[Dynamin]

I have a strange problem.  I've made a topical solution containing vitamins, minerals and amino acids.  Whenever I buffer it to PH7, and I then leave it at RT for a day, the PH is somehow magically gone up to around 8.0 or so by the next day.

How can that be??

It cant be the PH meter because whenever I test it on the calibration fluid its spot on.

Is it possible the plastic container is the problem??
Are perhaps plastic molecules seeping into the solution??

I've added an image for reference

[Corribus]

Hard to know without more information on the formulation and what you're buffering with, but vitamins, minerals, and amino acids are often very redox active. They could be reacting with each other, or with oxygen/dissolved CO2.

Plastics are fairly inert, unlikely to be a cause.

[Dynamin]

Hard to know without more information on the formulation and what you're buffering with, but vitamins, minerals, and amino acids are often very redox active. They could be reacting with each other, or with oxygen/dissolved CO2.

Plastics are fairly inert, unlikely to be a cause

Here's more information:

I take a bunch of vitamin, mineral and free-form amino acid pills.  I crush them all up into fine powder, dissolve them in a solution of 50% ethanol and 50% filtered water (Santevia pitcher; PH level 8.5).

I let it sit for a day, I then filter out all the undissolved parts so I have a clear liquid.
I then add white vinegar Q.S. to lower the PH to 7.1 or 7.2.

Everything is working fine up until then.  I then let the solution sit overnight, and the next day the PH level is at 8.0 again.
Very frustrating!!   

[Enthalpy]

The difference between 7 and 8 or 6 is minimal. Very little change in the composition lets the pH drift around 7. From 7 to 8 it would mean adding only 10^-6mol/L of a strong base for instance. Drifting by one unit around 2 or 12 would require a much bigger composition change.

Organic materials react among themselves, from ageing, with air, with light... I feel pretty much normal that the pH drifts.

Imagine that the solution (or suspension?) contains 0.1mol/L of dissociated acids, of which 10ppm react with ethanol over a day, you get already the 10^-6mol/L drift. It's more complicated because these acids aren't fully dissociated, nor can I guess if a reaction with ethanol is the cause, but the idea is that many reasons can let the pH drift around 7, this process is pretty normal, preventing it looks unnecessary and extremely difficult.

[Dynamin]

I think the problem might be that I bought a cheap PH meter: https://www.amazon.ca/gp/product/B01N9R2S35/ref=ppx_yo_dt_b_asin_title_o02__o00_s00?ie=UTF8&psc=1

I'm gonna go out tomorrow and buy a better one

[Dynamin]

Okay, so I bought a better PH meter and the solution is still going up to PH8 whenever I bring it down to PH7.
The reason why it must be PH7 is because the vitamin solution wont be absorbed well by the skin if its not at PH7.

Is there anything I can do to the solution to keep it reasonably stable at PH7??
A fluctuation of .2 to .3 points is okay, but not more then that

[jeffmoonchop]

try using phosphates or citrates to buffer it. ethanol affects apparent pH reading. In my experience, it gives a higher value. if you use pH 7 phosphate buffer instead of water it might stabilise the pH.

[Dynamin]

try using phosphates or citrates to buffer it. ethanol affects apparent pH reading. In my experience, it gives a higher value. if you use pH 7 phosphate buffer instead of water it might stabilise the pH

Would using iso-propyl alcohol as a solvent instead of ethanol solve the problem??