Quality Assurance/Quality Control
CE calibration standards were prepared by dissolving pre-weighed amounts of K2CrO4 in
DDW. To assure accurate CrVI measurements, the CE CrVI calibration solutions were
standardized by measuring total dissolved chromium (CrT) by using Flame-AAS. Figure S4
shows a) the calibration curve for the CrVI AAS standards (absorbance versus CrT) and b) a
comparison of the measured and nominal CrVI concentrations of the CE standards. The excellent
agreement between measured and nominal CrVI concentrations confirms that the concentration of
CrVI in the CE standards are accurate.