The container decision, as a checklist
Updated
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The six
- Does a method apply? If yes, read it first; it may name the container and nothing here overrides it.
- Which analyte? Table II is organized by parameter, and one sampling visit may need several container types.
- Organic, volatile, or trace inorganic? That picks between glass, fluoropolymer-faced and polyethylene.
- What preservative? It decides what the container and the liner must tolerate for the holding time.
- Sterile, autoclaved, or neither? Sterility narrows the material sharply.
- What volume, and any headspace rule? Zero headspace is a container and closure requirement, not a filling technique.
Then the closure, against the same answers
Neck finish for fit, liner for contact, temperature rating for what it goes through. A specified bottle with an unconsidered cap is a half-done specification and it is the usual version of this mistake.
Then cleanliness
General purpose or certified pre-cleaned. For trace work that is a different product with documentation, and washing a general bottle yourself is not an equivalent.
Then the label
Enough flat area for a readable identity that survives wet and cold. It sounds trivial next to the chemistry and it is the most common reason a sample is lost.
Write the answers down once per sample type
A short specification per routine sample, kept with the method, means the next order is a lookup rather than a rederivation and the next person orders the same thing you did.
Re-run it when anything changes
A new analyte, a new method version, a new supplier or a new preservative each invalidate part of the answer. The checklist is cheap to repeat and expensive to skip.
The order matters
Starting from the catalog and working back to the method is how people end up justifying the bottle they already have. Starting from the method and arriving at the catalog last means the answer is determined rather than rationalized, which is the entire discipline.
Keep it with the method, not in a drawer
The checklist is only useful at the moment somebody is about to order, so it belongs where the method lives. Filed separately it becomes a document that was written once and never consulted.
If any answer is unknown, that is the thing to resolve rather than the order to place. An unknown here becomes a wrong number later, and the number is the product.