In terms of certification of "DNase-free" consumables, I would like to understand the DNase testing methods better. Generally, nuclease-free water is run through plastic ware (pipette tips, microtiter plates, eppendorfs, etc), then incubated with a DNA ladder and appropriate buffer at 37°C, before analysing the product by agarose gel electrophoresis. Most manufacturers (if stated at all), say that the pass criteria is that samples must look exactly the same as the DNA negative control (e.g. no smearing, well defined ladder). Does anyone know, is this done by expert eye (highly subjective), or do you actually measure the fluorescent output from the agarose gel? If you measure the fluorescent output, how do you do this and what are the measurement tolerances? It is often stated that the test sensitivity is 10^-7 Kunitz Units/µL – what does this actually mean and how is it determined? I know the definition of a Kunitz unit, but am unsure how it is applied in this case. TIA