Measurement of an analytical signal or measurement of the content of an analyte?

Abstract

The paper raises the question about the place of measurement in chemical analysis: whether a measurement is concentrated, as often believed, at the step of analysis where an analytical signal is produced or quantitative analysis as a whole is an indirect measurement of the content of an analyte. Detailed background information on the subject is presented with some examples from well-known textbooks on analytical chemistry, in which the step of “measurement” of an analytical process is treated as a measurement of the analyte (content). Such understanding agrees with the relevant metrological concepts presented in the IUPAC Compendium of Analytical Nomenclature. A characteristic feature of any measurement is a comparison with a unit of quantity to be measured. This is done at the final step of analysis, when the analytical signal obtained for a given analyte is compared with a signal corresponding to the unit of analyte content. The determination of the analytical signals in units of a corresponding physical quantity is often unnecessary in chemical analysis. For this and other reasons one can speak about the measurement of a signal only with a certain degree of conventionality.