Volatile Matter Content Determination Comparison Experiment: Standards, Methods, and Result Evaluati

A volatile matter content determination comparison experiment is a systematic interlaboratory or inter-method study used to verify the accuracy, repeatability, and reproducibility of volatile matter measurements on materials such as coal, coke, biomass, plastics, and coatings. By testing identical homogenized samples under standardized conditions specified in ISO, ASTM, EN, and GB standards, laboratories can quantify bias, validate operating procedures, and demonstrate technical competence. This article explains the testing principle, sample types, experimental methods, statistical evaluation criteria, and typical industrial applications of volatile matter comparison experiments.

Technical Overview

Volatile matter is defined as the mass loss, excluding moisture, that a material releases when heated under strictly controlled conditions of temperature, time, atmosphere, and container geometry. It is one of the four components of proximate analysis, alongside moisture, ash, and fixed carbon, and it directly reflects the thermal decomposition behavior, combustion characteristics, and processing stability of fuels and polymeric materials.

A volatile matter determination comparison experiment (comparison testing) involves distributing the same homogenized test samples to different laboratories, operators, instruments, or analytical methods, and then comparing the resulting data against reference values or statistically derived consensus values. The primary objectives of such an experiment include:

• Verifying the accuracy and trueness of a laboratory's routine volatile matter results
• Quantifying between-laboratory bias and within-laboratory repeatability
• Validating the equivalence of alternative methods, such as muffle furnace gravimetry versus thermogravimetric analysis
• Supporting internal quality control programs and proficiency testing participation with accredited third-party laboratories
• Providing a defensible technical basis for resolving commercial or contractual disputes

Testing Samples

Coal and Coke

Bituminous coal, anthracite, lignite, blended thermal coal, coking coal, and metallurgical coke are the most common subjects of volatile matter comparison experiments. Because coal is heterogeneous, samples are air-dried, crushed, and ground to an analysis fineness of 0.2 mm or finer before subsampling, so that all participants receive chemically identical material.

Solid Biomass Fuels

Wood pellets, wood chips, straw, rice husk, and other agricultural residues are tested to characterize devolatilization behavior relevant to combustion and gasification. Biomass samples are particularly moisture-sensitive and must be stored in airtight containers prior to the comparison test.

Plastics and Polymer Materials

PVC resin, polyolefin powders, engineering plastics, masterbatches, and recycled polymer feedstocks are compared to verify residual monomer, moisture, and processing-additive loss, which affects melt stability and product quality.

Coatings, Inks, and Rubber Materials

Liquid coatings, printing inks, and raw or compounded rubber are tested for volatile content to control drying behavior, solvent release, shelf stability, and regulatory compliance.

Testing Items

The comparison experiment typically covers the following determination and evaluation items:

• Volatile matter content on an air-dried basis, dry basis, and dry ash-free basis
• Absolute and relative deviations between paired results from different laboratories or methods
• Simultaneous moisture and ash determinations required to correct and normalize the volatile matter result
• Statistical indicators including mean values, standard deviations, En numbers, and z-scores
• Assessment against the repeatability and reproducibility limits stated in the governing standard

Testing Methods

Reference Gravimetric Method (Muffle Furnace)

For coal and coke, the reference procedure follows ISO 562, ASTM D3175, and GB/T 212. A 1 g ± 0.1 g specimen is placed in a lidded platinum, quartz, or ceramic crucible, and the covered crucible is introduced into a muffle furnace already stabilized at 900 °C ± 10 °C for exactly 7 minutes. The crucible is then cooled in a desiccator and reweighed. Volatile matter is calculated as the percentage mass loss minus the independently determined moisture content. The lid is essential because it restricts air ingress and prevents oxidation of the residue, which would otherwise depress the result.

Thermogravimetric Analysis (TGA)

Thermogravimetric analyzers, applied in accordance with ISO 11358 for polymers, provide automated mass-loss curves under programmed temperature ramps and controlled atmospheres. When TGA results are compared with muffle furnace data, the method-equivalence study must account for differences in heating rate, purge gas, and sample mass, and acceptance is judged against predefined tolerance limits.

