Box 0-1 Constructing a Representative Sample

Al3+ can be masked by treating the sample with excess F to form AIFJ. which does not react with EDTA. 

Sample preparation is the process of converting a representative sample into a form suitable for chemical analysis, which usually means dissolving the sample. Samples with a low concentration of analyte may need to be concentrated prior to analysis. It may be necessary to remove or mask species that interfere with the chemical analysis. For a chocolate bar. sample preparation consisted of removing fat and dissolving the desired analytes. 

The reason for removing fat was that it would interfere with chromatography. 

Measure the concentration of analyte in several identical aliquots (portions). The purpose of replicate measurements (repeated measurements) is to assess the variability (uncertainty) in the analysis and to guard against a gross error in the analysis of a single aliquot. The uncertainty of a measurement is as important as the measurement itself, because it tells us how reliable the measurement is. If necessary, use different analytical methods on similar samples to make sure that all methods give the same result and that the choice of analytical method is not biasing the result. You may also wish to construct and analyze several different bulk samples to see what variations arise from your sampling procedure. 

Deliver a clearly written, complete report of your results, highlighting any limitations that you attach to them. Your report might be written to be read only by a specialist (such as your instructor) or it might be written for a general audience (perhaps your mother). Be sure the report is appropriate for its intended audience. 

Sampling is the process of selecting a representative bulk sample from the lot. Sample preparation converts a bulk sample into a homogeneous laboratory sample. Sample preparation also refers to steps that eliminate interfering species or that concentrate the analyte. 

In a random heterogeneous material, differences in composition are random and on a fine scale. When you collect a portion of the material for analysis, you obtain some of each of the different compositions. To construct a representative sample from a heterogeneous material, you can first visually divide the material into many small regions. For example, if you want to measure the magnesium content of the grass in the 10-meter X 20-meter field in panel a, you could divide 

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