Analytical Selectivity
Definition
A method's ability to measure the intended analyte without interference from impurities, excipients or degradation products. A purity figure from a method that cannot separate a close-eluting impurity overstates purity.
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
Orthogonal Method
A second method resting on a different physical principle, used to test a result rather than repeat it. Running reversed-phase HPLC and then mass spectrometry is orthogonal; running the same HPLC method twice is not.
Out of Specification (OOS)
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.
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.