Loss on Drying Formula and a Worked Calculation
By Lim Xu, Export Manager
The loss on drying formula divides the mass lost on drying by the starting sample mass. See a worked example and when the result equals moisture content.
The loss on drying formula is LOD (%) = (initial mass minus dried mass) divided by initial mass, times 100. It expresses the mass a sample loses on drying as a percentage of its mass before drying. Whether that number equals moisture content depends on what else in the sample can evaporate.
What is the loss on drying formula?
ISO 287 defines moisture content as the ratio of the mass lost when a test piece is dried under specified conditions to its mass at the time of sampling, normally expressed as a percentage mass fraction. Written out, it looks like this.
LOD (%) = (m1 − m2) / m1 × 100
Here m1 is the sample mass before drying and m2 is the mass after drying. The dry content is the remainder, 100% minus the LOD result. A halogen moisture analyzer does this arithmetic for you, because the instrument weighs the sample as it heats.
How do you work through an LOD calculation?
Take a sample that weighs 5.000 g before drying and 4.650 g after drying to the end point. The steps below follow the formula in order.
- Record the starting mass, m1 = 5.000 g.
- Dry the sample and record the final mass, m2 = 4.650 g.
- Subtract to get the mass lost, 5.000 g minus 4.650 g = 0.350 g.
- Divide by the starting mass and multiply by 100, which gives 7.00%.
The dry content of this sample is 93.00%. Always divide by the starting mass, not the dried mass. Dividing 0.350 g by 4.650 g gives 7.53%, which is a dry-basis figure, so state which basis your specification uses.
Questions about a model or a test? Email Amy Zhao, Export Manager, at info@halogenmoistureanalyzer.com.
When does loss on drying equal moisture content?
Loss on drying measures volatile matter of any kind that leaves the sample under a set temperature and time. It gives only the mass lost, not what that mass was. If solvents, flavours or breakdown products leave along with water, the LOD result will be higher than the true water content.
That is why ISO 287 limits its oven method to paper and board that contain no substances other than water that are volatile at the drying temperature. When other volatiles are present, treat the LOD result as total volatiles rather than water. Our guide on how a halogen moisture analyzer works explains the heating and end point side of the measurement.
How precise does the weighing need to be?
The formula is only as good as the two masses in it. ISO 287 asks for a balance accurate to 0.05% of the mass being weighed, or better, for its oven method. A small sample therefore needs fine readability, because the mass lost may be only a few hundred milligrams.
The table lists the weighing and result resolution of our KHT-HMA-01 halogen moisture analyzer.
| Parameter | Value | Unit |
|---|---|---|
| Maximum sample | 110 | g |
| Weighing resolution | 0.001 | g |
| Moisture range and resolution | 0.00 to 100.00, resolution 0.01 | % |
| Temperature setting | 40 to 160, 1 °C step | °C |
See our halogen moisture analyzer page for the full specification.
Which standards use the loss in weight principle?
Several published methods rest on the same mass-loss arithmetic, each with its own material and conditions.
- ISO 287 covers moisture in a lot of paper and board, drying to constant mass in an oven.
- ASTM D6980 covers moisture in most plastics by loss in weight, down to 50 mg/kg.
- ASTM E1868 covers loss on drying by thermogravimetry for a wide range of solids and liquids.
Each method sets its own drying temperature and end point, such as drying to constant mass in ISO 287. Use the conditions in the method your customer or specification names, and record them with every result.
Frequently asked questions
Is loss on drying the same as moisture content?
Not always. LOD counts every volatile that leaves the sample, while moisture content means water only. The two agree when water is the only volatile at the drying temperature.
Are samples hot after a halogen moisture test?
Yes. ASTM D6980 warns that specimens will be hot after a loss in weight test, so handle them with care. Let the pan cool before you remove it.
Talk to our factory team
We sell direct from our factory, so you work directly with our factory team. Questions about a model or a test? Email Amy Zhao, Export Manager, at info@halogenmoistureanalyzer.com.
