Precision mass measurement using two ions in a Penning trap

We have implemented a technique for precision mass comparison of two ions simultaneously trapped in a Penning trap in which each ion is alternately positioned at the center of the trap -- where its cyclotron frequency is measured -- or else parked in a large cyclotron orbit. Using the method to compare $^{28}$SiH$_{3}^{+}$/$^{31}$P$^{+}$ we have obtained a new atomic mass for $^{31}$P of 30.973 761 999 7(61) u. We have also used the method to observe shifts in the cyclotron frequency of the molecular ions CO$^{+}$ and PH$^{+}$ due to the interaction between the ion's polarizability and the motional electric field. Progress towards a) implementing \textit{simultaneous} cyclotron frequency comparisons using two ions in a coupled magnetron orbit, b) a precision measurement of the mass difference between $^{3}$T and $^{3}$He, c) the use of polarizability shifts for single ion molecular spectroscopy, and d) a precision mass measurement of $^{40}$Ca will also be reported.