Low-Temperature Oven Method

For coatings (ISO 3251), PVC resin (ISO 1269), and rubber (ISO 248), volatile matter is determined by heating a specified specimen, spread in a thin layer, at approximately 105 °C for a defined period and measuring the gravimetric loss. These low-temperature procedures are frequently included in cross-laboratory comparisons because small deviations in temperature, time, or specimen geometry can produce significant bias.

Comparison Experiment Procedure

• Prepare a master sample by homogenizing, grinding, and riffle-splitting the material into coded, equal-mass subsamples
• Distribute subsamples simultaneously to all participating laboratories together with a written test instruction sheet
• Require duplicate determinations from each participant under the designated reference standard
• Determine moisture in parallel so that volatile matter can be reported on a consistent basis
• Collect results within an agreed timeframe, perform outlier screening, and evaluate deviations statistically

Result Evaluation Criteria

Evaluation combines standard-based limits and statistical tools. For hard coal, GB/T 212 and ASTM D3175 specify repeatability limits of approximately 0.3 to 0.5 percent absolute within a laboratory and reproducibility limits of approximately 0.5 to 1.0 percent absolute between laboratories, depending on the volatile matter level. For interlaboratory schemes conducted in accordance with ISO 13528, the following performance indicators are commonly applied:

• An En number with an absolute value of 1 or less indicates a satisfactory result; values exceeding 1 indicate a significant deviation from the reference value
• A z-score of 2 or less is satisfactory, values between 2 and 3 are questionable, and values of 3 or greater are unsatisfactory
• Paired t-tests or F-tests may be used to assess the significance of systematic bias and precision differences between two laboratories or two methods

Applications

• Coal trading and price settlement, where volatile matter is a contractual specification for combustion behavior and coking performance
• Power plant boiler and gasifier operation, where devolatilization data guide flame stability, burner adjustment, and fuel blending decisions
• Coke oven and metallurgical process control, where volatile matter governs charge balance and by-product yield
• Biomass fuel quality certification and supplier qualification programs
• Plastics manufacturing, for verifying resin drying efficiency and residual volatile levels before extrusion or molding
• Coating and ink formulation, for controlling solvent release and volatile organic content
• Laboratory quality assurance, including method validation, periodic verification against certified reference materials, and participation in proficiency testing schemes organized by accredited third-party laboratories
• Third-party arbitration when disputed analytical results require an independent, statistically supported comparison

FAQ

What is the purpose of a volatile matter comparison experiment?

Its purpose is to objectively confirm that volatile matter results produced by a given laboratory, instrument, operator, or method agree with reference or consensus values within acceptable limits, thereby demonstrating accuracy, controlling measurement risk, and identifying the causes of any systematic bias.

Why is the crucible covered during coal volatile matter determination?

The lid restricts the ingress of air so that released volatiles escape rather than ignite, and it prevents oxidation of the hot char. An uncovered or poorly seated lid changes the atmosphere inside the crucible and typically produces low, non-repeatable results.

What deviation between two laboratories is considered acceptable?

For coal and coke tested to ISO 562, ASTM D3175, or GB/T 212, between-laboratory agreement within approximately 0.5 to 1.0 percent absolute, depending on the volatile matter level, is generally considered acceptable, provided each laboratory first meets its own repeatability requirement.

How are thermogravimetric results compared with muffle furnace results?

Identical subsamples are analyzed by both techniques, and the paired data are assessed using relative deviation, regression analysis, and the tolerance limits of the reference method. Systematic offsets arising from heating rate, purge atmosphere, and specimen mass are documented, and a correction or an expanded acceptance interval is established where equivalence is demonstrated.

How should samples be prepared to guarantee comparability?

All participants must receive material from a single homogenized batch, ground to the fineness required by the reference standard, split using unbiased dividers, sealed in airtight containers, and tested promptly so that moisture pickup or loss cannot distort the comparison.

What statistical criteria conclude the comparison?

The experiment is concluded successfully when all reported values pass outlier screening and satisfy the applicable En number or z-score criteria under ISO 13528, and when every laboratory's duplicate determinations remain within the repeatability limit of the governing standard.