Combustion Capsule Formation for Stable Isotope or Total Element Analysis

Last revised July 22, 1997

Combustion capsule formation

Sample droppers are mechanical devices and subject to jamming on poorly formed sample capsules. The forming device shown below does a very good job of compressing sample material in tin capsules into neat little cylinders (like the one in the lower right in the illustration) that will not jam. Vendors of supplies for elemental analyzers will happily sell you (for an astonishing price) one of these devices machined from stainless steel -- note however that a perfectly functional workalike can be improvised from a block of plastic, a nail, a drill and a little ingenuity.

N.B. a sample tin mushed up into a ball with nothing but tweezers will jam!

(IMAGE: Capsule formation, tweezer1.gif)

When a large number of such sample capsules are needed, the question of how to manage and identify them arises. One tiny encapsulated sample tends to look much like another. A convenient solution is to store one capsule in each well of a 96-well plastic cell-culture (or microtiter, or eliza) plate, which is manufactured with the rows labelled A-H and the columns numbered 1-12, and keep a separate key stating that well A1 contains sample 1, A2 contains sample 2 and so on. These plates are costly when new because they are sterile. For managing tins, however, clean used plates are quite acceptable.

(IMAGE: Microtiter plate, wells02.gif)

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