Rapid coprecipitation technique for the separation and preconcentration of trace elements

Coprecipitation is one of the most useful methods for the separation and preconcentration of trace elements. In this method, a carrier element is precipitated by using an appropriate precipitant in a solution, and trace elements in this solution are coprecipitated along with the precipitate (so-called coprecipitant). The precipitate has to be completely collected; however, the operation is tedious and time-consuming. To overcome this weak point, a rapid coprecipitation technique, which does not require the quantitative recovery of the precipitate, has been developed. In this technique, any trace elements coprecipitated can be determined based on internal standardization using carrier element as an internal-standard element, because loss of the precipitate can be estimated by the difference in the amount of the carrier element before and after coprecipitation. The carrier element used for this technique has to satisfy the following requirements: 1) negligible content of the carrier element in samples, 2) quantitative precipitation of the carrier element, 3) quantitative coprecipitation of trace elements with the precipitate containing the carrier element, 4) easy determination of the carrier element, 5) correlation between the amount of loss of the carrier element and that of the trace elements after coprecipitation, 6) no interference in the determination of trace elements by the carrier element. The other element, which can be quantitatively coprecipitated with the precipitate, is also used as the internal-standard element. The operation of the precipitate recovery in the rapid coprecipitation technique is simple and rapid compared with that in the conventional coprecipitation method. This paper describes the principle of the rapid coprecipitation technique and its application for the separation and preconcentration of trace elements.