Holding times

Headspace, fill and the closure

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Where the table names a top Because the measurement is about air Volatiles are the same problem Which conflicts with freezing The liner is in contact with the sample Which is why phenolic caps appear in this craft Threads have to survive grit Wide mouth for solids, narrow for water Label before you fill And record the time of collection References

"G, Bottle and top." The table names the closure as part of the container.

Where the table names a top

Dissolved oxygen, by probe and by the Winkler method, is specified as "G, Bottle and top". The closure is not an accessory, it is in the specification.

Because the measurement is about air

A dissolved oxygen sample has to be filled without trapping a bubble and closed without admitting one. A container that cannot be filled that way cannot hold the sample.

Volatiles are the same problem

Anything that will leave the water into a headspace is measured low if there is a headspace to leave into. Fill to overflowing and cap under the surface is the field technique.

Which conflicts with freezing

A full container with no headspace will break if it freezes, so a sample held cold has to be kept cold and not frozen. That is a cooler decision.

The liner is in contact with the sample

11 liners and sealing discs on this shelf. For an organic parameter the liner is a polymer surface touching the water, with the same adsorption question as the bottle wall.

Which is why phenolic caps appear in this craft

14 of them here. The traditional closure where a liner has to resist something, and a small set doing a specific job.

Threads have to survive grit

A soil or sediment sample puts particles on the thread. A cap that will not seat is a sample that leaks in a cooler and a chain of custody with a question in it.

Wide mouth for solids, narrow for water

194 jars and 163 bottles. The split on this shelf happens to match the split in the craft, which is not always true.

Label before you fill

A wet container will not take a marker and a gloved hand will not write neatly. Labelling at the bench before leaving is the practice that survives a cold morning.

And record the time of collection

Because every holding time in the table counts from it. A sample without a collection time has no holding time, which means it has no result.

References

40 CFR 136.3, Table II, selected rows. Oil and grease: G, cool to 6 degrees C or below and acidify to pH below 2, 28 days. Phenols: G, 28 days. Phosphorus (elemental): G, 48 hours. Fluoride: P, no preservation required, 28 days. Silica: P or Quartz, 28 days. Boron: P, FP, or Quartz, nitric acid to pH below 2, 6 months. Cryptosporidium and Giardia: LDPE with field filtration, 1 to 10 degrees C, 96 hours. Dissolved oxygen by probe: G, bottle and top, analyze within 15 minutes. Chlorine, total residual: P, G, analyze within 15 minutes. pH: P, FP, G, analyze within 15 minutes. Coliform and E. coli: PA, G, 8 hours. Hardness: P, FP, G, 6 months. Nitrate: P, FP, G, 48 hours. ecfr.gov

The Davis Pack Supply catalog, measured 19 October 2026. The field sampling shelf is 768 rows: 359 containers and 409 closures. 5 mL to 950 mL with a median of 118; 124 containers at 60 mL or under, 211 at 120 or under, 317 at 500 or under, and nothing above a litre. 146 PET, 108 glass, 92 HDPE, 13 PP, no LDPE and no fluoropolymer. 194 jars, 163 bottles, 2 tubes. 103 clear, 82 white, 52 amber, 34 natural. Closures: 346 continuous thread, 27 dome lids, 14 phenolic, 11 liners and sealing discs, 6 specialty.

Written from 40 CFR 136.3 Table II and from the catalog as it stood on 19 October 2026. Part 136 governs Clean Water Act compliance monitoring; it is used here for everything else as the best available statement of what a container does to a water sample, not as a rule that binds a student with a creek. Nothing on this shelf is sold precleaned or certified for regulated sampling, and no preservation chemistry is given, because that belongs to the laboratory running the analysis.