Methodology for the Preparation and Study of Multicomponent Certified Reference Materials for Soils Contaminated with Heavy Metals

Abstract

A procedure was developed for preparing certified reference materials (CRMs) for the composition of the matrix of natural soils containing mobile heavy metals in concentrations exceeding their background levels. The procedure for preparing soil CRMs includes sampling soil under natural conditions, drying, grinding and sieving it, mixing it thoroughly for homogenisation, preparing a water solution with pre-set concentrations of heavy metal salts, mixing the soil with a solution of heavy metal salts, and evaporating water at 105 °C. The metrological characteristics of CRMs—homogeneity and stability over time—were determined, and factors affecting the homogeneity of CRMs were revealed: the soil type and texture, the nature of the pollutant, and the pH of the metal solution. An estimate was made of how the heterogeneous distribution of different elements contributed to the error in the CRM values. The contents of copper, zinc, lead, cadmium, nickel, cobalt, and mercury in CRMs were certified in an intra-laboratory study with the participation of 57 accredited Russian laboratories.