Development of a Certified Reference Material (NMIJ CRM 7202-c) for Trace Elemental Analysis of River Water

A river-water certified reference material (CRM), NMIJ CRM 7202-c was developed by National Metrology Institute of Japan (NMIJ). This CRM is intended for use in the quality control of analyses and the validation of analytical methods and instruments used for analyses of trace elements in river water. To avoid elemental contamination, laboratory wares, such as polypropylene bottles and pipette tip, and polyethylene bottles into which the CRM are filled were immersed in 3 mol L-1 nitric acid for more than 1 week. At least three independent analytical methods were applied to characterize the certified value of each element. Twentyone elements (i.e., Al, As, B, Ba, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Mo, Ni, Na, Pb, Rb, Sb, Se, Sr, Zn) were certified. The certified value for each element was given as the property value +/- expanded uncertainty, with a coverage factor of 2 for the expanded uncertainty. The expanded uncertainties were estimated while considering the contribution of the analytical methods, the method-to-method variance, the sample homogeneity, and the concentrations of the standard solutions for calibration.