  The use of highly charged ions increases the precision and resolving power,
in particular for short-lived species produced at on-line radio-isotope beam
facilities, achievable with Penning trap mass spectrometers. This increase in
resolving power provides a new and unique access to resolving low-lying
long-lived ($T_{1/2} > 50$ ms) nuclear isomers. Recently, the $111.19(22)$ keV
(determined from $\gamma$-ray spectroscopy) isomeric state in $^{78}$Rb has
been resolved from the ground state, in a charge state of $q=8+$ with the TITAN
Penning trap at the TRIUMF-ISAC facility. The excitation energy of the isomer
was measured to be $108.7(6.4)$ keV above the ground state. The extracted
masses for both the ground and isomeric states, and their difference, agree
with the AME2003 and Nuclear Data Sheet values. This proof of principle
measurement demonstrates the feasibility of using Penning trap mass
spectrometers coupled to charge breeders to study nuclear isomers and opens a
new route for isomer searches.
