This is part 4 of my epic discussion on shipping environmental samples (see here and here and here for previous installments).
Environmental samples are much like samples gathered as part of a criminal investigation: you need to prove that they were collected properly (that is, that they are representative of actual conditions) and that they have not been tampered with.
The chain of custody involves two parts: keeping samples secure, and documenting the handover of samples.
Most work plans will specify that samples will be kept under the control of the sampler (or someone) until shipment. Practically speaking, this means that coolers should be kept at a staging area, or the trailer, or in your vehicle. They should not be shoved under the trailer or tucked behind a storage shed overnight because they'll stay cool and not-underfoot that way.
The magic token we use to document sample security is a custody seal - a sticker that you sign and date, and then cover either side of the cooler with (or every individual sample, depending on the jurisdiction). Then you usually cover the custody seal and cooler with a few wraps of tape. The idea is that if someone cuts into the cooler/opens the sample jar, they will damage the seal.
The custody seal may be provided by the lab or the sampling firm. In a pinch, I've scribbled my signature and date on a piece of paper and taped that to the cooler. Alternately, you may have a restricted/special supply so that you can document exactly which seal is associated with which cooler/sample.The more specific/detailed the custody seal procedure is, the longer the whole process takes and the more likely you are to screw up, prompting howls of outrage from the lab, the lead chemist, the regulatory agency, etc.
Documenting sample handover
We all use a form called a chain of custody (COC), which is either provided by the lab, or the sampling organization, or the sampling organization's client. That form lists the sample ID, bottleware (how many containers? What type?), preservative, date/time collected, and analyses to be performed. It may list laboratory quality control (QC) samples for the lab. It should also include a note if the samples are screaming hot/pure product or may otherwise require special handling. The form also includes a place for the sampler to sign and for the person handling the samples/packing the cooler to sign and date with the time. When the sample is handed over to the lab/courier or the lab opens the cooler, that person signs. Any time the samples change hands, the COC is signed or a new one is produced. Eventually, a copy of the completed COC is provided with the lab data to show how the samples were handled.
Ideally, you have one COC per shipment. But sometimes you have multiple coolers and need separate COCs. Good luck squashing in that one bottle at the end!
The COC is checked by the lab and by the sampling firm and/or client lead chemist to make sure everything was done correctly. If not, the data may be qualified or rejected, and may require re-sampling. Regulators and consultants for the opposition (if in a legal dispute) scrutinize this stuff.
This chain of custody process can be frustrating to a scientist, because it has zero impact on the analytical results. But ultimately, the samples are part of a legal process that is just as important to the overall project.