美国的分析标准
Analytical Standards
Introduction
Standards are materials containing a known concentration of an analyte. They provide a reference to determine unknown concentrations or to calibrate analytical instruments.
The accuracy of an analytical measurement is how close a result comes to the true value. Determining the accuracy of a measurement usually requires calibration of the analytical method with a known standard. This is often done with standards of several concentrations to make a calibration or working curve.
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Primary Standards
A primary standard is a reagent that is extremely pure, stable, has no waters of hydration, and has a high molecular weight.
Some primary standards for titration of acids:
sodium carbonate: Na2CO3, mol wt. = 105.99 g/mol
tris-(hydroxymethyl)aminomethane (TRIS or THAM): (CH2OH)3CNH2, mol wt. = 121.14 g/mol
Some primary standards for titration of bases:
potassium hydrogen phthalate (KHP): KHC8H4O4, mol wt. = 204.23 g/mol
potassium hydrogen iodate: KH(IO3)2, mol wt. = 389.92 g/mol
Some primary standards for redox titrations:
potassium dichromate: K2Cr2O7, mol wt. = 294.19 g/mol
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Secondary Standards
A secondary standard is a standard that is prepared in the laboratory for a specific analysis. It is usually standardized against a primary standard.
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NIST Standard Reference Materials
The National Institute of Standards and Technology (NIST) provide a wide variety of standard reference materials (SRMs) for validating and calibrating analytical methods. Some examples of SRMs:
for chemical composition
elements in iron, steels, and other metal alloys
sulfur in fossil fuels
polychlorinated biphenyls (PCBs) in oils
elements in foods and beverages (e.g. milk powder, wheat flour)
for physical properties
strength and melt fow of polyethylene pipe
radioactivity
electrical resistivity of Si
for engineering materials
particle sizes
magnetic computer storage media
surface flammability