OECD 109 designates a standardized analytical procedure, essential for determining the density of liquids and solids. OECD Guideline No. 109 , dedicated to the determination of the density of liquids and solids.
The OECD 109 test aims to measure density, defined as the ratio of a substance's mass to its volume, expressed in kilograms per cubic meter (kg/m³). This is a fundamental parameter, required in most registration dossiers (REACH, IUCLID, CLP) and essential for characterizing the physical behavior of a substance during formulation, handling, or transport.
The guideline describes several methods, chosen according to the physical state of the substance and its viscosity. It belongs to section 1 of the OECD guidelines, which covers all tests relating to the physicochemical properties of substances (numbers 100 and following). This data is used prior to toxicological and ecotoxicological studies and is essential for assessing the risks associated with the use, storage, or disposal of chemical substances.
The OECD 109 trial benefits from the principle of Mutual Acceptance of Data (MAD), meaning that results obtained in one OECD member or partner country are recognized by all signatories. This limits the duplication of trials, reduces costs for industry, and accelerates the international marketing of chemical substances.
This article presents the principles of OECD 109, the different methods applicable depending on the state and viscosity of the substance, the experimental conditions to be respected, the cases of regulatory application, as well as the technical limits to be anticipated.
Table of Contents
An international framework for physicochemical testing
The density of a substance is essential data at many stages of its regulatory and industrial lifecycle. It is taken into account from the earliest stages of chemical substance registration, particularly under the REACH Regulation, but also for labeling according to the CLP Regulation and the requirements for the transport of dangerous goods. OECD Guideline 109 is part of a set of recommendations published by the Organisation for Economic Co-operation and Development (OECD) aimed at harmonizing testing methods globally.
Created to ensure data comparability between OECD member and partner countries, this guideline allows manufacturers and laboratories to rely on validated procedures to reliably characterize the density of their substances, whether in liquid or solid form. It is included in Section 1 of the OECD guidelines, which focuses on basic physicochemical properties.
A cross-cutting issue affecting many industrial sectors
Density plays a role in a variety of fields: formulation, quality control, regulatory compliance, toxicological modeling, and transportation. It allows for the determination of important parameters such as specific gravity, the weight/volume ratio in formulations, and the stability of certain preparations. In the cosmetics sector, it is used to assess packaging compatibility and texture stability. In the food industry, it allows for the control of solution concentration, product consistency, and their evolution over time.
Density measurement is therefore a cross-cutting analysis, carried out in research, development, and routine industrial processes. OECD 109 is thus an essential tool for professionals responsible for regulatory compliance, product quality, or the development of complex formulations.
A method based on a logic of compliance and security
The value of OECD 109 lies not only in its technical dimension. It is also an essential compliance lever in many contexts: registration of substances according to REACH, preparation of IUCLID dossiers, validation of physico-chemical properties in marketing authorization dossiers, or responses to the requirements of international regulations such as the GHS (Globally Harmonized System) or the United Nations transport rules.
By opting for a standardized and recognized method, manufacturers ensure not only the reliability of their data, but also its acceptability by the relevant authorities. OECD 109 makes it possible to produce robust, reproducible, and harmonized results, while meeting the requirements of quality standards such as ISO 17025 or Good Laboratory Practices (GLP).
What is OECD Test 109?
OECD definition of density
The density of a substance is defined as the ratio of its mass to its volume. This physical quantity characterizes the concentration of matter in a given volume. It is expressed in units of the International System of Units (SI), namely kilograms per cubic meter (kg/m³). The denser a substance is, the greater the amount of matter contained in a given volume.
This property is influenced by several parameters, notably temperature and, to a lesser extent, pressure. Therefore, density is always measured at a specific temperature, usually 20°C or 25°C, to ensure the reproducibility of results.
OECD 109 Test Objective
OECD Guideline 109 aims to provide reliable and harmonized methods for measuring the density of substances, whether in liquid or solid form. It ensures that the reported density is representative, comparable, and scientifically valid.
The test is intended for any pure substance or mixture requiring physicochemical characterization for regulatory purposes. This includes, in particular:
- Chemical substances that must be registered under REACH.
- Formulations to be evaluated for their stability or safety.
- Products requiring classification or labeling according to CLP.
Since density is a determining parameter in the calculation of other properties (density, concentration, buoyancy, apparent viscosity), it also plays a role in toxicological and environmental modeling.
