Some commodities where moisture content is important

At Tovatech we frequently get questions from researchers and educators on the use of moisture analyzers.  Some questions are basic, others are more advanced. Here is a sampling and we hope they will be helpful if you are looking into the purchase of a moisture balance.

I was asked to purchase a moisture analyzer but just what does the equipment do?   

A moisture analyzer is used to measure the moisture content of virtually any product where the amount of moisture is important to quality or to meet government and industry standards.

What constitutes moisture?

Moisture can be in the form of a solid, liquid or gas.  If it adheres to the sample surface it can be termed adhesive, free water or hygroscopic moisture.  Moisture absorbed by a material is called absorbed or equilibrium moisture.  Water can also be chemically bonded at the molecular level, in which case it is called water of crystallization or hydrated water. In this case the moisture is called bonding moisture or combined water.

Is “moisture” more than water?

Yes.  Certain volatile substances may also be given off during a moisture analysis.  Procedures should be in place to take these into account. Do not perform analysis on explosive or flammable materials or those that become hazardous on heating.

How is moisture content determined?

There are several methods, but one of the most common is termed loss of weight on heating and drying, also called the thermogravimetric method. Others include the Karl Fischer method, dielectric, infrared absorption, the use of a neutron analyzer, and crystal oscillation. The first two find wide use in quality control labs; infrared and dielectric methods are primarily used in processing.

How is heat applied in laboratory grade thermogravimetric moisture analyzers?

Halogen or infrared heaters are most commonly used.  These are mounted on laboratory analytical balances that can be programmed to conduct the analysis in accordance with procedures recommended by industry trade associations and government agencies.

What is the difference between halogen and infrared heaters?

Halogen lamps are much faster.  They can heat from room temperature to 200⁰C in two minutes.  Both have similar optical characteristics.

How does thermogravimetric analysis compare to the Karl Fischer method?

The Karl Fischer method, while highly accurate, uses hazardous solvents, requires skilled technicians and that the water in the sample be accessible to the reagent in order for the method to work.  The method detects only water, whereas thermogravimetric analyzers detect any volatile substance in the sample. 

How important is sample preparation?

Very important in terms of sample size, weight and placement on the moisture analyzer sample pan.  While your organization or business may have established sample prep procedures among points to consider are included:

• Samples should be representative of the bulk material being tested
• Samples should be tested immediately after being taken from the bulk material, or they could give up or absorb moisture from the local environment
• Small particles will analyze quicker because they increase the surface area.  Grains and beans, for example, should be crushed to get a cross-section of moisture content.  Consider a water-cooled mill to offset the generation of heat during crushing – heat that will impact an accurate moisture analysis.
• Samples should be spread thinly and evenly on the sample pan.  Samples with high moisture or oily content – such as honey, milk, and body lotion – should be placed between fiberglass filters so they spread evenly across the sample pan. This not only increases surface area to speed the analysis but also prevents spattering inside the unit.

How do I determine the correct sample size?

Correct sample size in terms of weight is usually established after several testing procedures.  Moisture analyzer operating manuals may suggest sizes for specific products but these are only suggestions.  In general the sample should be sufficient to cover the surface of the sample tray and distributed to avoid lumps or peaks.  Large sample sizes do not equate to more accurate readings.  Your moisture balance operating manual will specify its maximum weighing range.

What is meant by moisture balance readout?

This is the smallest value that can be read and displayed on the balance.  It is also described as readability.     

What is the lower limit of moisture that can be detected?

Low moisture values such as below 1% are difficult to gauge, and require heavier sample sizes.  For example, for a 1% moisture content you may need a 2 gram or more sample, but for a sample with a 0.1% estimated moisture content you’ll need a 20 gram or more sample.    Lower moisture samples require a more sensitive moisture analyzer – which is determined by its readout.

What is meant by switch off criteria?

This lets researchers program when the moisture analysis is completed and the unit shuts off.  Examples include expiration of set test time, when the decrease in sample weight per unit of time falls below the target value, or manually.

What is meant by moisture balance drying profiles?

Drying profiles are selected when programming the moisture analyzer for particular products and are often spelled out in operating or testing procedures for the products.  Most moisture analyzers offer a choice of drying profiles such as step, fast, ramp, and standard (usually the default setting). 

For additional general information read our post on how to set up a moisture analyzer .

Please contact the scientists at Tovatech for recommendations on selecting and operating a moisture analyzer.