We conclude from these results that the ASTM method reliably predicted the actual MDC (scanned) of the Fluorolog® system, and that the Fluorolog® is a spectrofluorometer capable of measuring some of theweakest possible fluorescence from nearly any sample. We also find that the FluoroMax is a highly sensitive instrument, capable of detecting fluorescein nearly as well as the Fluorolog, and can measure fluorescent microsphere dilutions of up to 100 million, corresponding to concentrations as low as 2.3×104 particles mL-1.