Hydroxyl Number Assay

The hydroxyl number corresponds to the quantity of hydroxyl groups (–OH) present in a substance. This measurement is essential for evaluating the chemical functionality and reactivity of samples containing hydroxylated compounds such as oils, resins, polymers, or fatty esters .
In industrial formulations, it allows for the characterization of raw materials , the monitoring of polymerization or esterification reactions , and the finished product quality

Principle and operation of the method

The determination of the hydroxyl value is based on a titrimetric analysis .
The sample is first acetylated using acetic anhydride, which reacts with the hydroxyl groups to form esters. The excess unreacted anhydride is then hydrolyzed and titrated using a standard alcoholic potassium hydroxide (KOH) .

The hydroxyl value is expressed in milligrams of KOH required to neutralize the hydroxyl groups present in one gram of sample . This value is directly proportional to the degree of functionalization of the material or fat analyzed.

The method offers good reproducibility and high precision , particularly suited to samples from the chemical, cosmetic, food or polymer industries.

Analytical performance and related analyses

The hydroxyl index is often coupled with other physicochemical parameters for a complete characterization of matrices:

• the measurement of the acid value ,
• the measurement of the peroxide value ,
• the iodine index measurement,
• or the measurement of free fatty acids .

These additional analyses make it possible to determine the degree of oxidation , chemical purity , stability and molecular functionality of a wide range of products (vegetable oils, polymers, resins, additives, lubricants or composite materials).

Applications and areas of use

The hydroxyl index measurement applies to several sectors:

• Human nutrition and nutraceuticals : evaluation of the chemical quality and stability of natural oils and fats.
• Animal nutrition : control of lipids in raw materials and feed formulations.
• Plants and natural extracts : characterization of the functionality of essential oils or enriched extracts.
• Materials and polymers : control of the reactivity of polyols, polyesters, polyurethanes or epoxy resins.

It is a key indicator of the chemical reactivity and functional performance of raw materials and finished products.

The advantages of the YesWeLab service

YesWeLab relies on a network of ISO 17025 and COFRAC accredited laboratories specializing in the physicochemical analysis and characterization of materials and fats. Each request is directed to the most suitable laboratory based on the matrix, method, and applicable standards.

Thanks to its intuitive digital platform , YesWeLab simplifies the management of your analyses: request a quote, submit samples, track them online, and receive results quickly.
Since 2020, numerous manufacturers in the food, cosmetics, chemical, and materials have trusted YesWeLab for their analytical and regulatory needs.

For any specific needs in hydroxyl number assay , contact our scientific team to obtain a personalized quote and technical support tailored to your matrices and objectives.