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Laboratory
All Containers›Shop by use case›Laboratory›The container›Why the material changes the resultShop all laboratory →
The container

Why the material changes the result

By Dwight Davis, Founder

Updated

On this page7
A container interacts with what is in it three ways, and all three move the number in a direction nobody downstream can see.

Leaching: the container adds something

Material migrates out of the wall into the sample. Glass can contribute sodium, boron and silica; plastics can contribute plasticizers and trace metals from processing. If you are measuring something at trace level and the bottle supplies it, the result is high and looks real.

Adsorption: the container removes something

Analytes stick to the wall and leave solution. Metals at low concentration are the classic case, which is why acid preservation is specified for them: it keeps them in solution rather than on the glass. Organics adsorb onto plastics the same way.

Permeation: the container lets something through

Gases and volatile organics pass through plastic walls in both directions over time. A volatile sample in a permeable bottle loses analyte to the air; a clean sample stored near solvents can gain it. Glass and fluoropolymer are the answer where this matters.

Which is why the regulation names the material

Table II does not say "a suitable container". It gives codes, and footnote 1 defines them: P for polyethylene, FP for fluoropolymer, G for glass, PA for a sterilizable plastic, LDPE for low density polyethylene. The regulation is specifying the polymer.

Clean is a specification too

For trace work the container has to arrive at a known cleanliness, and certified pre-cleaned containers exist for exactly that. Washing a bottle yourself and assuming it is clean enough for trace metals is a common and invisible error.

None of this announces itself

A leached, adsorbed or permeated sample looks completely normal. There is no cloudiness, no smell, no sign. That is the reason the container is specified in advance rather than judged afterwards.

References

40 CFR 136.3, Table II — Required Containers, Preservation Techniques, and Holding Times, which prescribes the container material, the preservation and the maximum holding time per parameter. Footnote 1 defines the codes: “P” is polyethylene, “FP” is fluoropolymer (PTFE), “G” is glass, “PA” is any plastic made of a sterilizable material. law.cornell.edu
Written from federal regulation, not from a bench. Where a method specifies a container, a preservative or a holding time, the method governs and nothing here overrides it. Read the method you are running rather than a summary of what methods generally say.