Questions and answers on moisture balances
We often receive questions from researchers and quality control managers on the use of scales and moisture analyzers. Some questions are basic, others are more advanced. Here is a sampling of the most frequent, hoping they will be useful if you are considering purchasing a scale for humidity.
We clarify the terminology immediately, in this article the terms: humidity balance, humidity analyzer, thermal balance and thermal balance are considered synonyms. A moisture analyzer is used to measure the moisture content of any product where the amount of moisture is important for quality or to meet legislative and / or industrial standards. Moisture can come in the form of a solid, liquid or gas. If it adheres to the sample surface, it can be called adhesive, free water or hygroscopic moisture. Moisture absorbed by a material is called absorbed moisture. Water can also be chemically bound on a molecular level, in which case it is called crystallization water or hydrated water. In this case humidity is called bond moisture or combined water.
Is humidity more than water?
Yes. Some volatile substances can also be emitted during a moisture analysis. Procedures should be in place to take this into account. Do not perform analysis on explosive or flammable materials or on those that become dangerous for heating.
How is the moisture content determined?
There are several methods, but one of the most common is called weight loss by heating and drying, also called the thermo gravimetric method. Others include the Karl Fischer method, the dielectric, and the infrared absorption, the use of a neutron analyzer and the oscillation of the crystal. The first two are widely used in quality control laboratories; infrared and dielectric methods are mainly used in processes. It can be determined by one of the best Weighing moisture analyzers calibration. The halogen heaters or infrared lamps are commonly used and mounted on laboratory analytical scales, which then become thermo balances which can be programmed to conduct the analysis according to the procedures recommended by the industry associations and by governmental agencies.
What is the difference between halogen and infrared heat balances?
Halogen lamp moisture scales are much faster. They can heat from room temperature to 200 ° C in two minutes. Halogen technology allows for rapid heating to minimize test time. The heating technology with halogen lamps starts drying each sample within a few seconds and is 40% faster than traditional infrared methods.
How does thermo gravimetric analysis compare with the Karl Fischer method?
The Karl Fischer method, although extremely accurate, uses hazardous solvents, requires expert technicians and the water in the sample is accessible to the reagent for the method to work. The method detects only water, while thermo gravimetric analyzers detect any volatile substance in the sample.
How important is sample preparation?
The size of the sample, the weight and the positioning on the pan of the moisture analyzer are very important. It is good to first follow the pattern below: The samples must be representative of the mass material to be tested and must be tested immediately after being taken from the bulk material or they could release or absorb moisture from the local environment. If divided into small particles, the thermal balances will analyze faster because they increase the surface. Cereals and beans, for example, must be crushed to obtain a cross section of the moisture content. The samples must be distributed thinly and evenly on the weighing pan. Samples with high humidity or oily content – such as honey, milk and body lotions – must be placed between the glass fibers filters so that they spread evenly on the sample pan. This not only increases the surface area to speed up the analysis but also prevents spraying inside the unit.
How can I determine the right sample size?
The correct sample size in terms of weight is generally established after several test procedures. The operating manuals of the thermal scales may suggest sizes for specific products, but these are only suggestions. In general, the sample should be sufficient to cover the surface of the tray of the aluminum plate and distributed to avoid lumps or spikes. Large samples do not equate to more accurate readings. The humidity balance operating manual will specify its maximum weight range.
What is the minimum humidity limit that can be detected?
Low humidity values of less than 1% are difficult to measure and require heavier sample sizes. For example, a sample of 2 or more grams may be required for a moisture content of 1%, but a sample of 20 grams or more is required for a sample with an estimated moisture content of 0.1%. Lower humidity samples require a more sensitive moisture analyzer.
Peter Sundin was born and raised in New Jersey. He has contributed to Buzz Feed, Details and TODAY and served as a commentator for NPR, MSNBC and HuffPost Live. As a journalist for Morning News Ledger, Peter mostly covers national news. Aside from earning a living as a freelance journalist, Peter also works as a dog walker.