Efficient Calculation of Fine Structure Isotope Patterns via Fourier Transforms of Simplex-Based Elemental Models R package ecipex version 1.1.1 Provides a function that quickly computes the fine structure isotope patterns of a set of chemical formulas to a given degree of accuracy (up to the limit set by errors in floating point arithmetic). A data-set comprising the masses and isotopic abundances of individual elements is also provided and calculation of isotopic gross structures is also supported. Software Imports: CHNOSZ Andreas Ipsen <andreas.b.ipsen@gmail.com> Comprehensive R Archive Network (CRAN) Andreas Ipsen [aut, cre] (ORCID: <https://orcid.org/0000-0002-2566-8811>) GPL (>= 2) 2025-04-21 application/tgz https://CRAN.R-project.org/package=ecipex doi:10.32614/CRAN.package.ecipex