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A primary standard in metrology is a standard that is sufficiently accurate such that it is not calibrated by or subordinate to other standards. Primary standards are defined via other quantities like length, mass and time. Primary standards are used to calibrate other standards referred to as working standards. [1] [2] See Hierarchy of Standards.
An example of a secondary standard is sodium hydroxide, a hydroscopic compound that is highly reactive with its surroundings. The concentration of a standard solution made with sodium hydroxide may fluctuate overtime due to the instability of the compound, requiring for calibration using a primary standard before use.
An example is the determination of free fatty acid content. Saponification value: the mass in milligrams of KOH required to saponify a fatty acid in one gram of sample. Saponification is used to determine average chain length of fatty acids in fat. Ester value (or ester index): a calculated index. Ester value = Saponification value – Acid value.
The international prototype of the kilogram (IPK) is an artefact or prototype that was defined to have a mass of exactly one kilogram.. In metrology (the science of measurement), a standard (or etalon) is an object, system, or experiment that bears a defined relationship to a unit of measurement of a physical quantity. [1]
Standards are the fundamental reference for a system of weights and measures by realising, preserving, or reproducing a unit against which measuring devices can be compared. [2] There are three levels of standards in the hierarchy of metrology: primary, secondary, and working standards. [20]
ISO 22000:2018 Food safety management systems – Requirements for any organization in the food chain; ISO/TS 22002 Prerequisite programmes on food safety ISO/TS 22002-1:2009 Part 1: Food manufacturing; ISO/TS 22002-2:2013 Part 2: Catering; ISO/TS 22002-3:2011 Part 3: Farming; ISO/TS 22002-4:2013 Part 4: Food packaging manufacturing
Secondary reference standards: Reference standards calibrated against and traceable to primary WHO materials and intended for use in routine tests; Reference reagent: a WHO reference standard, the activity of which is defined by WHO in terms of a unit; For chemical substances some pharmacopoeias [10] use the WHO terms [11]
These standards are conventionally accepted as best practice and used globally by industry and organizations. In circumstances and situations there are certain methods and systems that are used as benchmarks, guidelines or protocols for communication , measurement , orientation , reference for information , science , symbols and time .