Before analysis of sample extracts, we calibrated the system with a mix of the four mercury species from approximately 100 ng/L (ppt) up to 10 µg/L (ppb). Figure 2 shows the linear calibration curves, as well as the background equivalent concentration (BEC) of the mobile phase. For all species, the BEC value was lower than 20 ng/L. These low BEC values demonstrate the small contamination from the mobile phase and the capability of the system to detect low levels of mercury