This is another piece of equipment that is essential in cosmetic formulation because pH measurement is a fundamental test in every cosmetic lab. pH is measured not only in the cosmetic industry, but also in many other processes such as environmental monitoring, pharmaceutical manufacturing, scientific research, electronics manufacturing, textile processes, and many others.
WHAT EXACTLY IS PH?
The pH of a medium indicates its acidity, neutrality, or alkalinity. The pH scale has a range of 0 to 14. Acidic substances have a pH less than 7.0, neutral substances have a pH of 7.0, and alkaline substances have a pH greater than 7.0.
WHEN IS IT NOT NECESSARY TO MEASURE PH?
If you're making a water-free product, you don't need to measure pH because oil-based products, such as lip balm don't contain water. Enough water must be present and carry charge in order to measure pH.
WHY IS PH MEASUREMENT NECESSARY?
There are several reasons why knowing the pH of your products is critical.
1. To match the physiological pH of the skin
Except for certain functional or specialty products such as deodorant, hair dye, or chemical peel products, all skincare and haircare products should have a pH between 4.5-6.5.
2. Preservative compatibility
Preservatives are extremely pH dependent. They are effective only within certain pH ranges. You must maintain the pH of your product in order for it to be adequately preserved and safe for consumer use.
3. Compatibility with other ingredients
Some ingredients, such as actives, gums, emulsifiers, or surfactants, require specific pH ranges in order to be biocompatible or bioavailable. In other words, if they are not within the required pH range, they may not function effectively or your product may become unstable.
As a result, the pH plays a critical role in ensuring that your product is chemically and physically stable, with no change in scent, colour, viscosity, or effectiveness throughout its shelf life, and no microbial growth.
Therefore, measuring pH is absolutely essential if you are creating products that require pH adjustment.
TOOLS FOR MEASUREMENT OF PH
1. Making use of a pH chemical indicator.
A chemical indicator has a pH range over which it changes colour at different pH levels. If you want to measure a pH range of 8.2 to 10.0, for example, you will use phenolphthalein (from colourless to pink). When measuring a pH between 6.0 and 7.6, you will use bromothymol blue, which has a colour range of yellow to blue, and litmus indicator, which has a pH range of 4.5 to 8.3 and turns red under acidic conditions and blue under basic conditions.
COMMON ACID-BASE COLOR INDICATORS
2. Using pH Strips or pH Paper
There is a wide range of pH test papers and strips available, ranging from a wide pH range with low sensitivity to a narrow pH range with high sensitivity.
The advantages of using pH strips or papers are as follows:
- faster and easier to use than a pH metre
- portable and simple to store
Using a good quality pH strip can be costly in the long run, especially when compared to the super cheap litmus paper, but I personally find that the convenience outweighs the cost. As a beginner, I strongly advise you to use pH strips. Invest in a pH metre as you progress with your formulation.
I've tried a few brands of pH strips, but the Macherey-Nagel and Mquant non-bleeding pH strips with 88% and 80% accuracy, respectively are the most convenient and provide good results (but of course not within 3 decimal points).
The indicator does not bleed, and the strip can be left in the measurement medium without contaminating it (though I would not recommend doing so). It is available in a variety of pH ranges with varying intervals. The narrower the intervals, the higher the cost and the more accurate the result.
I used three different pH range strips: 0 to 14 (1.0 interval), 0 to 6 (0.5 interval), and 4 to 7 (0.2-0.4 interval). I normally use the 0-14 before adjusting the pH and will use the 4 to 7 as the range narrows.
Of course, there are other brands that provide comparable products.
Some of the pH strips I've used include:
- Lyphan 3.9-6.0 (0.3 interval) - suitable for aqueous products, but the paper is easily broken.
- Aromazone 0-14 (0.5 interval) - not as accurate
- Universal Test Paper 1-14 (1.0 interval) - not as accurate
- Hydrion 0-6.0 (0.5 interval) - adequate for general testing but bleeds.
While pH strips and papers provide greater accuracy and precision than liquid chemical indicators, they fall short of pH metres.
3. The Use of a pH Meter
pH metres are the most accurate type of measurement and are widely used. There are hundreds of them on the market with various features from which to choose. Handheld, portable pH metres are small in comparison to stationary lab applications, benchtop pH metres, which provide more extensive data management.
To begin, get a portable pH metre (I use a Hanna Checker), and as you progress in your formulation, you can always upgrade to a benchtop pH metre. The best pH metre to buy is one with replaceable glass electrodes. Purchase one that can measure not only liquid solutions but also thick cream or solids.
Before investing, conduct research and obtain specifications and recommendations from suppliers, which you can then compare before deciding on the best one for you.
Keep in mind that, while a pH meter is ideal for accurate pH readings, the most important aspect is to keep the electrode moist and clean. It must be calibrated and maintained on a regular basis. To keep your meter in good working order, you'll need a special calibration solutions, a cleaning solution, and a storage solution.
pH Meter requires regular maintenance
So, PH Meter or PH Strips?
Both measure pH, but one is better than the other and one is more expensive than the other. So, which one should you choose? The pH meter is preferred over pH strips because they are more accurate, but pH strips are cheaper for home crafters and beginners. If using pH strips, I recommend getting high quality strips. Never use cheap litmus paper. As you progress, you can consider purchasing a pH meter.
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