Units and associated standards
The standard unit used in OECD 109 tests is kilograms per cubic meter (kg/m³), but grams per cubic centimeter (g/cm³) are also commonly encountered, particularly in certain industrial sectors. The conversion is direct: 1 g/cm³ is equivalent to 1000 kg/m³.
To guarantee data validity, measurements must be carried out under strictly defined conditions, with calibrated instruments and complete traceability. Laboratories engaged in this type of measurement should ideally hold ISO 17025 accreditation, attesting to the quality of their procedures and compliance with metrological requirements.
OECD 109 does not prescribe a single method, but proposes a set of proven techniques, each adapted to a particular type of sample or physical constraint. The choice of method will depend on the physical state of the substance, its viscosity, its purity, and the specific requirements of the regulatory dossier.
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Why measure density in the laboratory?
A key parameter for the characterization of substances
Density is a fundamental property for any substance, just like melting point, boiling point, or solubility. It allows us to deduce several other characteristics, such as apparent mass density or the proportion of a compound in a mixture. In liquid formulations, it plays a role in calculating concentration, miscibility, and compatibility with containers.
In the field of solids, density allows us to assess the compaction of a powder, the porosity of a material, or the stability of a bulk product. It is also used to predict the sedimentation rate or the mechanical behavior of a material in use.
A requirement of European and international regulations
Density measurement is required in many regulatory frameworks, particularly for chemical, cosmetic, pharmaceutical, and food substances. It is among the data required in REACH registration dossiers (Regulation (EC) No 1907/2006), as well as in IUCLID dossiers submitted to the authorities.
Density is also used in the classification of substances according to the CLP Regulation (Classification, Labelling and Packaging – EC No. 1272/2008), as it influences concentration limits, labelling thresholds, and hazard statements. Finally, it is essential for the rules governing the transport of dangerous goods (UN Regulation, IMDG Code), where it determines the conditions for packaging, labelling, and storage.
Concrete applications in industry
Density plays a role at many stages of an industrial product's lifecycle. During development, it helps design stable formulations, optimize texture and packaging, and predict long-term stability. In production, it serves as a conformity indicator, verifying that each batch meets specifications. In logistics, it influences storage volumes, transport conditions, and associated costs.
In the food industry, it allows, for example, the control of juice concentration, the dry matter content of preparations, or batch-to-batch consistency. In the cosmetics industry, it is used in the analysis of emulsions, phase stability, or product behavior at different temperatures.
Analytical methods described in OECD 109
Methods applicable only to liquids
Some methods described in OECD guideline 109 are exclusively reserved for the analysis of liquid substances. They are based on physical principles adapted to the low mechanical resistance of liquids, but are limited in terms of viscosity.
The hydrometer is one of the simplest methods. It works on the principle of buoyancy: a graduated glass tube is immersed in the liquid, and the density is read directly on the scale according to the immersion depth. However, this method is only suitable for liquids with a dynamic viscosity of 5 pascals-seconds (Pa·s) or less, because above this viscosity, the fluid resistance distorts the reading.
The immersed body method, also based on Archimedes' principle, involves immersing an object of known volume in the liquid and measuring the buoyant force exerted. It allows for the analysis of more viscous liquids, up to 20 Pa·s. This method is better suited to dense substances or those containing thickening agents.
The oscillating densimeter, on the other hand, is based on measuring the vibration frequency of a hollow tube filled with the liquid to be tested. This frequency depends directly on the liquid's density. It is a very precise and rapid method, suitable for small volumes, but it is also limited to viscosities below 5 Pa·s.
Methods applicable only to solids
For solid substances, OECD 109 recommends two distinct methods: the air comparison pycnometer and the compaction test.
The air comparison pycnometer measures the volume of a solid sample using a cylinder of variable volume in a controlled environment (air or inert gas). The volume displaced by the sample is compared to a reference volume, and then the mass is measured independently. This method is suitable for fine powders and granular solids.
The compaction test determines the apparent density of powders or granules after agitation or vibration. It is used, in particular, to evaluate the compressibility, flowability, or mechanical stability of a bulk solid.
Methods applicable to liquids and solids
Some methods are versatile and can be used for substances in liquid or solid state, depending on the nature of the sample and the experimental conditions.
The hydrostatic balance relies on weighing a sample in air and then immersing it in a reference liquid. The difference in mass allows the density to be calculated according to Archimedes' principle. This method is suitable for compact solids and low-viscosity liquids (≤ 5 Pa·s).
