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Guide to Moisture Analysis


Fundamentals and Applications in Laboratory Weighing

Guide to Moisture Analysis
Guide to Moisture Analysis

This guide to moisture analysis assists you in reliably determining moisture content with a halogen moisture analyzer, and covers the following topics:

  • Introduction to moisture analysis
  • Measuring principle
  • Installation
  • Routine testing (calibration)
  • Sample handling, and preparation
  • Method development to match results from the drying oven
  • Special samples (e.g. liquids, volatiles, plastics)
  • Method validation
  • Comparison of moisture determination technologies
  • Glossary of technical terms

Download the free Guide to Moisture Analysis, and learn the fundamentals of moisture analysis, and its applications. Get helpful information about correct installation, flawless operation, quick measurement, and achieving reliable, and precise analysis results.



Introduction to Moisture Analysis

Moisture determinations need to be carried out reliably, and at speed so that any interventions in the production process can be made quickly to avoid interruptions. One quick, and accurate way of determining moisture is thermogravimetric measurement using a halogen moisture analyzer: The sample is weighed, and heated with an infrared radiator (halogen lamp). The loss in weight is continuously recorded, and drying ends once a defined criterion is reached. The moisture content is automatically calculated from the difference in weight.

Measuring Principle

The halogen moisture analyzer works along the lines of the thermogravimetric principle, i.e. the sample's start weight is recorded, then a halogen radiator dries it while an integrated balance continually records the sample weight. The total loss in weight is interpreted as the moisture content. Drying with the halogen radiator is a further development of the infrared drying method. The heating element consists of a glass pipe filled with halogen gas. As the mass of the halogen radiator is very low compared with that of a conventional infrared radiator, the maximum heating output can be reached quickly, and outstanding controllability is achieved. Combined with even distribution of the thermal radiation over the entire sample surface, this is indispensable to achieve repeatable results.

In contrast to the traditional oven in which the sample is heated using convection, and dried over a long period of time, the sample in the halogen moisture analyzer absorbs the infrared radiation (thermal radiation) from the halogen lamp, and as a result, heats up very quickly.



Since moisture measurement using the moisture analyzer is based on a high-precision weighing procedure, accuracy, and repeatability are closely linked to the instrument's location. To ensure that your moisture analyzer works under the best conditions, please observe the guidelines mentioned in above document.

Routine Operation

To ensure precise measurement results the following information about care, calibration intervals, and maintenance should be observed:

  • By regularly calibrating (testing), and if necessary adjusting the heating module, you will ensure consistent, and reproducible heat output for the entire lifetime of your instrument. We therefore recommend that you define test intervals for testing the weighing unit, and heating module (depending on risk).
  • To ensure quality moisture results at all times, METTLER TOLEDO offers SmartCal™. This unique temperature sensitive substance with a known moisture content is used in one single test to quickly, and easily verify the instrument’s overall functionality. The SmartCal test is based on a regular measurement with a moisture analyzer. Refer to the SmartCal User Guide for more information: SmartCal Moisture Analyzer Test Substance User Guide
  • Annual maintenance performed by the METTLER TOLEDO service team will guarantee the quality, measurement accuracy, and value retention of your halogen moisture analyzer.

Sample Handling and Preparation

The correct preparation of samples once they have been taken is also key to repeatable and reliable results.

  • Ensure even granulation (particle size).
  • If necessary increase the sample surface area by breaking up the sample.
  • This will ensure a better and faster release of moisture during drying (faster diffusion of moisture to the surface).
  • The sample should not be heated at this stage as this would cause moisture to be lost during preparations.
  • Mechanical crushing can be carried out e.g. using a mortar, grinder (watercooled) or simply by cutting.

Method Development to Match the Drying Oven

There are often statutory requirements, standards customarily used in the trade or internal corporate instructions for substances which define the method of moisture content determination. The oven method (loss on drying) or Karl Fischer titration is usually used as the reference procedure. In such cases, the aim is to obtain the same results with the halogen moisture analyzer as with the reference procedure (or for the deviation from the reference value to be known, and reproducible). In order to achieve this, adjustments must be made to the setting parameters such as drying temperature, drying program, and sample weight as well as the handling of the sample. This is known as method development where the aforementioned parameters describe a method.

Special Samples

Certain samples need a special procedure for quickly, and correctly determining moisture. This section contains information about how you can work with such samples to optimize moisture determination.

Liquid, and very moist samples:

  • Use the glass-fiber filter.
  • Tare the filter with the sample pan, and then place the sample on it.
  • Rapid drying is suited to samples with a very high moisture content (> 30%).
  • In this process, the target temperature is exceeded by 40% for 3 minutes to accelerate the measuring process.
  • Step drying can be used as an alternative to rapid drying. Here the duration of the temperature increase, and the temperature are freely selectable.

Overview of Different Technologies for Moisture Determination

Various measurement processes have been developed for determining moisture content. The table below shows a selection of typical measurement technologies, and describes the advantages, and disadvantages of these procedures.

Drying Oven

Drying Oven


Measuring method

Heating of sample by convection. The sample is dried in the oven for a defined period of time at constant temperature. Mass is determined before, and after drying. The moisture content percentage is determined from the difference in weight before, and after drying.


● Often reference procedure (for historical reasons this procedure often forms part of legislation)
● Several samples can be determined at the same time
● Large sample volumes possible


● Very long determination period (hours)
● Substances other than water may evaporate
● Prone to errors because of the high level of manual handling, and calculations involved
● Unsuitable for at-line use - requires analytical balance, and dessicator

Halogen Moisture Analyzer


Measuring method

Heating of sample through absorption of IR radiation from a halogen radiator. Continual determination of mass during drying process. The moisture content percentage is determined from the difference in weight before, and after drying.


● Quick measurement (typically 5-15 min.)
● Simple handling, no manual calculations
● Compact instrument. No balance or desiccator required
● Suitable for at-Iine use


● Substances other than water may evaporate

Karl Fisher Titration

Chemical Oxdiation Reaction

Measuring method

The chemical reaction of water with a Karl Fischer reagent (containing Iodine, and sulphur dioxide) is monitored with a polarized sensor to determine the water content. This is either performed volumetrically, with the addition of the reagent measured, or coulometrically, where the reaction is driven in-situ, and is proportional to electrical current applied.


● Water specific, no other solvent or "moisture" determined
● Fast, typically 0.5 to 3 mins per sample
● Measure from 2ppm to 100% water
● Compact instruments, automatic calculations, connect METTLER TOLEDO balances for complete result calculations


● Requires dedicated chemicals, and chemical know-how
● Sample preparation can be critical for complete water extraction (homogenizer, long extraction times)

Technical Terms

Moisture (moisture content): In thermogravimetric processes the moisture of a material includes all substances which volatilize during warming, and therefore contribute to the material's loss of mass. Alongside water this may also include alcohol or decomposition products. When using thermogravimetric measurement methods (drying using infrared, halogen, microwaves or ovens) no distinction is made between water, and highly volatile components.

Drying oven procedure: Thermogravimetric method for determining the moisture content of a sample. This sample is dried in the oven for a defined period of time at constant temperature. The moisture content percentage is determined from the difference in weight before, and after drying. For historical reasons this procedure often forms part of legislation (food regulations, USP etc.).