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 ¼ 0.01 be used. The homogenized sample was distributed to participants in an intercomparison exercise to validate the results of the laboratory preparation.

Modern Extraction Techniques

“…Nyiredy (3) discussed the necessity of extraction methods to characterize both the volatile and nonvolatile components of these natural products. Similarly, the preparation of internal reference standards of soil and plant samples was proposed (4). Statistical methods to ensure sample homogeneity were investigated, and an interlaboratory validation was performed.…”

Extraction of phenolic compounds from Temnocalyx obovatus

“…Nitrogen was selected as the primary indicator of homogeneity because of its relative ease of determination by the Kjeldahl method. To determine the degree of homogeneity, the mean variance of the nitrogen analysis was calculated and a matrix of coefficients was set-up (Lo'pez-Romero et al, 2005) and the results are shown in Table 1.…”

“…The residue was discarded. Homogenization of the material was carried out by mixing the entire quantity of powder having particle size smaller than 250 µm in a plastic container for 60 h. Sub-samples, N1 to N10 were selected from the bulky sample by random sampling (Lo'pez-Romero et al, 2005). To test sample homogeneity with respect to nitrogen, a mass of 0.5 g of powdered leaves was randomly selected from each sub-sample into a digestion flask followed by determination of total nitrogen by the the Kjeldahl method which was adopted (Willis et al, 1996).…”

“…It can be stated that for quality of analytical data to be realized, it is essential that a control sample is homogeneous so that sub-samples used in the batches are identical. A simple homogenization of a plant sample without subjecting it to strict statistical test is not a guarantee of homogeneity for all such analytical parameters (Lo'pez-Romero et al, 2005). In Zimbabwe, despite the widespread use of wild plants as medicines, documented literature on antioxidant composition of plant extracts is still very limited and there exist a multitude of unexplored species.…”