple containers, so would leave them empty dry. But when flushing dosing lines out would use prime after a few rinses.

What about hydrogen peroxide instead?

Not as cheap as bleach and shorter shelf life, plus found peroxide a little tricker to get hold of compared to cheap bleach. Was getting the bleach for about 20 pence a litre.

 

[_Maq_]

I wonder if using boric acid would help. True, we need only very small amount of boron to fertilize, but in stock solution the concentration might be sufficient to protect from any bacteria and fungi. Also, boric acid does not react with most compounds, esp. if pH of the solution is below 9.
The only argument against blending iron chelate with boric acid is that we can overdose iron quite safely but boron we can't.

 

[Happi]

This is my second time making my own Iron DTPA solution and it seems to have precipitated or started growing film suspended in the solution. I threw out the first batch after it started developing the film over several weeks. I made a new one last week and started seeing precipitation/ film after a week. Before making the second batch, I rinsed out the pump bottle with tap water and then with distilled water to prevent this from happening again to no avail. Here's my current procedure:

1. Warm up 250 mL of distilled water in the microwave.
2. Stir in 5 mL of distilled white vinegar (to bring down pH and prevent precipitation in solution).
3. Let the solution sit for a minute.
4. Mix in Fe DTPA 11% powder.
5. Stir until completely dissolved.
6. Pour into a blue opaque pump bottle.
7. Stir it a few more times and let it sit until cool.

I'm seeking guidance on whether there might be an error in my procedure or any preventive measures I can take to avoid this issue from recurring. Any suggestions would be greatly appreciated.

no need to acidify the DTPA Fe 11% Solution, it will drop the PH to 4.0 or so by itself when added to Distilled water (don't use RO water). the only thing you should add is Potassium Sorbate or Sodium Benzoate only if you are planning on keeping and storing this solution for several months.

 

[MusciViridis]

Have you tried a solution in pure RO water without any additives? What was the result?

I haven't tried using pure RO, I opted for distilled based on what is usually recommended when mixing ferts.

No idea why you are warming the water beforehand, also no idea why you feel the need to acidify said hot water with vinegar.

Mix Fe Dtpa 11% with distilled water, issue resolved.

For everything else there is Barclycard.

BTW: how much FE are you adding to the 250ml of water?

I warm the water to aid with solubility and sterilization. And the vinegar is to prevent any mold from growing and to keep the iron from precipitating while in solution. I've heard of others using vinegar as a substitute to potassium sorbate without issues. I'm currently adding 4.73 grams.

You washed/rinsed out the blue bottle, however you didn't disinfect it first! I use cheap bleach then a good rinse.

I'm afraid of using any harsh chemicals even for sterilization purposes to prevent further contamination from traces left behind. I know a good rinse should take care of that, but I just want to minimize introducing anything else that would mess with the integrity of the solution.

 

[_Maq_]

I just want to minimize introducing anything else that would mess with the integrity of the solution.

And yet you add acetic acid.
You don't know what are the possible interactions between acetic acid and iron and DTPA. Do you?
Secondly, vinegar is not exactly pure acetic acid. There are some other organics present in it.
Thirdly, acetic acid, while slightly toxic to microorganisms, is an organic acid, too. Therefore it contains reduced carbon which is the precondition of heterotrophic bacteria and fungi to develop in the first place.

 

[MusciViridis]

And yet you add acetic acid.
You don't know what are the possible interactions between acetic acid and iron and DTPA. Do you?
Secondly, vinegar is not exactly pure acetic acid. There are some other organics present in it.
Thirdly, acetic acid, while slightly toxic to microorganisms, is an organic acid, too. Therefore it contains reduced carbon which is the precondition of heterotrophic bacteria and fungi to develop in the first place.

Correct me if I'm wrong, but isn't there acetic acid in DTPA? Outside of acetic acid and the iron, I don't want any other mineral impurities to affect longevity of the solution.

 

[_Maq_]

isn't there acetic acid in DTPA?

No. These are two very different organic acids.

 

[Happi]

Correct me if I'm wrong, but isn't there acetic acid in DTPA?

I think you are confusing this with Pentetic acid.

 

[MusciViridis]

DTPA aka diethylenetriaminepenta-acetic acid. I'm not here to delve into intricate molecular structures, but rather to discuss the practical aspects. The choice of vinegar stems from its widespread recommendation for mixing chelated iron, as I've previously mentioned. The concern at hand is that some individuals have successfully used vinegar and warm water without experiencing issues like precipitation or the formation of unwanted films in the solution.

 

[Hufsa]

I have not had visible issues with DTPA iron and Acetic Acid (White Vinegar) together.
I would suggest a thorough disinfection of all the containers (with whatever means one finds most appealing), and making sure the tools and procedure is done cleanly and with clean hands. Skip the heating stage unless you have checked its staying below limits for all substances involved. You dont want to heat things beyond their stability.
Potassium sorbate is a standard addition as well. Try not to add too much Acetic Acid, some chelates are not happy in the lowest pH values (below 4.0). 4.25-4.5 pH is what I usually target.

 

[_Maq_]

DTPA aka diethylenetriaminepenta-acetic acid. I'm not here to delve into intricate molecular structures

Take carbon, nitrogen, and potassium. These three are indispensable for life. But one of their compounds - KCN, potassium cyanide - is a killer.
In organic chemistry, the name is composed not from atoms-elements, but rather from groups. DTPA contains ethylene, amine and acetate groups, but this does not make it similar in physico-chemical characteristics to, par example, ethylene, ammonia, or acetic acid.

The choice of vinegar stems from its widespread recommendation for mixing chelated iron

Is it truly widespread? Is it widespread in combination namely with DTPA? (Because "chelated iron" does not indicate that all compounds containing iron in coordinate bond are chemically similar!) Is it really necessary? And, generally speaking, is "widespread" equal to "desirable" or "beneficial"?
@Disaronno and @Happi suggested potassium sorbate. @John q suggested no additives. Me, I consider both these suggestions better than acetic acid ... excuse me, vinegar.

 

[Happi]

some useful Information #17 and #19, the PH drop was quite significant with DTPA Fe 11% hence not requiring the need to acidify the solution with other alternatives.

 

[MusciViridis]

I have not had visible issues with DTPA iron and Acetic Acid (White Vinegar) together.
I would suggest a thorough disinfection of all the containers (with whatever means one finds most appealing), and making sure the tools and procedure is done cleanly and with clean hands. Skip the heating stage unless you have checked its staying below limits for all substances involved. You dont want to heat things beyond their stability.
Potassium sorbate is a standard addition as well. Try not to add too much Acetic Acid, some chelates are not happy in the lowest pH values (below 4.0). 4.25-4.5 pH is what I usually target.

Thank you! This is precisely the guidance I sought – concise and free from unnecessary retorts regarding semantics.