Out of Specification (OOS)
Definition
A result that falls outside an acceptance criterion. It triggers an investigation into whether the measurement or the material is at fault, and an OOS cannot be resolved by simply retesting until a passing number appears.
In more detail
An out-of-specification result opens an investigation rather than closing a question, because at the moment it appears there are two candidate explanations and the data cannot yet separate them: the material does not conform, or the measurement was faulty.
The investigation examines the run before it examines the lot, which is why system suitability, the audit trail and the chain of custody carry weight at exactly this point. What it must not do is retest until a passing number appears. Averaging a failure with later passes, or quietly discarding it, is the practice that regulatory inspection is most alert to.
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
Measurement Uncertainty
The range within which the true value is expected to lie, reported alongside the result. A purity of 99.2% with an uncertainty of 0.4% is not distinguishable from one of 99.5% measured the same way.
Metrological Traceability
An unbroken chain of comparisons linking a result back to a recognised reference, each step with its own stated uncertainty. It is what allows two laboratories using different instruments to be talking about the same milligram.
Measurand
The quantity actually being determined, stated precisely enough to be unambiguous. Peptide content, net peptide content and chromatographic purity are three different measurands on one vial, and they return three different numbers.
Limit of Detection (LOD)
The smallest amount a method can reliably distinguish from background, without being able to say how much is present. A result below it is reported as not detected rather than as zero.
Limit of Quantitation (LOQ)
The smallest amount a method can measure with acceptable accuracy and precision. It is higher than the limit of detection, and a figure reported below it carries more uncertainty than the digits suggest.
Reporting Limit
The lowest value a laboratory will put on a certificate, set at or above the limit of quantitation. Anything smaller is reported against that limit rather than as a number nobody can defend.
Chromatogram
The detector trace a chromatographic run produces: signal against time, with each component appearing as a peak. The purity figure on a certificate is arithmetic performed on the areas of those peaks.
Retention Time
How long a component takes to travel through the column and reach the detector. It is characteristic of a compound under fixed conditions, which is why identity is often confirmed by a sample and a reference standard eluting at the same time.