Volatile Matter and Loss on Drying Testing: Principles, Methods, Standards, and Applications

Volatile matter and loss on drying (LOD) testing are fundamental gravimetric analyses used to quantify moisture and volatile constituents in coal, coke, plastics, rubber, pharmaceuticals, food products, and industrial chemicals. Accredited third-party laboratories perform these tests in accordance with ISO, ASTM, EN, JIS, and GB standards to support quality control, product specification, trade settlement, and regulatory compliance. This article explains the technical principles, sample types, testing items, analytical methods, and typical applications of volatile matter and loss-on-drying determination.

Technical Overview

Volatile matter (VM) and loss on drying (LOD) are two of the most widely performed gravimetric tests in materials characterization. Both methods are based on a simple but powerful principle: a sample is weighed before and after a controlled thermal treatment, and the difference in mass is attributed to the release of water and other volatile constituents.

Loss on drying measures the mass lost when a sample is dried under specified temperature, time, and atmosphere conditions—typically 105 °C to 110 °C in a convection oven until constant mass is reached. The value includes free water, bound moisture, and any low-boiling volatile substances evaporated below the drying temperature. In contrast, volatile matter determination subjects the sample to a much higher temperature (for example, 900 °C ± 10 °C for coal and coke) in an oxygen-free or air-limited environment, capturing all thermally decomposable constituents other than moisture.

These parameters are critical indicators of material quality, processing behavior, and commercial value. In coal, volatile matter content is a primary parameter for rank classification, combustion performance, coke yield, and price settlement. In polymers, residual moisture and volatiles affect melt processing, causing defects such as bubbles and degradation. In pharmaceuticals and food products, moisture content directly influences chemical stability, microbial risk, texture, and shelf life.

Testing Samples

Coal, Coke, and Solid Mineral Fuels

Hard coal, lignite, coke, and coal blends are routinely tested for total moisture, moisture in the analysis sample, and volatile matter as part of proximate analysis. Testing is typically performed according to ISO 562, ISO 589, ASTM D3173, ASTM D3175, GB/T 211, GB/T 212, and JIS M 8812.

Plastics and Polymer Materials

Thermoplastic resins, engineering plastics, masterbatches, polymer granules, and compounds are tested for residual water content and volatile fractions that influence injection molding, extrusion, and film production. Relevant methods include ISO 15512 and ASTM D6980.

Rubber and Elastomers

Raw natural rubber, synthetic rubber, and rubber compounds are analyzed for volatile-matter content to assess drying efficiency and formulation consistency, commonly following ISO 248.

Pharmaceutical Raw Materials and Finished Products

Active pharmaceutical ingredients, excipients, granules, and finished dosage forms are tested for loss on drying as an identity, purity, and stability attribute, using validated pharmacopoeial-style gravimetric procedures.

Food, Feed, and Agricultural Products

Grains, flours, milk powders, spices, feed ingredients, and dehydrated foods are tested for moisture content to ensure preservation quality, nutritional labeling accuracy, and compliance with purchase specifications, for example under ISO 6496 and GB 5009.3.

Chemicals, Powders, Pigments, and Coatings

Inorganic salts, fillers, catalysts, pigments, coating powders, and fine chemicals are tested for loss on drying and volatile fractions to confirm dryness, packaging condition, and process readiness, following methods such as GB/T 6284.

Testing Items

Accredited third-party laboratories typically offer the following test items within the scope of volatile matter and loss-on-drying analysis:

• Total moisture content of as-received or as-delivered samples
• Moisture in the general analysis sample (air-dried basis moisture)
• Loss on drying (LOD) at specified temperature and duration
• Volatile matter content on air-dried, dry, or dry-ash-free bases
• Residual moisture and volatile content of plastics and polymer pellets
• Volatile-matter content of raw rubber and rubber compounds
• Thermogravimetric compositional profiling (moisture, volatile, combustible, and ash fractions)

Testing Methods

Convection Oven Drying Method

The sample is weighed into a conditioned weighing vessel, dried in a ventilated oven at 105 °C to 110 °C (or at a material-specific temperature) to constant mass, cooled in a desiccator, and reweighed. Loss on drying is calculated as LOD (%) = (m0 − m1) / m0 × 100, where m0 is the initial mass and m1 is the mass after drying. This approach underpins ISO 589, ISO 6496, ASTM D3173, GB/T 211, GB 5009.3, and GB/T 6284, and can be performed in air or under a protective nitrogen atmosphere for oxidation-sensitive materials.

