Field detection and quantification of f-elements is an important problem in radioanalytical chemistry requiring small, portable devices. Here, characterization of a 10 μm Hg film carbon fiber disk microelectrode to accumulate f-elements is described. Accumulation was performed by cathodic deposition and evaluated by anodic stripping and subsequent ICPMS analyses. La(3+) was used as the model element, and subsequent studies were conducted on a 17 element mixture (Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Th). In the model studies, La(3+) undergoes a sorption phenomenon, and as in other studies and confirmed by ICPMS, a monolayer of atoms on the electrode surface is formed. Dissolved O(2) was found to have no effect on the cathodic accumulation of La(3+). Consideration of electrode reaction conditions is made, and reactions are hypothesized. The limit of detection (LOD) was found to be 10(-7) M with mass detection of 10(9) atoms, approximately 5 orders of magnitude less than at conventionally sized electrodes. To solve a dilution problem in follow-on analyses, a suggestion to use microelectrode chip-based sensors was made.