ABSTRACT
Assay is one of the fundamental tests for determining the active ingredient content of a sample. As a general term, assay has come to have various shades of meaning, from simply a synonym for an analytical test to complex extraction procedures to measure the therapeutic levels of a drug in biological matrices. Although there is little regulatory guidance on the de‰nition of assay or how to measure it, assay is mentioned in ICH Harmonised Tripartite Guideline, “Validation of Analytical Procedures: Text and Methodology Q2 (R1),”1 which outlines three major types of analytical tests:
1. IdentiŸcation tests to ensure the identity of an analyte in a sample (e.g., molecular weight measurements and sequencing);
2. Impurity testing as either a quantitative test or a limit test to accurately reªect the purity characteristics in a sample (product-and process-related impurities in oligonucleotides);
3. Assay to quantitatively measure the major component(s) in a drug substance.