The pycnometer is a widely used method, particularly for viscous liquids (up to 500 Pa·s) or finely divided solids. It consists of a flask of known volume, filled with the sample, and then weighed with milligram-level precision. This method is simple, reliable, and suitable for many types of substances, provided that cleaning and filling are carried out meticulously.
How is an OECD 109 test conducted in the laboratory?
Method selection based on the sample
Before proceeding with the analysis, the laboratory must evaluate the characteristics of the substance to be tested. The physical state (liquid or solid), viscosity, purity, particle size , and thermal stability can all influence the choice of method to be applied.
The choice of method also depends on the constraints of the regulatory dossier: requirements for a GLP protocol, comparability with previous results, available volume, or required level of precision. This selection step is crucial to ensure the relevance of the results obtained.
Sample preparation and experimental conditions
Samples must be prepared under strict conditions to prevent contamination, evaporation, or temperature fluctuations. They are packaged in clean, inert, airtight containers compatible with the chemical nature of the substance. For liquids, the temperature is generally maintained between 20°C and 25°C, depending on the chosen method.
The laboratories then calibrate the instruments (balance, densimeter, pycnometer) using certified reference substances. This step guarantees the traceability and metrological conformity of the measurements. Blank tests and duplicates are often carried out to ensure the stability of the experimental conditions.
Performing the measurement and calculating the density
Density measurement is performed by strictly following an internally validated protocol, sometimes derived directly from OECD guidelines. The calculation is based on mass and volume data measured with milligram-level precision. Corrections may be applied depending on temperature, particularly for substances sensitive to temperature variations.
Each test is performed multiple times to assess the repeatability and variability of the results. The laboratory then calculates a weighted average and measurement uncertainty, in accordance with the requirements of ISO 17025. The results are presented in a comprehensive analytical report, along with all raw data and experimental conditions.
Applicable quality standards
The OECD 109 test can be performed under two distinct quality frameworks: under GLP (Good Laboratory Practice) conditions, or outside of GLP. The GLP framework is required for REACH registration or a formal regulatory application. It imposes strict procedures for quality assurance, document traceability, archiving, and sample management.
Outside of Good Laboratory Practices (GLP), analyses are generally conducted under ISO 17025 accreditation, the reference standard for testing laboratories. This standard guarantees the technical competence of the staff, the reliability of the equipment, and the robustness of the methods used. In all cases, the results must be usable in regulatory documentation and therefore comply with the requirements of the OECD and the relevant authorities.
Rigorous execution of OECD 109 assays is essential to ensure the scientific reliability and regulatory recognition of the data. Each step of the process is structured, documented, and validated to meet the highest standards of analytical quality.
In what cases is the OECD 109 test required?
Registration of substances under REACH
One of the most frequent uses of the OECD 109 test concerns the registration of chemical substances under the REACH Regulation (Regulation (EC) No 1907/2006). Any company manufacturing or importing a chemical substance in quantities exceeding one tonne per year must provide a complete technical dossier, including the physicochemical characterization of the substance.
Density is among the basic data required in section 4 of the IUCLID (International Uniform Chemical Information Database) format. It helps to complete the physicochemical profile of the substance and can influence other regulatory parameters such as concentration calculations, exposure limits or risk assessments.
Classification and labelling according to the CLP regulation
Under the CLP Regulation (Classification, Labelling and Packaging – EC No. 1272/2008), density is used to determine the classification of a substance or mixture. It plays a role in calculating mass concentrations, particularly when assessing whether a substance meets or exceeds certain hazard thresholds.
Density is also useful for determining the mass of a product contained in a given package, which influences the mandatory information on the label. In the case of complex mixtures, it ensures a homogeneous distribution of components and guarantees the product's compliance with applicable safety standards.
Transport and storage of dangerous goods
International regulations relating to the transport of dangerous goods, such as the United Nations regulation, the IMDG code for maritime transport, or the ADR regulation for road transport, require that certain physico-chemical data be provided in the safety data sheet (SDS).
Density is one of the mandatory data points, as it determines the type of container, safety measures, securing protocols, and classification within packaging groups. An error in determining density can lead to regulatory non-compliance, a risk of leakage, or poor load distribution.
