In chemistry, coprecipitation (CPT) or co-precipitation is the carrying down by a precipitate of substances normally soluble under the conditions employed.^[1] Analogously, in medicine, coprecipitation is specifically the precipitation of an unbound "antigen along with an antigen-antibody complex".^[2] It has been suggested that the central science be merged into this article or section. ... medicines, see medication and pharmacology. ...

Coprecipitation is an important issue in chemical analysis, where it is often undesirable, but in some cases it can be exploited. In gravimetric analysis, which consists on precipitating the analyte and measuring its mass to determine its concentration or purity, coprecipitation is a problem because undesired impurities often coprecipitate with the analyte, resulting in excess mass. This problem can often be mitigated by "digestion" (waiting for the precipitate to equilibrate and form larger, purer particles) or by redissolving the sample and precipitating it again.^[3] Analytical chemistry is the analysis of material samples to gain an understanding of their chemical composition and structure. ... Gravimetric analysis is a quantitative chemical analysis done by weighing a sample of a purified and dried precipitate. ... An Analyte is the substance or chemical constituent that is undergoing analysis. ...

On the other hand, in the analysis of trace elements, as is often the case in radiochemistry, coprecipitation is often the only way of separating an element. Since the trace element is too dilute (sometimes less than a part per trillion) to precipitate by conventional means, it is typically coprecipitated with a carrier, a substance that has a similar crystalline structure that can incorporate the desired element. An example is the separation of francium from other radioactive elements by coprecipitating it with caesium salts such as caesium perchlorate. Otto Hahn is credited for promoting the use of coprecipitation in radiochemistry. Radiochemistry deals with the use of radioactivity to study ordinary chemical reactions. ... General Name, Symbol, Number francium, Fr, 87 Chemical series alkali metals Group, Period, Block 1, 7, s Appearance metallic Atomic mass (223) g·mol−1 Electron configuration [Rn] 7s1 Electrons per shell 2, 8, 18, 32, 18, 8, 1 Physical properties Phase solid Density (near r. ... General Name, Symbol, Number caesium, Cs, 55 Chemical series alkali metals Group, Period, Block 1, 6, s Appearance silvery gold Atomic mass 132. ... Caesium perchlorate, CsClO4, is a perchlorate of caesium. ... Otto Hahn and Lise Meitner, 1913, at the KWI for Chemistry in Berlin Otto Hahn (March 8, 1879 – July 28, 1968) was a German chemist and received the 1944 Nobel Prize in Chemistry. ...

There are three main mechanisms of coprecipitation: inclusion, occlusion, and adsorption.^[3] An inclusion occurs when the impurity occupies a lattice site in the crystal structure of the carrier, resulting in a crystallographic defect; this can happen when the ionic radius and charge of the impurity are similar to those of the carrier. An adsorbate is an impurity that is weakly bound (adsorbed) to the surface of the precipitate. An occlusion occurs when an adsorbed impurity gets physically trapped inside the crystal as it grows. Enargite crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... Crystalline solids have a very regular atomic structure: that is, the local positions of atoms with respect to each other are repeated at the atomic scale. ... Ionic radius is a concept for expressing the sizes of ions in ionic crystals. ... In chemistry, a molecule is adsorbed onto a surface when temporary bonds are formed between the surface and the molecule. ...

Besides its applications in chemical analysis and in radiochemistry, coprecipitation is also "potentially important to many environmental issues closely related to water resources, including acid mine drainage, radionuclide migration in fouled waste repositories, metal contaminant transport at industrial and defense sites, metal concentrations in aquatic systems, and wastewater treatment technology"^[4]

References

1. ^ Patnaik, P. Dean's Analytical Chemistry Handbook, 2nd ed. McGraw-Hill, 2004.
2. ^ http://cancerweb.ncl.ac.uk/cgi-bin/omd?coprecipitation. Accessed 5/9/07.
3. ^ ^{a b} Harvey, D. Modern Analytical Chemistry. McGraw-Hill, 2000.
4. ^ http://www.cosis.net/abstracts/EAE03/06552/EAE03-J-06552-1.pdf . Accessed May 10, 2007.