Importance of pH Testing in Finished Products
DEFINITION OF pH
pH is the measurement of acidity or alkalinity of a solution. It is the negative logarithm of the activity of hydrogen ions (H+). There is an inverse relationship between pH and concentration of H+, therefore when the concentration of H+ ([H+]) is high the pH is low. The pH is expressed as the concentration of [H+] (or acid) and the pH scale ranges from 0 to 14, whereby the lower pH is acidic, 7 is neutral and the higher pH is basic or alkaline.
As the measurement is logarithmic, the slightest change in pH can be significant. 1.0pH unit means the [H+] differs by a factor of 10. Therefore the [H+] at pH 3 is 10 times greater than at pH 4, and 100 times greater than at pH 5.
HOW DO YOU MEASURE pH?
PH can be measured in multiple ways, from the basic pH indicator strips, small pocket and handheld meters, to more comprehensive and accurate bench top meters. Using bench top meters, the pH is determined by measuring the potential difference between 2 electrodes which is analysed with a voltmeter. One of the electrodes is sensitive to [H+] (usually a glass electrode) and the other is a reference electrode (i.e. silver-silver chloride electrode). These electrodes are usually combined into one compact electrode.
WHY SHOULD YOU TEST FOR pH?
In development of a finished product, the pH is carefully considered in order to provide optimal conditions for certain ingredients. In cosmetics, some preservatives and active ingredients may only work or be active at a given pH. For example, enzymes work at a more alkaline pH. Also, the activity of amphoteric surfactants (a compound that can react as either a base or an acid) is dependent on the charge that they acquire, which is based on the pH. This can determine how the surfactants interact with other ingredients.
In developing a new cosmetic, the natural pH of the body must be taken into account. The natural pH of the scalp is slightly acidic whereas the skin is slightly alkaline. In order to maintain the optimal conditions, the pH of a product which is applied to the body must be controlled. In terms of functionality of a product, the pH can be very important. For example, hair dyes are alkaline which helps open the cuticles of the hair, therefore allowing penetration of the dye to the hair follicle. The hair dye conditioner used after the dying process is acidic, causing the cuticles to retract back and for the scalp to return back to a more natural pH.
For safety purposed, it is very important to avoid extremes in pH in order to protect the skin from damage. Extreme pH can damage the skin barrier which can result in transepidermal water loss, meaning that the skin can be more prone to chemical and microbiological attack. Also, a low pH can help reduce the growth of various microorganisms within a product. Some microorganisms can pose a safety risk and can also affect the shelf life and stability of a product.
The level of pH can also affect the organoleptic conditions of a given product. For instance the solubility of ingredients is determined by the pH, which in turn can alter the physical and microbiological stability of the product.
In the hygiene industry, the pH of the product can determine the end use of the finished product. More acidic cleaning products are de-scaling products, toilet cleaner, and sulphuric acid drain cleaners and alkaline products are bleach, ammonia and borax, all of which have completely different applications.
WHAT ARE BENEFITS OF pH TESTING FOR A COMPANY?
It is important for the pH to be analysed prior to authorising release of a batch to the consumer. If a product does not meet the pH specification, which has been carefully decided by the manufacturer, then there is a risk that the product will not perform as expected and as marketed and most importantly, may pose a major safety risk.
pH has an important role to play in various industries including cosmetics and hygiene. Analysis of pH levels is a relatively cheap, quick and effective way to perform a quality control check to see if a certain batch meets the products pH specification. Ultimately, it is one way of ensuring that you as the manufacturer are consistently producing high quality and safe products for your customers.
pH TESTING AT ICNE LTD
Here at ICNE Ltd, we routinely perform pH testing for our customers. The method for pH analysis appears on our UKAS ISO17025 schedule for accreditation and we are also enrolled on the PHARMASSURE proficiency scheme for pH testing, to ensure that our results are compared to a standards’ results. For pH analysis, we use a modified European Pharmacopoeia method, and use a bench top meter, with an accuracy of 0.01 pH units. Our pH meter is calibrated on a daily basis, more so if an extended low or high pH calibration is required. It is calibrated against a range of certified pH buffers covering the full pH scale. For every pH measurement, we perform a quality control check with a buffer of a certified value, and then perform the analysis in duplicate. The calculated uncertainty of our methodology is ± 0.05pH units.