Navigation: Water activity
    What is water activity
  Test Introduction
Test details
  Salt solutions used
  Calibration samples used
  Desktop instruments
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Results
  Desktop instruments
  Decagon AquaLab 3TE
  Novasina LabMASTER-aw
  Rotronic HygroLab 2
  Portable instruments
  Decagon PawKit
  Rotronic HygroPalm
  Testo 650
Summary
  Desktop instruments
  Portable instruments
 

Water
activity

 
       

EminTech 

 
       
  What is water activity?    
    Water activity quantifies the accessibility of water in a substance.
The property varies between 1 and 0 (zero).
Water activity 1 denotes that water is accessible as in pure water,
water activity 0 denotes that water is not accessible at all.
 
         
  Water activity is an important property  
    Water activity is often a more important property for substance
behaviour than water concentration. Examples include hydrolysis,
solubility, diffusion, protein activity, living tissue properties
and many other applications.
 
           
  Example: Bacterial growth    
    Most microorganisms cannot survive at water activity less than 0,75,
corresponding to high concentrations of common salt (NaCl).
Salt is therefore used for preservation, and water activity,
but not concentration, is the important parameter.
 
         
    Water activity vs. water concentration  
      In many fields, water concentration has been treated as the
important parameter, because concentration generally shows
some type of proportionality to activity.
The real parameter for analysis is, however, quite often water activity.
As this insight is learned, laboratories begin to use water activity
as parameter, increasing the precision of their analytic efforts.
 
         
    The equipment at EminTech includes two instruments:  
    • Decagon AquaLab 3 TE, an advanced dew point instrument.  
    • Testo 610, an instrument for samples with high amounts
  of volatile solvents, unsuitable with the AquaLab instrument.
 
         
  Both instruments are calibrated according to highest standards.  
           
           
  Tests of water activity
measurement instruments
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