A test result is only as reliable as the method behind it. In regulated laboratories, methods are formally validated, meaning shown by experiment to be fit for their purpose, before their results are trusted.
The international standard
The core reference is the ICH guideline Q2 on the validation of analytical procedures, revised as Q2(R2) in 2023. It's used by regulators including the MHRA, EMA and FDA. It defines the characteristics a method must be tested against.
Key validation characteristics
| Characteristic | Question it answers |
|---|---|
| Specificity | Can the method tell the target apart from impurities, degradation products and the matrix? |
| Linearity and range | Is the response proportional to concentration across the levels that matter? |
| Accuracy | How close are results to the true value, e.g. when a known amount is added? |
| Precision | How close are repeated results to each other: same day (repeatability), different days, analysts or instruments (intermediate precision), and different labs (reproducibility)? |
| Detection limit (LOD) | What is the smallest amount that can be detected? |
| Quantitation limit (LOQ) | What is the smallest amount that can be measured reliably? |
| Robustness | Do small, deliberate changes to temperature, pH or flow rate change the result? |
System suitability: checking every run
Even a validated method has to be shown to work on the day. System suitability tests are run with each batch of samples, checking things like peak resolution, peak symmetry and how reproducible repeated injections of a standard are. If the system fails, the results from that run aren't reported.
Reference standards
Accurate quantity measurements need a well-characterised reference standard of the same compound. Without one, a lab can still report area-percent purity, but it can't make a reliable statement about the absolute amount of peptide present.
Accreditation
Laboratories can be accredited to ISO/IEC 17025, the international standard for testing and calibration labs. In the UK accreditation is granted by UKAS. Accreditation applies to a specific scope of tests, so it's worth checking that the test you care about is actually covered. Pharmaceutical quality-control labs also work under Good Manufacturing Practice.
Key takeaway: when comparing results from different labs, ask whether the method was validated, what its limits are, and whether the lab is accredited for that test. Two "99% pure" results from different methods aren't necessarily the same.
Related articles
- D-amino acids and peptidomimetics
- Why some peptides are hard to make
- Mass spectrometry explained for peptides
Sources and further reading
- International Council for Harmonisation. Quality guidelines, including Q2(R2) Validation of Analytical Procedures. www.ich.org/page/quality-guidelines
- United Kingdom Accreditation Service (UKAS). www.ukas.com