Influence of the species effect on trueness of analytical results estimated by the recovery test when determining selenium by HG-AFS.

The recovery test in the "surrogate" mode is often exploited for trueness assessment when appropriate certified reference materials are not available or to support reference material studies. The species effect occurs when chemical forms of native and surrogate analytes are different. It usually results in obtaining incomparable analytical signals for both forms. Influence of the species effect on the results obtained by "surrogate" recovery test was examined. The examination was performed theoretically on the basis of a extended mathematical model and the results predicted by the model were checked experimentally. Experiments were carried out with the use of synthetic samples containing selenite ions and l-selenomethionine acting as inorganic and organic form of selenium, respectively. Moreover, real samples of thermal spring water and vitamin drink were analysed with the use of flow injection system. The system was dedicated to perform not only spiking but also UV digestion of the synthetic and real samples in order to study the species effect. The system was coupled to hydride generation atomic fluorescence spectrometer (HG-AFS) enabling to determine total amount of selenium.