Rotronic reliable measurement of water activity

products-servicesRotronic AG

August 12th 2020

Rotronic, a world-leading Swiss manufacturer of measurement instruments and environmental real time online monitoring systems, offers a wide range of solutions for the reliable measurement of water activity (AW) in substances, including pharmaceutical products and fine chemicals.

Water affects most biological and chemical processes but water activity, also called Equilibrium Relative Humidity (ERH), is of particular concern to industry as directly impacts the physical properties of compounds such as tensile strength, adherence, yield pressure, compaction and elastic recovery.

This means water activity directly affects product characteristics, including microbiological, chemical and enzymatic stability, color, taste, nutritional value, protein and vitamin content, solubility and texture as well as having impact on shelf life in storage and in packaging.

Defining water activity

Water activity is distinct from moisture content, which is defined as total water content in a product.

Water activity, on the other hand, is defined as the free water content and can be measured by quantifying the vapor pressure above a product that is in stable equilibrium with its environment, both in temperature and inherent water vapor pressure.

The distinction is important for the pharma industry because it is this ‘active’ moisture content that directly affects the microbial, chemical and enzymatic stability of perishable products, the cohesion and flow of powders, coating adherence, and caking and compaction properties of particles.

Bound water vs. free water

There are two key forms of water activity within products: bound water and free water.

Bound water is so called because it is chemically bound within the substance, which means it is not available to most organisms, does not act as a solvent on salts or sugars and generates no vapor pressure on heating. In contrast, free water is only physically bound into the substance which means it can be extracted easily, is available for interaction with organisms and will generate vapor when heated.

Measuring water activity measurement solutions

Water activity is a qualitative measure. Therefore full interpretation of results can be complex, since AW is only one of the factors defining product physical properties, shelf life or growth of organisms within product, which are also affected by inherent properties.

Both bound and free water can be measured by infra-red or drying loss. Both processes are quick, taking only a few minutes and providing data that can be used to set critical control points.

AW measurement provides useful fast track for assessing product changes, isolating probable causes and making predictions on shelf life, etc. Moreover, water activity testing is much quicker and less costly than total moisture testing. This is particularly true when dealing with ‘known’ products such as grains, cheese and processed meats whose basic parameters and aw limits have already been defined by regulatory organizations.

Water activity measurement solutions

Rotronic offers a complete range of products for measurement of water activity. The instruments are accurate and boast high efficiency, compatibility and simple calibration.

Modular design means users can combine the measurement heads, insertion probes, bench top display units and handheld instruments as needed to construct optimum solutions to specific applications needs.

Applicable instruments and products include:

AwTherm: Combined temperature-controlled measurement and display unity, including Rotronic’s AW Quick analysis function and supported by HW4-P-Quick software and USB connection.
HygroLab: High-end bench top laboratory analyzer with touch-screen for water activity measurements with up to four measurement probe inputs. Simultaneous or asynchronous measurement with the tried-and-tested AW-Quick measuring function for fast results (typically in under five minutes).
HygroPalm HP23-AW-A: Portable display unit to control with twin probe interconnection and USB ports, featuring AwQuick and HW4 compatibility.
HC2-AW-USB: Bench top measurement head with USB connection, compatible with HW4 software for measuring water activity as well as dew and frost point measurements.
HC2-AW-USB-SW: Bench top measurement head with USB connection, compatible with AWQuick and HW4 software for measuring water activity as well as dew and frost point measurements.
HC2-AW: Bench top measurement head with fitted probe connector, compatible with HW4 software for measuring water activity as well as dew and frost point measurements.
HC2-P05: Portable measurement probe with fitted connector, compatible with HW4 software for measuring water activity as well as dew and frost point measurements. Ideal for dust-free applications such as tablets, gel capsules and granulated plastics.
HC2-HP28: Portable measurement probe with fitted connector, compatible with HW4 software for measuring water activity as well as dew and frost point measurements, featuring 10 mm insertion probe for water activity measurement in dusty bulk materials.
HC2-HP50: Portable measurement probe with fitted connector, compatible with HW4 software for measuring water activity as well as dew and frost point measurements, featuring 10 mm insertion probe for water activity measurement in dusty bulk materials.

Rotronic also offers a series of AW measurement starter sets featuring different combinations of display unit, probe or head, which contain everything needed to measure water activity and calibrate the measuring instruments to confirm sensor performance.