Marketing of industrial products and quality validation
Beyond regulatory requirements, OECD 109 testing is frequently requested by quality, R&D, or product safety departments in the chemical, cosmetic, food, and pharmaceutical industries. It allows for the documentation of technical data sheets, the validation of formulations, and the verification of a production batch's conformity to expected specifications.
For example, in the cosmetics industry, density can be a criterion for the stability of an emulsion or gel. In the food industry, it is used to control the concentration of dry extract or the consistency of a liquid product. In the materials industry, it is used to identify a polymer, control porosity, or evaluate apparent density after compression.
Limitations and technical considerations
Influence of environmental parameters
Density is a property directly influenced by temperature, and to a lesser extent by atmospheric pressure. An increase in temperature tends to decrease the density of liquids and solids, while increasing their volume. Therefore, measurements must be carried out at a controlled temperature, generally 20°C or 25°C according to applicable standards.
Even slight temperature variations can introduce errors of several units in the final measurement. Laboratories therefore use thermostatic baths, climatic chambers, or integrated sensors to stabilize the measurement environment and ensure the reproducibility of results.
Adapting the method to the viscosity or nature of the sample
Each method described in OECD 109 has a viscosity range for which it is suitable. For example, the hydrometer and the oscillating hydrometer are only valid for liquids with a viscosity of less than 5 pascals-seconds. Above this range, the internal resistance of the fluid prevents a reliable reading.
Similarly, very fine powders, hygroscopic samples, or volatile substances require special precautions. It may be necessary to work under an inert atmosphere, to package samples under vacuum, or to use specific materials to prevent contamination or mass loss.
A poorly prepared sample or a poorly chosen method can lead to erroneous results, not representative of the reality of the product.
Accuracy of measuring instruments
Instruments used in OECD 109 testing must meet strict requirements for accuracy and stability. For example, an analytical balance used for a pycnometer must have a sensitivity on the order of milligrams or tenths of milligrams. Any calibration deviation, vibration, or air current can distort the measurement.
The pycnometers themselves must be carefully cleaned, dried, and handled with gloves to avoid any alteration of the measured weight. Similarly, oscillating densimeters must be regularly checked using calibration fluids to ensure their proper functioning.
Repeatability and validation of results
As with any physicochemical analysis, density measurements must be repeated several times to ensure data reliability. Significant discrepancies between the obtained values may indicate sample instability, poor homogenization, or a technical failure. It is therefore recommended to perform at least three successive measurements and analyze their variance.
Measurement uncertainty must be calculated and included in the final report, in accordance with the requirements of ISO 17025. In the case of analysis under GLP conditions, all operations must be documented, verified by quality assurance, and archived according to current good practices.
These technical considerations should not be neglected, as they directly condition the validity of the data produced in the context of an OECD 109 test. A rigorous approach, adapted to the nature of the sample and based on reliable instruments is essential to guarantee a precise, repeatable density measurement that meets the expectations of the authorities.
How YesWeLab supports you in OECD analysis 109
A network of accredited, multi-sector laboratories
YesWeLab collaborates with over 200 partner laboratories in France and Europe, selected for their technical expertise, specialized equipment (pycnometer, hydrostatic balance, oscillating densimeter, hydrometer, etc.) and recognized accreditations such as ISO 17025, GLP, or GLP. This rigorous selection process ensures the reliability of results, regardless of the type of substance analyzed (liquid, solid, viscous, powder) or the sector involved (chemicals, cosmetics, food processing, materials, environment, animal health, nutraceuticals, etc.).
YesWeLab offers OECD 109 testing under GLP or non-GLP conditions, depending on the project's regulatory framework. GLP studies ensure complete traceability, equipment validation, enhanced quality control, document archiving for at least ten years, and the legally required storage of samples. These requirements guarantee the acceptability of results in REACH and IUCLID dossiers, as well as with the relevant authorities in France and internationally.
A digital platform to centralize and simplify your analyses
YesWeLab provides its clients with an intuitive and secure digital platform that centralizes all analysis requests. This interface allows users to search for services, send samples, track the status of tests in real time, view documents, and retrieve final results from a single location.
This digital solution reduces delays, minimizes the risk of transmission errors, improves traceability, and facilitates overall management of analyses. It also allows users to view the history of services performed, generate activity reports, and anticipate future needs.
Choosing YesWeLab for your OECD 109 test guarantees the quality, compliance and reliability of your analyses, while benefiting from simplified management and expert support.
