IPA: /ˌaɪsəˈtoʊpɪkli/
KK: /ˌaɪsəˈtoʊpɪkli/
In a way that relates to isotopes, which are different forms of the same element with varying numbers of neutrons.
The samples were analyzed isotopically to determine their composition.
Isotopically → It is formed from "iso-" (from Greek "isos", meaning equal) and "topos" (meaning place) combined with the suffix "-ically" (meaning in a manner). The term refers to something that relates to equal places or forms of an element, specifically in the context of isotopes having the same number of protons but different numbers of neutrons.
Think of 'equal' ('iso-') forms of an element in different 'places' ('topos') — that's what isotopically refers to.