“Analyte” is frequently used as synonym for “measurand”: is that correct?

Abstract

In a measurement, a most basic concept is ‘‘measurand.’’When starting to draft a plan for a process called mea-surement, we must clearly specify the goal of the process.That goal must have been discussed with the end user(frequently called the customer) on beforehand. Agreeingon such a goal and respecting this agreement will ensurethat the result obtained at the end of the process as carriedout by the analyst, is fit for the intended use [1] of the resultby the end user. The product of a discussion between theend user of the result and the analyst is about what is thegoal of the process. Thereby the end user should not have toworry about how the analyst performs the process: that iswhat the end user pays the analyst for. Thus, the analystmust make sure that the measurement result (s)he obtains atthe end of the process is clearly related to the goal (s)he hasagreed with the end user. All intermediate steps that need tobe taken during the process, including whatever chemicaloperations such as weighings, dissolutions, separations,chemical transformations, preparation of samples suitablefor introduction into whatever type of spectrometer, mea-surements of other input quantities (see entry 2.50 in [2])into the measurement function (see entry 2.49 in [2]), etc.,deemed necessary by the analyst to reach the goal agreedwith the end user, ultimately are the analyst’s choice anddecision, not the end user’s. The analyst is in control ofassigning the value (with associated measurement uncer-tainty) to the measurement result [3]. The intermediatesteps, important as they may—or because sometimes theyare so important—pertain to the answer to the question howthe goal agreed with the end user, is attained by the analyst.This logic is the rationale for the fundamental change inthe definition of ‘‘measurand’’ in the 3rd edition of theInternational Vocabulary of Metrology—VIM [2].It is important to note that the ‘‘quantity subject tomeasurement,’’ the former definition of ‘‘measurand’’ inthe VIM, 2nd edition [4], was very different from the newdefinition in the 3rd edition of the VIM: ‘‘quantity intendedto be measured.’’ The definition in the 3rd edition is ofgreat help in chemistry, as chemistry-specific intermediatesteps now become part of the process of measurement,possibly including measurements performed on interme-diate chemical species showing up in the process (inclinical chemistry, such species is called component orchemical substance [6] and its meaning is considered to beoverlapping with the meaning of the term analyte). Thathas the consequence that all chemical preparation work ona sample in view of obtaining a measured value (withassociated uncertainty) for the intended measurement resultof an a priori specified quantity (the measurand) in theoriginal material as well as any desired transformation of achemical species and measurements of its properties,become an inherent part of the planned process. That alsohas the consequence that the uncertainty naturally associ-ated with each step in that chemical preparation work aswell as with any transformation process will have to beincluded in the uncertainty budget (see entry 2.33 in [2]) ofthe final measurement result for the measurand. That willincrease this final uncertainty, making it larger than just,for example, the measurement of electric current(s) in aninstrumental measuring system (see entry 3.2 in [2]). Butsuch a measurement uncertainty will correspond to a morerealistic measure of ‘‘doubt’’ [5] about the measurement