Sunday, November 11, 2012

Reagent grade water and reference materials


There are 3 types of water. I through III Type I is reagent grade water.

Distillation, ion exchange, reverse osmosis, and UV oxidation are used to prepare reagent grade water.

Type III water: It is used for glassware washing. It may be used for certain qualitative procedures, such as those used in general urinalysis

Type II water: It is used for general laboratory testing not requiring type I water Storage should be maintained to ensure minimum chemical or bacterial contamination. This is used for normal laboratory practical procedures and laboratory testings.

Type I water: It should be used in test method requiring minimal interference and maximal precision and accuracy. Such process include, trace metal, enzyme, and electrolyte estimation, and preparation of all calibrators and solution for reference materials. 

(Source: Tietz clinical Chemistry, 4th Edition)    

Higher is the amount of ionizable material, lower the resistivity. Water if passes through 0.2µm filter it is considered to be free of particulate matter. If passed through activated carbon it is considered to contain minimum organic material.


Chemicals that meet specifications of American Chemical Society (ACS) are called reagent or analytical grade. These reagents include the actual concentration along with maximum amount or impurities.


Primary reference material: These are highly purified chemicals that are directly weighed or measured to produce a solution whose concentration is exactly known. The IUPAC has proposed a degree of 99.98% purity for primary reference material. These are used for calibration of solution of unknown strength. They are supplied with certificate of analysis. These substances must be sufficiently stable and should not be hygroscopic so that water is not absorbed during weighing.

Secondary reference materials: These are solutions whose concentrations cannot be prepared by weighing the solute and dissolving a known amount into a volume of solution. The concentration of secondary reference material is determined by analysis of an aliquot of solution by a reference method, using primary reference material to calibrate the method.
Certified reference standards (SRMs): These standards have well characterized chemical and physical properties and are issued with certificates that give the results of characterization.

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