An analytical procedure was developed using capillary electrophoresis (CE) coupled on-line to a double-focusing sector field inductively coupled plasma mass spectrometer (DF-ICP-MS) for the analysis of mixtures of lanthanide elements in aqueous samples with natural isotope abundances and in a sample taken from an irradiated tantalum target containing artificial nuclide abundances. A MicroMist AR30-1-F02 nebulizer with a Cinnabar small volume cyclonic spray chamber was used for ICP-MS sample introduction. The CE-ICP-MS interface featured a self-aspirating electrolyte make-up solution for electrical ground connection and control of nebulizer suction. The CE-ICP-MS method features fast run times and small sample sizes (≈35 nL injection volume). Detection limits for the most abundant lanthanide isotopes were 0.72 ppb to 3.9 ppb, an improvement of as much as one order of magnitude compared to a quadrupole ICP-MS system using a similar experimental arrangement. Abundances of the most abundant isotopes of lanthanides were found to be within 0.1–2% of table values for natural samples while isotopes present in smaller amounts were within 3–5% of table values. The method was applied to samples taken from a tantalum material which was exposed to a high energy proton beam for the production of neutrons via spallation reactions. A large fraction of the spallation products were lanthanides containing nuclide abundances unlike natural samples. Thus, a chemical separation step prior to ICP-MS detection was required to avoid isobaric interferences for the accurate determination of nuclide abundances in such samples. The results of the nuclide abundance determinations were compared to theoretical calculations.