8.3 Preservation, Custody, and Documentation
Key Takeaways
- Preservation slows specified changes after collection; it cannot repair contamination, a wrong sampling point, or an expired holding time.
- Container, preservative, temperature, light protection, headspace, and holding time are analyte-and-method specific and must come from the current plan and laboratory instructions.
- Holding time begins at collection and ends at the preparation or analysis step defined by the applicable method, so transport plans must leave the laboratory enough time.
- Complete labels, field records, custody transfers, receipt-condition checks, and deviation records make a sample result traceable and defensible.
Preserve the condition—not merely the bottle
Once water leaves the process, its chemistry and biology can continue changing. Preservation applies method-approved controls that slow a specified change long enough for valid preparation or analysis. Cooling may slow reactions and biological activity; a chemical preservative may adjust pH, neutralize a disinfectant, or stabilize a target analyte; an opaque container may protect a light-sensitive constituent; eliminating headspace may limit loss of volatile compounds. None of these actions makes every analyte permanently stable.
Preservation also cannot correct a bad sample. Acid does not make a stagnant tap representative. Cooling does not remove contamination introduced by a dirty cap. A custody seal does not restore a missed holding time. On WPI application questions, separate four controls: correct collection, correct preservation, controlled possession, and complete documentation. A sample needs all controls required by its purpose.
| Integrity control | Governing question | Example of a method-dependent decision |
|---|---|---|
| Container | Will the bottle add, lose, or alter the target? | Plastic, glass, sterile bottle, or volatile-organic vial |
| Preservative | What change must be slowed or stopped? | Cooling, acid, disinfectant neutralizer, or none |
| Filling technique | Is rinsing or headspace allowed? | Preserved/sterile bottles often are not rinsed; volatile samples may require no bubbles |
| Holding time | By when must the defined preparation or analysis occur? | Immediate field analysis for an unstable parameter versus later laboratory work |
The current analytical method, approved monitoring or sampling plan, laboratory instructions, and applicable regulator determine these details. Never create a universal table from memory. EPA's drinking-water sampling guide illustrates why: its procedures differ for bacteriological, inorganic, disinfectant-residual, metal, synthetic-organic, and volatile-organic samples, and it repeatedly directs samplers to confirm requirements with the analyzing laboratory.
Build the transport plan backward from the deadline
Holding time starts at sample collection, not when the courier arrives or when the laboratory logs in the cooler. Its endpoint is the preparation or analysis event specified by the method. Before leaving the plant, work backward: laboratory operating hours, receipt and login time, sample preparation, travel, courier cutoff, and a delay margin must all fit. Ship today is not proof that the sample can be processed on time.
EPA's guide lists disinfectant-residual colorimetry as immediate onsite analysis, while other analytes can travel under method-specific conditions. The contrast teaches the principle; it does not create a rule for another analyte. Reconfirm supplies and timing whenever the method or laboratory changes.
Preservatives can be hazardous. Use the specified protective equipment and correctly identified supplies. Do not rinse a bottle that already contains preservative. If field addition is permitted, follow and record the exact instruction. Maintain the required temperature, light, and orientation conditions while protecting caps and labels from damage.
Create one traceable identity
Assign a unique sample ID linked to the bottle and record. Document site, collection date/time, sampler, purpose, requested analyses, collection method, container, preservative, and relevant field observations. Record deviations or conditions that affect interpretation. Correct errors under the documented record practice; never erase or reconstruct facts from memory.
A chain-of-custody (COC) record adds possession history when required. It identifies samples and requested work, then records each relinquishment and receipt with names or signatures and date/time. Applicable procedures define control through possession, observation, secured containers, or restricted storage. Document seal numbers and condition when seals are used. Routine sample tracking remains necessary even when formal evidentiary custody is not.
Laboratory receipt is a quality gate
At receipt, the laboratory compares bottle labels with the submission record and checks arrival time, container and seal condition, preservation evidence, required temperature or other receipt checks, sufficient volume, and the remaining holding-time window. A leaking bottle, broken seal, missing ID, incorrect container, or exceeded method limit is a deviation—not an invitation to silently repair the paperwork. The laboratory follows its sample-acceptance policy: accept, qualify, reject, or request recollection as authorized, while documenting the decision and notifying the appropriate person.
Application scenario: the delayed cooler
A courier delay leaves little or no time before the method's endpoint. Changing the collection time, adding preservative late, or requesting unqualified analysis cannot restore integrity. Preserve the real timeline, notify the laboratory and responsible program role, document receipt conditions, and apply the acceptance policy. The monitoring plan or authority determines whether recollection meets the original obligation.
A missing custody signature is a separate traceability deviation. Fixing a form does not restore an expired time, and timely analysis does not erase a custody gap. Identify both defects, protect the result from unsupported use, notify appropriately, and prevent recurrence through scheduling and pre-departure checks.
Pre-transfer check
- Match every bottle ID to the form and requested analysis.
- Confirm cap, seal, preservative indicator, and required storage condition.
- Record collection time and field observations while they are fresh.
- Calculate the latest usable receipt/preparation/analysis schedule from the method.
- Sign and time each custody transfer when formal COC applies.
- Give the laboratory prompt notice of delays, damage, or deviations.
Official source trail
A preserved sample reaches the laboratory after the applicable method's holding time has expired. Which response is most defensible?
What information is most important when custody of samples is transferred to a courier?
Which statement about sample preservation is correct?