In laboratory analysis in many fields such as chemicals, food, materials and environmental monitoring, the determination of solids content is a fundamental and critical physical indicator. It directly reflects the proportion of non-volatile components in the sample, which is of great significance for product quality control, process optimization and formulation research. Traditional methods rely on step-by-step operations, and there is room for improvement in efficiency and accuracy. The combination of the oven and the analytical balance forms a set of integrated drying and weighing measurement processes, which can significantly improve the consistency, accuracy and work efficiency of the inspection.
Method principle
The core principle of this method is to evaporate the volatile components in the sample, usually water or organic solvents, by heating, and then accurately weigh the remaining solid mass. The key to the combined technology is the use of an analytical balance to perform continuous, precise weighing of samples from the same container (such as weighing flasks or foil dishes) before and after drying, resulting in a direct solids fraction calculation. The basic calculation formula is as follows:
Solids content (ω) = (m₃ - m₁) / (m₂ - m₁) × 100%
Among them:
m₁ represents the quality of the dry constant weight container;
m₂ represents the total mass of the container and the sample before drying;
m₃ represents the total mass of the container and the dried sample.
The formula is expressed in HTML form as follows:
ω =
m₃ - m₁ ⁄ m₂ - m₁ × 100%
Instruments and materials
Successful implementation of this method requires ensuring that instrument performance meets the assay requirements.
| Precision blast drying oven | The temperature range is above 200°C, the temperature control accuracy is ± 1°C, and it has the function of uniform blowing. |
| Analyze the scales | With a sensitivity of 0.1 mg, it has sufficient weighing capacity and stability. |
| Dry container | Glass weighing flasks or aluminum weighing dishes, heat resistant and chemically stable. |
| Dryer | Built-in effective desiccant (e.g. color-changing silicone). |
| Samples | Liquid, slurry, or semi-solid sample to be tested, representative. |
Procedure:
Standardized operating procedures are the basis for obtaining reliable data, and the following are the detailed steps:
Step 1: Container constant weight
Place the clean drying container in an oven and dry it to a constant weight at a preset temperature (e.g. 105°C±2°C). After taking it out, it is cooled in a dryer to room temperature, and its mass is accurately weighed with an analytical balance. Repeat the drying, cooling and weighing process until the difference between the two consecutive weighing results does not exceed twice the analysis balance sensitivity, which is considered constant weight.
Step 2: Sample weighing and drying
Add an appropriate amount of representative sample to a constant-weight container, immediately cap and accurately weigh the total mass m₂. The lid is then opened or removed and placed in the oven to dry at the set temperature. Drying time is determined by pre-experiments based on sample characteristics to ensure complete removal of volatile components.
Step 3: Weigh and calculate after drying
After drying, cover the container and transfer it to a dryer to cool well to room temperature. The same analytical balance was used to accurately weigh the vessel and the total mass of the dried sample m₃. The solid content of the sample can be calculated by substituting the obtained m₁, m₂, m₃ into the above formula.
Notes:
To ensure the accuracy and repeatability of the assay results, the following points should be paid attention to:
| Temperature setting | It should be selected according to the thermal stability of the sample and the properties of volatile components to avoid decomposition or oxidation. |
| Drying time | It must be dried to a constant weight, and insufficient or too long time will introduce errors. |
| cooling process | After drying, it must be cooled in a dryer to prevent moisture absorption of the sample. |
| Balance operation | Weighing needs to be fast and smooth, avoiding temperature, airflow and static interference. |
| Sample volume and morphology | The sample should be evenly spread and of appropriate thickness to facilitate sufficient evaporation of water. |
Scope of application:
The method of combining the oven with the analytical balance closely connects the drying and weighing links, reducing the loss and external environmental interference during the sample transfer process. Its direct weighing method reduces human error and improves the precision of measurement results. This method is suitable for the determination of solids content in various coatings, adhesives, detergents, food slurries, sludge, and various chemical intermediates. For samples containing volatile solvents, there is an option to perform at lower temperatures or vacuum oven conditions to prevent boiling or loss.
Summary
The combination of oven and analytical balance to determine solids content is a classic method with clear principles, strong operability and reliable results. By strictly controlling key links such as drying temperature, time, cooling and weighing, and understanding the influence mechanism of various factors, laboratory personnel can efficiently and accurately obtain solid content data, providing solid data support for product development and quality monitoring in related industries.
References
GB/T 1725-2007 Colored paints, varnishes and plastics - Determination of non-volatile content.
ASTM D2369-20 Standard Test Method for Volatile Content of Coatings。
ISO 3251:2019 Paints, varnishes and plastics — Determination of non-volatile-matter content。