Difference Between LOD (Loss on Drying) and Moisture Content Analysis
🔹 Introduction
In quality control and analytical laboratories, determining moisture content is one of the most important routine tests.
Both Loss on Drying (LOD) and Moisture Analyzer methods are used to estimate the amount of water present in a sample — but they are not the same.
While both help assess product stability, shelf life, and processing performance, they differ in principle, purpose, and accuracy.
Let’s understand how.
1️⃣ What Is LOD (Loss on Drying)?
Definition:
LOD is a gravimetric method used to determine the total amount of volatile substances (mainly water) that evaporate when a sample is heated under specified conditions.
In simpler terms, LOD tells us how much weight a sample loses after drying, which represents its moisture + volatile content.
⚙️ Purpose of LOD
✔️ Measures moisture and volatile solvents/compounds
✔️ Used in pharmaceuticals, food, and chemical testing
✔️ Helps ensure product stability, quality, and compliance
🔬 How It Works
- A sample is weighed accurately before drying.
- It is then heated in an oven (commonly at 105°C for 2 hours, or as per pharmacopeia).
- The sample is cooled in a desiccator and weighed again.
- The difference in weight gives the Loss on Drying (%).
LOD (%)= Initial weight − Final weight × 100 / Initial weight
📗 Regulatory Relevance
LOD is an official pharmacopeial method accepted by USP, EP, BP, and IP, making it the reference standard for determining total volatiles.
2️⃣ What Is a Moisture Analyzer?
Definition:
A moisture analyzer (also known as a halogen moisture balance) is an instrument that measures moisture content only by drying a sample and continuously recording its weight loss in real time.
⚙️ Purpose of a Moisture Analyzer
✔️ Measures moisture only, not other volatiles
✔️ Ideal for in-process control and routine QC testing
✔️ Provides fast and convenient moisture results
🔬 How It Works
- A small sample is placed on the analyzer’s built-in weighing pan.
- The instrument uses a halogen or infrared heating source to dry the sample.
- As the sample dries, real-time weight loss is measured.
- Once the weight stabilizes, the moisture percentage is displayed automatically.
This process usually takes 2–10 minutes, depending on the sample type and drying program.
⚙️ Regulatory Note
While moisture analyzers provide quick results, they are not always pharmacopeia-approved for official product release unless validated against LOD.
Key Differences Between LOD and Moisture Analyzer
| Feature | LOD (Loss on Drying) | Moisture Analyzer |
|---|---|---|
| Type | Analytical method (manual) | Instrument/device (automated) |
| Measures | Moisture + volatile substances | Moisture only |
| Equipment | Oven + analytical balance | Compact halogen/infrared device |
| Time Required | 30 min – 2 hours | 2 – 10 minutes |
| Accuracy Depends On | Method, drying conditions, sample handling | Calibration and drying program |
| Pharmacopeial Status | Official method (USP/EP/IP) | Typically used for rapid testing or in-process control |
🔍 When to Use Which?
- Use LOD when regulatory or pharmacopeial compliance is required, such as during final product release or stability testing.
- Use Moisture Analyzer for routine monitoring, in-process control, or quick checks during manufacturing.
Both techniques can complement each other — LOD ensures accuracy, while moisture analyzers ensure speed.
💡 Final Thoughts
Although both LOD and moisture analyzers measure water content, they serve different purposes.
LOD provides a comprehensive measure of all volatiles — the gold standard for regulated testing.
The moisture analyzer, on the other hand, offers rapid and practical results for day-to-day operations.