How to measure water activity in pharmaceutical manufacturing

water activiy measurement pharmaceutical

Which is the best aw measurement instrument to choose?

The accurate measurement of water activity is an important quality control procedure for a wide range of pharmaceutical manufacturing processes. In particular, by determining the exact level of water activity (aw) you can assess the risk of microbial growth in non-sterile dosage products. Water activity also allows potential changes in the physical characteristics of products, such as disintegration, swelling and caking of powdered pharmaceuticals, to be predicted. Ultimately, aw is a valuable measurement that can be used as part of the control procedures to ensure compliance with various regulatory requirements.

It is worth noting that the value of aw measurement is reflected in the latest version of the US Pharmacopeia (USP). This highlights that where suitable risk assessments have been carried out, and where products are proven to have a low level of water activity, it may be unnecessary to carry out further and often costly microbial testing.

How to measure aw

Most water activity measurements are taken using either laboratory or portable instruments. In each case the procedure involves extracting a sample of the product to be measured. It is important to ensure that the sample is prepared to eliminate the risk of contamination, also to note that water activity is sensitive to temperature, so a stable measurement environment must be maintained.

The sample is first placed in a disposable sample cup, designed for liquids, powders or solids. This should be left until the temperature of the sample matches that of the probe – normally ambient temperature; it is a common mistake to take samples either directly from storage in a fridge or from a hot manufacturing process. An alternative is to control both sample and probe at a constant temperature.

Once temperatures have stabilized then the sample can be entered into the water activity instrument. After a short interval – typically just a few minutes – the instrument will automatically calculate aw levels, based on either a predictive model embedded in the system software, or by waiting until the water vapor pressure and temperature have reached equilibrium within the measurement chamber.

It’s a quick and simple process. For a more detailed explanation, please read our blog post: How to carry out a Water Activity (aw) Measurement

The best instruments for measuring water activity

It should go without saying that the best instruments for measuring water activity must be highly accurate, reliable and easy to use. Additionally, that portable instruments should be robust, compact and lightweight, with fast response and digital output options for ease of data capture, logging and traceability. Instrumentation alone, however, is not sufficient. It is also vital to ensure that users have a good understanding of water activity theory, instrument best practice and guidance for use within a compliant process.

At PST, we offer Rotronic’s range of dedicated water activity probes, meters and analyzers, for both spot and laboratory measurements. These devices offer a choice of options, including and excluding integrated temperature control.

At the heart of each instrument is an advanced capacitive humidity sensor, with a hygroscopic polymer dielectric material sandwiched between two porous platinum electrodes. This construction is extremely stable and reliable, ensuring excellent hysteresis, linearity and temperature stability under a variety of operating conditions. The nature of the sensor is, however, just one aspect of overall system accuracy. Equally important is the functionality and performance of the mechanical components, associated electronics and instrument calibration.

Take a detailed look at our capacitive sensor technology.

Among the best examples of water activity instruments are our AwEasy (without temperature control) and AwTherm (with temperature control), which are designed to offer a unique combination of precision, reliability and ease of use. These benefits are further enhanced by our sophisticated AwEasy app for Android and iOS, and our HygroSoft laboratory software for Windows PCs. These software options make water activity analysis, reporting and traceability quick and simple, while offering the ability to control meters and probes remotely.

To learn more about our range of products for measuring water activity please follow this link.

We are the world’s leading experts in water activity, moisture monitoring and Dew Point measurement. We have eight different technologies covering all moisture applications, backed by unrivalled technical and customer support. To learn more, talk to one of our application specialists today.

Related Blog Posts:
Water Activity Measurement in Pharma

More Information:

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Related Products

Benchtop Water Activity Meter - Rotronic HygroLab
Temperature-Stabilized Water Activity Analyzer - Rotronic AW-Therm
Rotronic Accessories for Water Activity Measurement
Bluetooth Water Activity Measurement Head - Rotronic AwEasy

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