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Analytical documentation guide

Why a Vial Can Test Above Its Label Claim

A certificate of analysis can list a measured content a little above or below the label. Here is why that happens and what to check on any report.

3-minute readPublished by DAAVY Research

Scope

The short answer

A small gap between the label amount and the measured amount is normal measurement and fill variability. A large gap is the thing to ask about.

This guide describes laboratory documentation for research materials. It is not about human or veterinary use, and research-use-only materials are not approved drugs.

What the report actually shows

One recent NAD+ 1000 mg lot report lists 1009.26 mg by HPLC quantitation against a 1000 mg labeled amount (lot NAD-103026-1000, COA11896). That is about 0.9 percent above the label. Readers often ask whether that means something is wrong. Usually it does not.

Reason 1: every measurement has a spread

No analytical method returns the exact true value. Method validation guidance such as ICH Q2(R2) treats accuracy and precision as measurable properties of an analytical procedure [1]. Accuracy is how close results are to the true value; precision is how close repeated results are to each other. A result close to the label is consistent with a method working normally.

Reason 2: weighing and filling are not perfect

Materials are weighed or filled into vials with a tolerance. FDA has published guidance on excess volume and labeled fill size for injectable vials, which shows fill amounts are a controlled quality topic [2]. That guidance concerns licensed manufacturers of liquid products, so it is context only and not a standard that applies to research materials.

Reason 3: purity and content are different questions

Purity, for example 99.83 percent by RP-HPLC at 214 nm, tells you what share of the detected signal belongs to the main compound. Content tells you how much of that compound is in the vial. A report can show high purity and a content value off the label, or the reverse. Reading only one line leaves half the picture out. The guide on purity vs peptide content explains this in more depth.

What to check on any report

  • The lot number on the report matches the lot on the vial or label.
  • The lab name and report date are present.
  • Identity is confirmed by a separate method, for example LC-MS, not only by purity.
  • The content value is a reasonable distance from the label, and the report says how it was measured.

For more on reading a full report, see the COA decoder and the COA guide.

Limits and risks

One report describes one sample of one lot at one time. It does not prove every vial is identical. Storage, handling and time can change materials after testing. A third-party report is stronger than a self-issued one, but it can still be misread or falsified, which is why matching the lot number matters. This page gives no guidance on use of these materials in people.

References

  1. EMA, ICH Q2(R2) Validation of analytical procedures, scientific guideline.
  2. FDA, Allowable Excess Volume and Labeled Vial Fill Size in Injectable Drug and Biological Products (guidance).
  3. DAAVY NAD+ 1000 mg product page, COA11896, report date November 1, 2026.

References 1 and 2 are regulatory guidance pages, not peer-reviewed articles.