Production and characterization of a candidate soil reference material for inorganic chemical analysis

Abstract

The development of reference materials is essential to ensure the quality and comparability of analytical results. This dissertation presents the study of a candidate soil reference material for inorganic analysis, collected from an area impacted by lead metallurgical activities in Santo Amaro da Purificação, Bahia, Brazil. The soil underwent preparation procedures, including drying, sieving, homogenization, and sterilization by gamma radiation, resulting in 100 vials of 30 g each for the certification process. Homogeneity was assessed through microwave-assisted digestion and multi-element determination (As, Ca, Cd, Cu, Mg, Mn, Na, Ni, Pb, Sb, Se, Sr, and Zn) using inductively coupled plasma optical emission spectrometry (ICP OES). Minimum sample mass, within-bottle, and between-bottles tests were performed and validated by analysis of variance (ANOVA), according to ISO 35 guidelines, and further confirmed by the chemometric technique Data-Driven Soft Independent Modeling of Class Analogy (DD-SIMCA). Additionally, the innovative use of a multi-element robust Z-score approach was proposed as an alternative tool for homogeneity assessment. Subsequently, an interlaboratory study involving 28 analytical chemistry laboratories from Brazilian higher education institutions was carried out to certify the chemical elements. The results were evaluated using Cochran, Grubbs, Z-score, and robust Z score tests, ensuring the reliability of the assigned values. The certified elements were As, Cd, Ca, Cu, Mg, Mn, Ni, Pb, and Zn, with uncertainty estimates considering homogeneity, stability, and interlaboratory studies. The findings confirm that the developed material exhibits suitable properties to be used as a reference material, contributing to the improvement of metrological reliability in soil analysis.