Source of Chain of custody

{{Infobox method | name = Chain of custody | subtitle = Sampling discipline | Records = Who held the sample, when, and under what conditions | Purpose = Excludes substitution, tampering and undocumented excursion | Pairs with = [[Blind sampling|Blind sampling]] }} A '''chain of custody''' is the documented sequence of individuals who held a sample between the moment it was drawn and the moment it was analysed, together with the conditions under which it was held and the transfers between them. Its purpose is to exclude substitution, tampering and undocumented storage excursions as explanations for a result.{{r|iso17025}} In the context of peptide testing, an unbroken chain of custody is uncommon. Most independent reports arise from material bought, shipped, stored for an unknown period and then submitted, with no documentation of any of it. This does not make the results worthless; it bounds what they can establish.{{r|reports}} Chain of custody is complementary to [[Blind sampling|blind sampling]]. Blind sampling addresses selection — whether the sample was chosen to be favourable. Chain of custody addresses handling — whether the sample analysed is the sample drawn, unchanged. == What the record contains == A chain-of-custody record identifies the sample uniquely, names each person who held it with the dates of transfer, and states the storage conditions maintained at each stage. Where temperature matters, a record without temperature is incomplete.{{r|iso17025}} For peptides, temperature and time are the conditions that matter most, because the degradation routes — [[Deamidation|deamidation]], [[Methionine oxidation|oxidation]], [[Peptide aggregation|aggregation]] — are all time- and temperature-dependent. A sample held at ambient temperature for three weeks before analysis may return a lower purity than the same material analysed on receipt, and without a record it is impossible to attribute the difference.{{r|usp1503,ich_q1a}} This is the single most common confound in community testing. A result reported as characterising a supplier's material may be characterising the purchaser's storage, and the two are indistinguishable without a custody record. See [[Temperature excursion]]. == Why it is usually absent == The ordinary sequence for a community-submitted report is: material is bought; it is shipped by a carrier under unknown conditions; it is received and stored by the purchaser for some period; a vial is selected; it is posted to a laboratory. No step in that sequence is documented in a way that would satisfy a custody requirement.{{r|reports}} The consequences run in both directions and are not symmetric in the way people usually assume. Degradation in transit or storage produces a result worse than the material as shipped, so an unfavourable result from an uncontrolled chain is weak evidence against a supplier. A favourable result is less affected, since degradation does not improve purity — but it says nothing about whether that vial was representative. The practical upshot is that uncontrolled-chain results are more informative when favourable than when unfavourable, which is the reverse of how they are usually read. == Approximations available in practice == Full custody documentation is not achievable for community testing, but several partial measures narrow the gap and appear in submissions to this wiki.{{r|reports}} | Measure | What it excludes | |---|---| | Analysis on receipt, unopened | Purchaser storage | | Temperature indicator in the shipment | Undocumented transit excursion | | Sending direct from supplier to laboratory | Purchaser handling entirely | | Photographing the sealed vial before dispatch | Substitution after receipt | | Retaining a second unit unopened | Allows re-analysis if disputed | Direct supplier-to-laboratory shipment is the strongest of these, and it also converts an unblinded submission into something closer to [[Blind sampling|blind sampling]] if the supplier is not told the destination is a laboratory. Whether that is achievable depends on the transaction and is not always possible. None of this makes an uncontrolled result useless. It makes explicit what the result is evidence for, which is the aim.{{r|iso17025}} == References == {{reflist}} <ref name="iso17025">ISO/IEC 17025:2017, ''General requirements for the competence of testing and calibration laboratories'', clause 7.4 (handling of test items).</ref> <ref name="reports">PeptidePedia Wiki community test-report tally, 2024–2026 (self-reported; see [[Project:Sourcing_guidelines]]).</ref> <ref name="usp1503">United States Pharmacopeia, General Chapter <1503>, ''Quality Attributes of Synthetic Peptide Drug Substances''.</ref> <ref name="ich_q1a">International Council for Harmonisation, ''Q1A(R2): Stability Testing of New Drug Substances and Products'' (2003).</ref> == See also == * [[Blind sampling]] * [[Third-party testing]] * [[Temperature excursion]] * [[Lot traceability]] * [[Cold chain]] {{DEFAULTSORT:Chain of custody}} [[Category:Testing methodology]] [[Category:Traceability]] [[Category:Quality and testing]]