Basics of Dynamic Vapor Sorption Analysis
Dynamic water vapor sorption analysis is a precise and reliable method for investigating the temperature-dependent interaction between a material and the ambient humidity.
The basic principle of the ProUmid sorption test systems is to measure the weight change of a sample as a function of the prevailing ambient conditions. In this way, information about the kinetics of water vapor sorption and desorption as well as about the equilibrium state depending on a given relative ambient humidity are obtained.
The application notes below summarize some basics of DVS measurements and explain theories for data interpretation. The application notes are intended to assist in obtaining reliable and reproducible results.
Application notes
Humidity sensor calibration using saturated salt solution
Reliable and reproducible results are crucial for measurements in the fields of quality assurance and R&D. To ensure the accuracy of the SPS and Vsorp devices, in addition to routine maintenance, the humidity sensor should be verified and calibrated in regular intervals. Application note 18-01 introduces a method for calibrating the humidity sensor using saturated salt solutions and explains the principle of the method.
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Certification of Microcrystalline Cellulose as a humidity reference for gravimetric DVS instruments
Microcrystalline Cellulose has been certified by ProUmid as reference material for gravimetric DVS devices. The Application note AN-1802 describes the stability study and the validation of the material by a round robin test that were carried out for certification.
Microcrystalline Cellulose as a humidity reference for gravimetric DVS instruments
The SPS and Vsorp instruments require regular moisture sensor validation to ensure accurate and reliable measurements. For this purpose, the MCC reference material is available. The Application note AN-1803 describes a convenient and time-saving method using an inline validation routine.
Speed vs. accuracy in moisture sorption analysis
Dynamic water vapor sorption measurements are often time-consuming, since for reproducible results the equilibrium state between the water content of the sample and the relative ambient humidity should be awaited.
Depending on the sample characteristics, this can take several days per moisture level and acceleration is only possible within a very limited range.
To illustrate the importance of sufficiently long measurement times, the parameters for equilibrium detection were varied in Application Note 17-01, thus demonstrating the influence of accelerated measurement settings on the results.
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Moisture Sorption Isotherms
Moisture sorption isotherms are defined as the “Relationship between the equilibrium moisture content of a substance and the relative humidity of the ambient air at a given temperature”. The resulting information about the water content as a function of the water activity is essential to characterize a material with regard to microbial, (bio)-chemical and physical stability. In addition, conclusions can be drawn about the type of water binding or moisture-induced processes based on the characteristic shape of a sorption isotherm. The White Paper 21-01 explains how a sorption isotherm can be obtained, presents theories for interpreting and illustrates this using some practical examples.
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