A method for the determination of bismuth in high purity ammonium paratungstate by coprecipitation-hydride generation-atomic fluorescence spectrometry has been proposed. Coprecipitation of bismuth with lanthanum hydroxide was to be separated and concentrated. It was found that the bismuth could be recovered after two times of coprecipitation. The optimum experimental parameters,and the effect of coexistent elements on the determination of bismuth were investigated. The detection limit and determination limit of Bi were 0.020ng/mL and 0.012 μg/g respectively. The recoveries were 92.8%～108.4% and the RSD was 4.6%.The method can be applied to analyzing the trace bismuth in high purity ammonium paratungstate.

 

In chemistry, coprecipitation (CPT) or co-precipitation is the carrying down by a precipitate of substances normally soluble under the conditions employed. Analogously, in medicine, coprecipitation is specifically the precipitation of an unbound "antigen along with an antigen-antibody complex".

 

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.

 

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.