The use of ultra-low-energy probes for the characterization of shallow implants using secondary ion mass spectrometry is now widely employed. However, as the energy is reduced, both the sputter and ion yields fall, leading to long analysis times and decreased sensitivity. This effect is most apparent when analyzing diffused low-energy implants where both dosimetry and junction depth are to be determined. To obtain accurate dosimetry of a distribution with a very narrow but high surface concentration, probes of 100-200 eV must be used (O-2(+) for analysis of B in Si). However, over most of the depth of the analysis, extreme depth resolution is not required. This work demonstrates the use of matching the ion energy to the task in hand, and investigates the quantification issues of changing energy within a single depth profile.