Muffle Furnace Method for Volatile Matter

For coal and coke, a weighed analysis sample is placed in a lidded crucible with a standardized free space, heated at 900 °C ± 10 °C for exactly seven minutes in a muffle furnace, cooled, and reweighed. The percentage mass loss, corrected for the moisture content of the analysis sample, yields the volatile matter. This procedure is specified in ISO 562, ASTM D3175, GB/T 212, and JIS M 8812, with stringent requirements for furnace recovery time, crucible geometry, and placement to ensure reproducibility.

Rapid Moisture Analyzers (Halogen and Infrared Heating)

Balances with integrated halogen or infrared drying units provide fast moisture and LOD results, typically within five to fifteen minutes. They are widely used for in-process quality control and incoming material inspection, and must be validated against the reference oven method for each material matrix.

Thermogravimetric Analysis (TGA)

TGA records mass change continuously while the temperature is programmed through defined atmospheres (nitrogen followed by oxygen, for example), allowing a single run to separate moisture, volatile matter, combustible organic content, and ash. Instrumental proximate analysis based on ASTM E1131, ASTM D5142, and ISO 11358 delivers high throughput and excellent precision, especially for research and comparative material screening.

Applications

Volatile matter and loss-on-drying test results serve a wide range of industrial and regulatory purposes:

• Coal classification, rank determination, combustion modeling, and price settlement in fuel trading
• Coke quality evaluation for blast furnace operation and metallurgical process control
• Incoming resin inspection and melt-processing defect prevention in plastics manufacturing
• Batch release, stability studies, and shelf-life support for pharmaceutical products
• Nutritional labeling, preservation assessment, and supplier qualification for food and feed
• Verification of drying efficiency for rubber, pigments, powders, and specialty chemicals
• Research and development, failure analysis, and comparison of competitive materials
• Compliance demonstration for purchase specifications, certification schemes, and regulatory submissions

FAQ

What is the difference between volatile matter and loss on drying?

Loss on drying measures the mass lost at relatively low drying temperatures (commonly 105 °C to 110 °C), which mainly represents moisture plus very low-boiling volatiles. Volatile matter is determined at a much higher temperature under oxygen-limited conditions and includes all volatile and thermally decomposable constituents, excluding moisture, which is subtracted by calculation.

Which standards govern these tests?

Frequently applied standards include ISO 562, ISO 589, ISO 15512, ISO 248, ISO 11358, ASTM D3173, ASTM D3175, ASTM D5142, ASTM D6980, ASTM E1131, GB/T 211, GB/T 212, GB/T 6284, GB 5009.3, and JIS M 8812. The choice depends on the material type and the specification referenced by the customer or contract.

How much sample is required?

Typical test portions are approximately 1 g for coal volatile matter, 5 g to 10 g for total moisture determinations, and 1 g to 10 g for loss-on-drying tests depending on the material and method. Laboratories generally request additional material to allow for duplicate determinations and repeat testing.

How are results reported?

Results are expressed as mass percentages. For coal, volatile matter may be reported on an air-dried basis (ad), dry basis (d), or dry, ash-free basis (daf), and moisture may be reported on an as-received or analysis-sample basis. Clear basis declaration is essential for correct contractual interpretation.

Why must coal volatile matter crucibles be covered during heating?

The lid restricts air ingress so that released hydrocarbons burn only at the crucible edge, preventing oxidation of the residue. This preserves the definition of volatile matter as decomposition products rather than combusted material, ensuring comparability between laboratories.

Can rapid moisture analyzers replace oven methods?

Rapid analyzers are excellent for routine process control once they have been correlated and validated against the reference oven or furnace method for the specific material. For contractual disputes and certification, reference gravimetric methods performed by accredited third-party laboratories remain the preferred basis.