Not Detected (ND)
Definition
The analyte produced no signal distinguishable from background at the method's limit of detection. It states the limit of what was looked for, not that the substance is absent.
Terms used in this definition
Other entries this definition refers to.
Where this term comes up
Entries whose definition mentions Not Detected (ND).
What this means for research sourcing
Purity and identity verification are central to research reproducibility. Every Volta compound ships with >99% HPLC-verified purity and a certificate of analysis.
Related Terms in Quality
Not Less Than (NLT)
A one-sided specification setting a floor. Purity written as NLT 99.0% is met at 99.0 and failed at 98.9, and nothing above the floor is more compliant than anything else above it.
Not More Than (NMT)
A one-sided specification setting a ceiling, used for things wanted low: single impurities, water content, residual solvents, endotoxin. The pair NLT and NMT is how most certificates express a range.
Specification
The full set of tests and acceptance criteria a material must meet to be released, agreed before manufacture. A certificate reports results; the specification is what makes those results a pass or a fail.
Lot Number
The identifier tying material in a container to the records of how it was made and tested. It is the one field that lets a vial in somebody's hand be matched to the certificate that describes it.
Sample Identification
The unique reference a laboratory assigns to what it received, distinct from the lot number the supplier assigned. A certificate carrying both is traceable from the vial to the bench and back.
Pooled Sample
Material combined from several containers and tested as one. It reports the average and hides variation between them, so a pooled result says less about any individual vial than its purity figure suggests.
Chain of Custody
The documented record of who held a sample, when, and in what condition, from collection to analysis. Without it a result describes a sample whose history cannot be shown, which matters most when the result is disputed.
Audit Trail
The instrument's own tamper-evident log of acquisitions, reprocessing and deletions, with the user and timestamp attached. It is what distinguishes a reported result from the only result obtained.