Yesterday I tried to neutralize an O/W emulsion with NaOH 18% to a pH of around 6, quite soon after emulsification. I was about to use sodium ascorbyl phosphate in a predispersion in the cool down, and the SAP needs a pH of about 6.5 to remain stable.
But before I could even get to that (luckily no actives wasted) an ammonia smell came from the emulsion when I mixed the first few drops of NaOH 18%. The temperature was around 38C.
Water, distilled/deionized ad 100
3.0% Betaine (trimethylglycine)
0.1% Dinatrium EDTA
4.5% GMS + PEG-100 Stearate
2.0% Cetyl Alcohol
1.5% Myristyl Myristate
1.0% Shea Butter
3.0% Squalane (olive derived)
5.0% Isoamyl Laurate
1.0% Dimethicon 350 cSt.
0.85% Sepimax Zen
NaOH 18% q.s. pH 6 - 6.5 (the first few drops unto the emulsion at <38C, mixing and => whiff of ammonia
Dissolve individually EDTA, allantoin and finally the betaine. Heat to 70C.
Add individually heat to 70C. Disperse the Zen.
Add B to A while stirring or A to B without stirring. Homogenize.
Dissolve 3,6 grams of NaOH in 16,4 ml/gr water. Let cool down.
q.s. to pH of at least 6
To avoid misunderstandings, I don't mention the cool down phase, as I didn't even get to that. The reason that the Sepimax Zen is so high, is because of the relatively high level of electrolytes I would be adding in the cool down.
The release of ammonia. I don't know why, but I had to think immediately of the allantoin. Which is odd, because I use allantoin all the time and neutralize also many times with NaOH, only not so soon in the process. Or would it be the betaine? I read that betain is a zwitterion and anionic at a pH > 5.5, so no interactions there, or so I hoped.
What would be the culprit for the sudden forming of ammonia?