Dry matter is Determination method

2024 Author: Isabella Gilson | [email protected]. Last modified: 2023-12-17 03:14

Water is one of the most common chemical compounds on Earth. It plays an exceptional role in the life of the biological world, just as oxygen, being a necessary condition for life, is part of all living beings and participates in their metabolic systems. Determining the water content (percentage of moisture) in the human environment, food, industrial materials, gaseous, solid and liquid substances is one of the many tasks solved in laboratories around the world.

Definition of concept

The most general definition of solids (dry residue in chemistry) is that these are substances from which moisture has been removed. But the moisture contained in a substance or material can be divided into two components:

• one that is contained in the molecules of a substance, or associated;
• that which is contained between the molecules of a substance, or free.

Free water can be removed by physicalmethods: evaporation, drying, distillation, etc. In this case, the structure of the substance can change, but the chemical composition does not. Bound moisture can only be removed under harsher conditions, or even with chemicals alone.

Dry - these are substances in which both types of water are absent. It must be remembered that the surrounding air constantly contains a certain amount of water vapor.

Therefore, dried hot substances must be stored in special containers so that water vapor does not enter them.

Water in food

Food contains large amounts of water. From 70-95% in various fruits and vegetables and up to 4% in milk powder. But the humidity of the product does not indicate the percentage of free and bound water in it, and this plays a leading role in storage. After all, depending on the humidity, the appearance, taste and, accordingly, the time and method of storage change without the appearance of signs of spoilage. Therefore, manufacturers usually indicate not only the period, but also the humidity and temperature of the storage of the product.

In food, water can be bound by proteins and a large number of other organic compounds into stable colloidal systems from which it is difficult to remove.

Water in animal feed

Dry matter may refer to the dry portion of animal feed. A feed nutrient or toxin may be classified as such to indicate its level in animal food. Accounting for nutrient levels in differentfeeds on a dry matter basis (rather than evidence-based) facilitates comparison. After all, all food has different percentages of water. It also allows comparison of the dry level of a given nutrient with the level required in the animal's diet.

Water percentage is often determined by heating the food on a paper plate in the microwave or using the Koster Tester to dry the food. Determination of solids can be useful for low energy feeds with a high percentage of water to ensure adequate energy intake. It has been shown that animals consuming these types of food receive less food energy. A problem called dry matter loss can result from the release of heat caused by microbial respiration. This reduces the content of non-structural carbohydrates, proteins and overall food energy.

How to calculate the amount of moisture

Solid matter content is determined by the difference between the weight of the entire product and its moisture content (moisture content). For this, direct and indirect methods are usually used.

Direct methods help to extract the water contained in the product, and then determine its amount.

Indirect methods such as drying, refractometry, density or conductivity of a solution determine the solids content. Indirect methods can also include the method of exposure to the test substance with chemical reagents.

Difficulties in determining the moisture content of a substance

Quantity determinationwater in a sample is sometimes complicated by the fact that its drying also leads to a change in its chemical composition: volatile substances such as carbon dioxide, some organic acids, ammonia compounds, as well as most alcohols and ethers simply evaporate during the process, and the oxidation of a number of organic substances leads to to an increase in dry weight. It can also increase due to the water contained in the stable hydrophilic colloids.

How to determine the dry residue

Determination of solids is carried out by various methods. Consider the main and most commonly used:

1. Arbitration method. The water content is determined by drying to a constant dry weight when hygroscopic moisture is released. The temperature is maintained strictly defined. The sample is dried to constant weight. There is also an accelerated method, carried out at elevated temperature. In this case, a specific drying time is set, and the process is carried out by sintering into a homogeneous mass with pre-calcined sand. The amount of sand applied should be two to four times that of the sample. Sand is necessary for uniform drying, increases porosity and facilitates the removal of moisture. The process is carried out in porcelain cups for 30 minutes, the temperature is determined by the type of product. Aluminum or glass cups can be used instead of porcelain cups.
2. High frequency drying. Such an apparatus produces infrared radiation and usually consists of two plates, whichinterconnected. The method allows many times to speed up the drying process, and hence the entire study.
3. Refractometry method. The use of this method is usually relevant for substances containing a lot of sucrose: sweets, syrups or juices. In this case, the refractive indices of the sample of the substance and sucrose are compared. Since the refractive index depends on temperature, both solutions are placed in a thermostat before examination. This method accurately determines the amount of solids.

Seldom Used Methods

1. The method of differential scanning colorimetry is to cool the sample below the freezing point of water, while free water will turn into a solid state, and when the sample is heated, the heat spent to melt this water can be found. And bound water will be defined as the difference between total water and frozen water.
2. The method of dielectric measurements is based on the fact that in the presence of partially bound water, its properties as a dielectric differ greatly from the sample where there is no such water. Having determined the dielectric properties of a sample of a substance, the content of free and bound water is found using special tables.
3. The method of measuring heat capacity is to measure the index of frozen water when it is thawed, when hydrogen bonds are broken. At high humidity of the sample, the value of the heat capacity will be determined by free water, the heat capacity of which is 2 times greater than that of ice.
4. The method of nuclear magnetic resonance determines the mobility of water infixed matrix. In the presence of free and bound water, the device determines their presence in the spectrum with two lines at once. One type of water gives only one spectral line. The method is expensive, but very accurate, used for deep studies of the structure of organic substances.
5. The densimetric method begins with determining the specific gravity of the sample. This is the usual way to calculate water in juices, syrups, processed fruits or berries with sugar. The specific gravity is determined with a hydrometer. Knowing it, we use the data given in GOST for the test substance and set the water content in the sample.

It should be noted that the methods for determining solids are not limited to those given in this article.

Recommendations for choosing a research method

For each specific sample of a substance, product or material, its own method for determining dry substances is used. To clarify the method, it is necessary to refer to state standards and regulations that are developed for all food products and their industries.

State Standards

A large selection of methods for determining the dry residue does not mean an independent choice of the desired method. For the correct conduct of the study, it is necessary to familiarize yourself with the state standards and regulations for conducting these analyzes in accordance with GOST.

Thus, GOST 26808-2017 "Canned fish and seafood. Methods for determining dry matter" and GOST 32640-2012, concerning methods for calculating the content of a substance infeed. They describe the processes in great detail, note the features of their implementation, equipment and materials for research.

Other standards and regulations

In addition to state standards, there are a large number of different standards that determine the correctness of laboratory tests for each type of test substance for the dry matter content. These are various OSTs, TU, PCT, MVI and other norms and standards. So, for example, there is RD 118.02.8-88 “Methodology for measuring the content of dry residue (dissolved substances) in wastewater.”