By Rotronic AG
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Rotronic reliable measurement of water activity
Rotronic, the world-leading Swiss manufacturer of environmental measurement and monitoring equipment, 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) is of particular concern to industry as it works directly on the physical properties of compounds such as tensile strength, adherence, yield pressure, compaction and elastic recovery.
This means water activity directly impacts on product characteristics, including flow, caking, spoilage, shelf life, viability, taste and overall quality.
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 organisations.
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 AwQuick analysis function and supported by HW4-P-Quick software and USB connection.
- HygroLab C1: Bench top display unit to control up to four probes using Ethernet or USB connection and with full AwQuick and HW4 compatibility. Also supports frost and dew point measurements.
- 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:Benchtop 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.
Click on Products for more information on Rotronic measurement solutions.
HygroLab C1 display unit can control up to four water activity measurement heads
HygroPalm HP23-AW-A mobile laboratory unitis perfect for on-site water activity measurements to determine the stability and preservability of samples being analysed
HP23-AW-SET-40 water activity measurement starter set