Speclflc and accurate determlnatlon of selenium In blologlcal materials can be made by strlpplng voltammetrlc techniques following ion-exchange separation of the element from the bulk of the acid-dlgest matrix. The use of an anion-exchange method enables direct quantltation of selenium In the sample from callbratlon curves rather than by the normally recommended tlme-consuming standard addition method. The separation method descrlbed removes interferences usually encountered from other metal ions and also enables preconcentratlon of the analyte. Differentlal pulse anodic strlpplng vonammetry at a rotatlng gold disk electrode and dlfferentlal pulse cathodic strlpplng voltammetry at a hanging mercury drop electrode gave comparable llmlts of detection for selenium. However the latter approach was adopted because of Its inherently greater reproducibility. Appilcatlon of the method to a range of blologlcal standard reference materlais proved to be very satlsfactory and It Is currently being used for blomedical studies. Selenlum concentratlons less than 1 ng/mL can be determlned by this method.The accurate determination of selenium in biological materials has become increasingly important due to the narrow difference between the concentration range at which it is considered essential (1-5) and that a t which it is known to be toxic (6-8). The estimated (9) and recommended (IO) safe daily intake of selenium for adult humans ranges between 50 and 200 pg; however the daily intake of the element in an average diet is estimated as 62 fig (11). Despite the regular intake of the element, its levels are generally low in human tissues and body fluids. Selenium concentration ranges of 4.8-46 wg/L in urine, 57-320 wg/L in whole blood, 98-327 pg/L in blood serum, 261-410 ng/g in liver, and 100-630 ng/g in kidney have been reported (12). These low concentrations of the element require a highly sensitive, specific, and dependable analytical method for their accurate determination.To date, only a few methods (13-21) provide the necessary reproducibility and sensitivity required for the determination of selenium in biological materials a t the trace to ultratrace levels commonly encountered in biomedical studies. The high sensitivity of the neutron activation technique makes it most attractive, but it is not frequently used because of the specialized techniques, skills, time, and costs involved (2,(22)(23)(24).The comparably high sensitivity of electrochemical techniques such as cathodic and anodic stripping voltammetry provides a far less expensive approach for the determination of selenium in most matrices. Unfortunately matrix effects associated with the determination of selenium in biological materials require that the time-consuming standard addition method is employed with these electrochemical techniques (25-30). This paper describes a method which employs an anion exchange procedure and stripping voltammetry for the determination of selenium in biological materials after acid digestion. Complete removal of the matrix compositi...

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