Introduction
In many industrial fields such as chemicals, coatings, inks, adhesives, and food, non-volatile content (or solid content) is a key parameter for evaluating product performance and quality control. The accuracy of the measurement results directly affects the adjustment of the production process and the quality of the final product. At present, the gravimetric method and volumetric method are mainly used for determination in the laboratory. This paper aims to systematically compare these two classical methods from the aspects of principle, operation process, applicable scenarios and accuracy influencing factors, and provide a reference for technicians in related fields to choose methods.
Overview of the principles of the method
Gravimetric method, the core principle of which is to completely evaporate the volatile components in the sample by heating, and then accurately weigh the mass of the residue. Non-volatile content (NvThe formula is:
Nv = (m2 - m0) / (m1 - m0) × 100%
Where, m0for container mass, m1is the total mass of the container and sample, m2It is the total mass of the container and residue after heating.
The volume rule is usually based on a specific chemical reaction, such as titration, to determine the concentration of a component in a sample that is associated with non-volatile components, and then convert the content to the content. Its precision relies heavily on the specificity of chemical reactions and the accuracy of titration operations.
Analysis of factors affecting accuracy
The accuracy of both methods is constrained by a range of different factors. Understanding these factors is crucial for obtaining reliable data.
| The main influencing factors of the gravimetric method | The main influencing factors of the volume method |
| Weighing instrument sensitivity and calibration status | calibration and reading error of burette and pipette |
| Stability of heating temperature and time control | Accuracy of standard titration solution concentrations |
| Sample uniformity and representativeness | The degree of selectivity and completeness of chemical reactions |
| Effects of ambient humidity on samples and containers | Subjectivity of indicator endpoint judgment |
| Whether the volatile components are completely expelled | Interference from sample preparation |
Comparison of operation process and applicability
The gravimetric operation steps are relatively straightforward and usually include sampling, weighing, heating, cooling, and reweighing. This method is suitable for the vast majority of samples that are stable under heating conditions and volatile components are easily removed, such as most resins, coatings, etc. Its advantage is that the principle is intuitive and does not require complex reagents.
The volume law requires the development or selection of specific chemical analysis methods based on sample characteristics, involving standard solution preparation, titration, and other steps. It is more suitable for quantification of specific chemical components in non-volatile components, or when the sample may decompose when heated and gravimetric method is not available. However, method development cycles can be longer.
Data comparison and discussion
Under ideal conditions, both methods can achieve a high level of precision for homogeneous samples with well-defined compositions. The repeatability standard deviation of gravimetric methods is usually controlled to within 0.3%, while the precision of volumetric methods is highly dependent on specific chemical reactions, and their coefficients of variation can vary from method to method.
It should be pointed out that the gravimetric method measures the mass of total non-volatile substances, including all non-volatile components such as resins, fillers, and inorganic salts. The volumetric method measures the content of specific components, and the results of the two may differ in a physical sense, so it is necessary to be cautious when directly comparing the values. The choice of method should first depend on the purpose of the test and the nature of the sample.
Conclusion
Gravimetric method and volume method are effective means to determine non-volatile content. Gravimetric methods are widely used in routine quality control due to their versatility and ease of operation. The volume law is valuable when quantitative analysis is required for specific components. In practical work, it is recommended to give priority to the methods specified in the country, industry or international standards (such as GB/T, ISO, ASTM, etc.) corresponding to the product. When introducing new methods, laboratories should conduct sufficient method validation to evaluate their precision, accuracy, and applicability to ensure that the test results meet the requirements of quality control.
References
GB/T 1725-2007 Colored paints, varnishes and plastics - Determination of non-volatile content
ISO 3251:2019 Paints, varnishes and plastics — Determination of non-volatile-matter content
ASTM D2369-20 Standard Test Method for Volatile Content of Coatings
Analytical Chemistry, Related Titration Principles Chapter.