Recent improvements in isobaric suppression for medium-mass isotopes, e.g. (41)Ca, offer new possibilities for tandem accelerators with terminal voltages of 3 MV or lower; i.e. when dealing with particle energies <= 1 MeV/amu. In particular, detection of (41)Ca requires sufficient discrimination of the stable isobar (41)K. We explored the limits of (41)Ca detection at our 3-MV AMS facility by means of different types of particle detectors: The ATOF method, which is based on the different flight-time of isobars after passing a thick absorber foil. The second method makes use of a new type of compact ionization chamber: (41)K and (41)Ca are separated in energy due to their different energy loss in the detector entrance foil and the detector gas, which is measured via a segmented anode. At VERA we measured (41)Ca/Ca ratios below 10(-13) for commercial CaF(2) material serving as blank samples. CaH(2) sputter targets, with the extraction of CaH(3)(-) yielded background ratios as low as (41)Ca/Ca = 1 x 10(-15). The typical measurement precision at VERA for (41)Ca measurements was between 2% and 5%. These results demonstrate that AMS facilities based on 3-MV tandems have reached the sensitivity level of larger AMS facilities for a wide range of applications, with the advantage of high overall efficiency and sample throughput. (C) 2009 Elsevier B.V. All rights reserved.