XRF Precision

LOD = limit of determination in this table. We determined these 2 sigma limits by analyzing about 250 repeat experiments over the course of 14 months. These therefore represent our working day-in, day-out precision. Clearly if your concentration is less than our LOD your result is highly uncertain. In contrast to many other labs, we report results down to zero because there is information at 1 and 2 sigma even though most limits of detection are defined at three sigma. You can be 95% confident in our result at say 2 +/- 2 ppm, but strict detection limit usage would preclude reporting the number at all because you don’t have 99% confidence you have “detected” something. We are satisfied with the lesser confidence interval but you can choose your own usage.

LOD Table (pdf)