PREPARATION OF IN-HOUSE REFERENCE MATERIAL FOR THE DETERMINATION OF SELECTED HEAVY METALS IN SOILS OF MINNA, NIGER STATE

Abstract

Method performance in analytical chemistry is checked using certified reference materials (CRMs). Due to their high production cost, CRMs cannot be used routinely in daily laboratory work; therefore, in-house reference materials are preferred. An in-house soil reference material was prepared in this project for use as quality control material in the determination of Fe, Zn, Cu, Pb, Mn, Cr and Cd in soil. The FUTMX7316SRM was prepared by mixing soils of road sides, mechanic workshops, dump sites and agricultural farms from different parts of Minna metropolis. The homogeneity of the bulk sample was checked before and after the soil was bottled using total nitrogen and organic carbon as homogeneity indicators. The texture of the bulked soil was also determined. Ten systematically selected samples were digested in triplicate using one of the commonly used method amongst Nigerian students and researchers, hotplate aqua regia, and the digest analyzed in four different laboratories in Nigeria for the concentrations of Fe, Zn, Cu, Pb, Mn, Cr and Cd. Certified Reference Material (CRM-989), prepared by International Soil-Analytical Exchange, Wageningen University of Environmental Sciences, Netherlands, was also analyzed for quality control and traceability of the prepared FUTMX7316SRM. The result obtained were summarized using mean, median, standard deviation and percent coefficient of variance. Analysis of variance was carried out with the results. No statistically significant differences were observed for within- or between-bottle results. Therefore, the material prepared is considered homogeneous fit for use as quality control material in the determination of Fe, Zn, Cu, Pb, Mn, Cr and Cd in soil. The property value revealed that the prepared reference material contained 0.41 ± 0.02 % total organic carbon, 0.16 ± 0.04 % total nitrogen, 236.21 ± 41.78 mg/kg Zn, 213.25 ± 108.63 mg/kg Mn, 17.46 ± 3.50 mg/kg Pb, 18.38 ± 7.55 mg/kg Cu, 1.35 ± 1.56 mg/kg Cd, 9071.64 ± 368.92 mg/kg Fe and 127.65 ± 39.95 mg/kg Cr. The values are traceable to the Certified Reference Material (CRM-989) used, and can therefore be used for inter-laboratory campaign and other quality control purposes.