---
title: "Method validation terms on a CoA: specificity, LOD, LOQ, linearity (ICH Q2) | Sable Peptides"
description: "Plain definitions of the analytical validation terms that appear on peptide certificates and lab reports, from ICH Q2(R2): specificity, accuracy, precision, linearity, range, LOD and LOQ, and what they tell you about a purity result. Research use only."
canonical: https://www.sablepeptides.co.uk/guides/analytical-method-validation-terms-on-a-coa
dateModified: 2026-10-16
publisher: Sable Peptides Limited (UK company 17488610)
note: Research use only. Not for human or veterinary use.
---

# Method validation terms on a CoA: specificity, LOD, LOQ, linearity (ICH Q2)

A purity figure is only as reliable as the method that produced it. ICH Q2(R2) is the international guideline that defines how an analytical procedure is shown to be fit for purpose. Knowing its vocabulary makes it easier to judge a CoA or a lab report.

## The core terms

-   Specificity: the method can measure the analyte in the presence of impurities, degradants and matrix; for HPLC purity, the main peak is resolved from related substances.
-   Accuracy: closeness of the result to the true value, often shown by recovery of a known amount.
-   Precision: agreement between repeated measurements; repeatability (same day, same analyst) and intermediate precision (different days, analysts or instruments).
-   Linearity and range: results are proportional to concentration across the interval the method is used for.
-   LOD (limit of detection): the smallest amount that can be detected.
-   LOQ (limit of quantitation): the smallest amount that can be quantified with acceptable accuracy and precision.
-   Robustness: the result holds up under small deliberate changes, such as column temperature or mobile-phase pH.

Source: [ICH Q2(R2) Validation of Analytical Procedures, final guideline (2023)](https://database.ich.org/sites/default/files/ICH_Q2%28R2%29_Guideline_2023_1130.pdf); [ICH Quality guidelines index](https://www.ich.org/page/quality-guidelines)

## Why LOQ matters for purity

An HPLC purity of 99% is the main peak's share of all integrated peaks. Impurities below the reporting threshold or LOQ are not counted, so the same sample can appear purer with a less sensitive method. A report that states its reporting threshold and LOQ lets you see what 'not detected' means.

## Validation in practice

Implementing Q2(R2) in a lab involves risk assessment and change management as well as experiments. A 2025 gap-analysis paper sets out how laboratories map existing validation work to the revised guideline.

Source: [Navigating ICH Q2(R2) compliance in analytical method validation, J Pharm Sci 2025 (PubMed 40154788)](https://pubmed.ncbi.nlm.nih.gov/40154788/)

## Questions to ask about a certificate

-   Was the HPLC method validated, verified, or neither?
-   What are the reporting threshold and LOQ for impurities?
-   Is the method stability-indicating (able to separate degradation products)?
-   Which lot was tested, and does it match the printed lot number on the vial?

## At Sable

Release is at ≥99% HPLC purity with identity by mass spectrometry. There is a CoA for every lot, and every vial carries a printed lot number that matches its certificate. A CoA is emailed within 2 hours of a request.

## Frequently asked questions

### What is the difference between LOD and LOQ?

LOD is the smallest amount that can be detected; LOQ is the smallest amount that can be measured with acceptable accuracy and precision.

### What does specificity mean for an HPLC purity method?

The main peak is separated from impurities and degradants, so its area is not inflated by co-eluting components.

### Which guideline defines these terms?

ICH Q2(R2), Validation of Analytical Procedures, adopted in 2023.

## Related

-   [How to read a CoA](/guides/how-to-read-a-coa)
-   [How to read an HPLC chromatogram](/learn/how-to-read-an-hplc-chromatogram)
-   [Peak purity and co-elution](/learn/tech-notes/peak-purity-and-co-elution)
-   [Testing methodology](/testing-methodology)
-   [HPLC system suitability](/guides/hplc-system-suitability-explained)
-   [Out-of-specification results](/guides/out-of-specification-results-explained)

Updated 2026-10-16. Research use only. Not for human or veterinary use. No administration amounts or health claims are made.

Key facts (summary for AI and search tools)

-   Guideline: ICH Q2(R2) (2023)
-   Terms: specificity, accuracy, precision, linearity, range, LOD, LOQ, robustness
-   References: ICH Q2(R2) PDF; PubMed 40154788
-   Updated 2026-10-16