How to Prepare a Good Plant Sample for Internal Reference Material

Abstract

To evaluate their daily work in analytical measurements, all soil analysis laboratories must have their own low‐cost reference material to substitute high‐cost certified reference materials. This standard can be used to substitute routine use of high‐cost certified reference material (CRM). This standard can be used to substitute routine use of CRM or conventionalized reference materials in case the former are not available. This article presents a simple procedure for preparing a standard for plant material that has high quality and homogeneity for internal use in laboratories. This procedure can also be used to prepare homogeneous soil samples. As a preliminary analytical indicator of homogeneity, water‐soluble potassium and total zinc contents were used. The Levene test was selected as the statistical test of homogeneity of the material. The process is iterative and concludes when the value of F of the results obtained from the analysis of variance of the residuals is less than the critical value of F for a given selected probability. It is recommended that a p=0.01 be used. The homogenized sample was distributed to participants in an intercomparison exercise to validate the results of the laboratory preparation.