If you're new to HPLC or pharmaceutical testing, you might wonder: what’s the difference between an assay and a purity test? While they sound similar, they serve different purposes in quality control.
🧪 What Is an Assay?
An assay measures the amount or potency of the main active ingredient (called the analyte) in a pharmaceutical product. Think of it as answering the question:
“How much of the drug is actually in this tablet or solution?”
Assays are used to confirm that the product contains the correct dosage of the active substance, as stated on the label.
🧼 What Is a Purity Test?
A purity test, on the other hand, focuses on what else is in the sample—specifically, impurities. These can include:
- Related substances (chemically similar compounds)
- Residual solvents ( leftover from manufacturing)
- Degradation products (formed over time)
Purity testing ensures that these unwanted substances are present only in
very small, acceptable amounts.
📘 Why It Matters
Both tests are essential for ensuring drug safety and effectiveness. While the assay confirms the drug delivers the right dose, the purity test ensures it doesn’t contain harmful or excessive impurities.
📚 Want to Learn More?
For more detailed guidance, refer to the International Council for Harmonisation (ICH) guidelines, especially:
- ICH Q2(R2) – Validation of Analytical Procedures
- ICH Q3A/B – Impurities in New Drug Substances and Products
