VOC Content EPA Method 24

Reviewed by SEMI Gr

EPA Method 24: VOC Content of Surface Coatings

The air quality regulation defines the permissible limit for volatile organic compounds in the coating, measured in grams per liter. EPA Method 24 determines this amount, and it is not a single measurement. It consists of several determinations, and the results are added together. This means a mistake in any one determination will affect the VOC figure.
MatX Lab determines VOC content in paints, varnishes, lacquers, inks, adhesives, and related coatings.

What Method 24 Determines

This technique measures the content of volatiles, moisture, density, volume solids, and weight solids of the surface coating. The amount of VOCs in the coating is then calculated using the data obtained.
The principle is subtraction. This technique measures the total volatile matter, subtracts moisture content and regulatory-exempt compounds, and determines the amount of VOCs.
The applicable volume basis depends on the regulation. VOC per liter of coating, per liter of coating less water, and per liter of solids are all used, and they produce very different numbers for the same coating. A VOC figure quoted without its basis cannot be compared against a limit.

The Component Determinations

Each of these is a full determination in its own right with its own sources of error, which is why a Method 24 result takes longer and costs more than the single number suggests.
Water determination carries particular weight for waterborne coatings, where water may make up most of the volatile fraction. A percentage-point error in water content can substantially shift the VOC result for a low-VOC waterborne product, which is exactly the category where the regulatory limit is tightest.

Multicomponent Coatings

Two-component and multicomponent systems are prepared according to the manufacturer’s mixing instructions before analysis, and this is where compliance frequently goes wrong.

The mixing ratio determines the VOC content of what is actually sprayed. A coating compliant as supplied can become non-compliant once thinned, and if the regulation applies to the coating as applied, the formulator’s recommended thinning must be included in the analysis.
Induction time and pot life are important factors. If the system keeps reacting after mixing, the amount of volatiles after five minutes will differ from what it is after thirty minutes.

Tell us the full mixing and thinning instruction at submission, including the maximum recommended thinner addition, because a regulator will ask about the worst case rather than the best.

Exempt Compounds

Some volatile organic compounds are not included in the VOC definition in the regulations because their photo reactivity is negligible. Among such VOCs are acetone, some halogenated solvents, and many fluorinated compounds.

When calculating VOC content, these exempt compounds are excluded from the total volatile matter, along with water. This reduces the reported VOC value even if the coating still contains the same overall amount of volatile material.

Two important points are worth considering. Using exempt solvents as part of a reformulation is an accepted way for manufacturers to meet VOC requirements and is commonly used across the industry. However, exemption lists vary by region and can change over time. A coating that meets VOC requirements in one region may not meet them in another, and a formulation that was previously compliant may no longer qualify under a later version of the regulations.

Identify exempt compounds present in the formulation at submission. The analysis quantifies what there is; deciding what counts as exempt is a regulatory question that depends on where the product is sold.

Precision and Its Limits

Method 24 is known to have relatively poor precision on low-VOC coatings, and this is a practical problem rather than an academic one.
The reason is structural. When VOC is a small difference between two large numbers, total volatiles and water, the relative uncertainty on that difference is large. A coating at 50 g/L carries far more proportional uncertainty than one at 400 g/L.
One way to estimate VOC content is to determine it from the paint formulation, using the formulation to estimate the expected VOC content. Sometimes regulators allow this procedure, while sometimes they mandate Method 24.

If a coating is close to the applicable limit, it is better to replicate tests and clearly report the uncertainty of the result than to rely on one figure that may appear more precise.

Sample Requirements

Supply coating in its original sealed container with the batch identification and the full technical data sheet.
For multicomponent systems, provide all components in their specified proportions, including the recommended thinner. Please also include the mixing instructions and the stated pot life.

You will need more material than you might expect because the testing involves several separate determinations, and each requires its own sample. For a single-component product, send at least one liter. For multicomponent systems, provide a proportionally larger amount.

State the regulation and jurisdiction the result must serve, since the volume basis and the exempt compound list both follow from it.