This is the summary of how to test a lotion with a pH meter!
- Remove 5 grams from your emulsion master batch. Weigh 5 grams of the emulsion into a container, then add 95 grams distilled water. Mix until it’s all dissolved and uniform. We can call this the emulsion sample, emulsion solution, or diluted emulsion solution.
- Measure the pH by placing your meter in the emulsion sample, then swish it around to get rid of any air bubbles. Leave it for the suggested time to get a good reading, usually 30 seconds to 1 minute.
- Write down this number before adjusting the pH with either an acid or alkaline ingredient. This is the pH of the emulsion. Also write down the temperature as the pH can alter with the temperature.
- If you want to reduce the pH, add 0.1% grams of a 50/50 solution of citric acid/distilled water into the container, mix well, then follow the above process to test the pH. Add 0.1% solution into the sample, mix well, then test until you arrive at the pH you want.
- If you want to increase the pH, add 0.1% grams of an 18% diluted lye sample or triethanolamine to the sample container, mix well, then follow the above process to test the pH. Add 0.1% solution into the sample, mix well, then test until you arrive at the pH you want.
- Add the same percentage of the pH adjusting solution to the emulsion master batch, mix as suggested, then remove a sample to test the pH. If it is the pH you want, you’re done. If not, follow this process again until you reach the target pH.
- Write all of this down so when you make the emulsion again, you can add this amount of pH adjusting solution to the appropriate phase to get a similar pH.
- Please note, if you change any of the water soluble or emulsifying ingredients in the formula, you will need to test the pH again and follow this process as this can alter the pH of the entire product.
If you’d like to read a longer post, you can find it here – Tips & techniques: Testing and adjusting the pH of a emulsion with a pH meter
If you’d like to read a longer post with more science-y goodness, you can find it here – Acids, bases, and pH – oh my! Part four: Testing our products with pH meters!
If you want to learn even more about pH and pH meters, I have a huge section that you can find under the cosmetic chemistry concepts of the site, always found under the “resources” tab in the menu bar. Click the link, then then link for the series on pH in that section in the table of contents.