If one wants to stick to purely statistical parlance, then it is perfectly acceptable to refer to single element of a sample as un individu, even if it is of inanimate nature. Another possibility is unité statistique (see here and here.)
However, it is necessary to keep in mind that sample / échantillon has ambiguous meaning both in English and French:
- From statistical viewpoint it is a collection of items/individuals sampled from a population
- In specific fields (like physics, biology, medicine, etc.) it often means a single item / device that is an object of study: rock sample, urine sample, etc. If analyzed statistically, many such samples form what a statistician would call a sample from population.
As a more specific example, I could attest the use in computational biology, where the data taken from a single person are referred to as échantillon, and statistical analysis is performed on an ensemble/collection des échantillons (see also statistical ensemble.)
Thus, referring to a single item as échantillon and the collection as ensemble des échantillons is understandable in most fields - perhaps better than the proper statistical use of terms.