This paper describes a device that seals samples of seawater in situ in an aluminum or copper tube in millimeter quantities such that the dissolved gases are retained and can be transferred to vacuum systems without either the loss of the contained gases or the introduction of air. The instrument has been tested to depths of 4000 m in the open ocean under modestly harsh conditions.
Bieri, Rudolf H.. 1965. "Hermetically-sealing seawater sampler." Journal of Marine Research 23, (1). https://elischolar.library.yale.edu/journal_of_marine_research/1040