Flow cytometric detection of specific rare-event targets within high-background samples such as water or food are frequently defeated by the extremely large population of non-target background particles. Time-gated detection of long lifetime fluorescence (>10μs) labeled microbial targets has been proven highly efficient in suppressing this non-target autofluorescent (<0.1μs) background. A time-gated luminescence (TGL) flow cytometer using UV LED excitation has demonstrated the successful detection of rare-event particles in high autofluorescence background samples. In this report, high-quality 5μm europium beads were made (homogenous intensity and aggregation free) for a detailed evaluation of the prototype performance. The known number of beads (10±2, 100±20 and 1000±100) were first sorted by a conventional flow cytometry sorter, and spiked into an environmental water concentrate (1 ml; containing >10 million non-target particles). The recovery rate for counting these very-rare-event particles using the TGL flow cytometer was then found to be 100%±20% between bead concentrations evaluated.