Oil absorption value is generally referred to the ability of inorganic powder to adsorb oil [1]. In the preparation process of inorganic-organic composite materials, the oil absorption value of inorganic powder has significant impact on the mechanical strength and functionality of the composite materials [2], [3], [4]. For example, for the barium sulfate/epoxy resin radiation shielding materials [5], barium sulfate powder with appropriate oil absorption value can significantly improve dispersion in epoxy resin and the interaction between inorganic and organic interfaces [6], resulting in high strength expected radiation resistance of the shielding material [7]. Therefore, a rapid and accurate method for determining the oil absorption value of inorganic powder is of great significance in guiding the production process control and product quality assurance of inorganic powder.

At present, the main method for determining the oil absorption value of inorganic powder is manual method [8]. The manual method consists of placing a given mass of inorganic powder on a glass plate and slowly dropping oil drops onto the surface of the powder using a dropper filled with oil. The grinding is continuously turned over with a palette knife to ensure uniform wetting of the oil and inorganic powder particles. When the inorganic powder became a non-fragile cluster and there was no oil stains on the glass plate, the detection reached the endpoint. Finally, the oil absorption value of the powder is determined by recording the amount of oil absorbed by the inorganic powder. Obviously, the entire testing process needs to be very slow. The speed and time of grinding and mixing during the operation of the method, as well as the state of affairs when determining the endpoint, have impact on the experimental results. The method has poor repeatability and large measurement errors [9]. Therefore, it is very important to develop a low-cost, efficient and accurate method to measure the oil absorption value of inorganic powder.

Headspace gas chromatography is an effective technique for quantitative analysis of volatile substances in a wide range of complex matrix samples [10], [11], [12]. With the advantages of high detection efficiency and accurate results, it has been widely used in many fields. In our previous work, we have developed some new methods that use headspace gas chromatography to determine starch gelatinization temperature [13], water vapor transmission rate of paper [14], and softening point of rosin [15], and water absorption capacity in wheat flour [16]. The core idea of these methods is to analyze the interaction (adsorption or migration) between the tracer and the analyte, and/or derive some new mathematical models to describe the relationship between them. As the oil absorption ability of inorganic powder could affect the equilibrium and distribution of volatile substances in gas and solid phases. As mentioned in previous, the difference in pressure on the oil-powder mixture and the fuzzy judgment of the detection endpoint have significant negative impact on the repeatability and accuracy of the conventional manual method. By contrast, tracer-assisted headspace technology technique can not only be used to study complex mass transfer processes such as adsorption and desorption, but also efficiently determine the endpoint of some complex reactions. Thus, we believe that the tracer-assisted HS-GC method can be applied for determining the oil absorption value of inorganic powder.

A new method for determining the oil absorption value of inorganic powder based on tracer-assisted headspace chromatography was developed in this paper. The study focused on introducing a methodology and establishing a correlation between the tracer signal measured by HE-GC and the oil absorption values of the inorganic powder measured by the manual method on a set of inorganic powder samples. The optimization of the measurement conditions (equilibrium time, equilibrium temperature and solution volume) and the reproducibility and accuracy of the method were also evaluated.