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A standard solution created from a secondary standard cannot have its concentration accurately known without stoichiometric analysis against a primary standard. 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 ...
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.
The next quality standard in the hierarchy is known as a secondary standard. Secondary standards are calibrated with reference to a primary standard. [2] The third level of standard, a standard which is periodically calibrated against a secondary standard, is known as a working standard. [2] Working standards are used for the calibration of ...
A burette and Erlenmeyer flask (conical flask) being used for an acid–base titration.. Titration (also known as titrimetry [1] and volumetric analysis) is a common laboratory method of quantitative chemical analysis to determine the concentration of an identified analyte (a substance to be analyzed).
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 .
Sometimes an internal standard is added at a known concentration directly to an analytical sample to aid in quantitation. The amount of analyte present is then determined relative to the internal standard as a calibrant. An ideal internal standard is an isotopically enriched analyte which gives rise to the method of isotope dilution.
The hierarchy preserves the quality of the higher standards. [20] An example of a standard would be gauge blocks for length. A gauge block is a block of metal or ceramic with two opposing faces ground precisely flat and parallel, a precise distance apart. [31] The length of the path of light in vacuum during a time interval of 1/299,792,458 of ...
The EPA reviewed this NAAQS in 1985 and 1996, and in both cases concluded that the existing standard was sufficient. The most recent review by the EPA occurred in 2010, resulting in a new 1-hour NO 2 primary standard set at 100 ppb; the annual average of 0.053 ppm remained the same. Also considered was a new 1-hour secondary standard of 100 ppb.