Under
standing the speciation of the multioxidation statesof selenium is vital to predicting the mineralization,mobilization, and toxicity of the trace element in naturalsystems. A sequential extraction scheme (SES) wasdevelopedfor identification of Se oxidation states that firstemployed0.1 M (pH 7.0)K
2HPO
4-KH
2PO
4(P-buffer) to releasesoluble selenate (Se
+VI) and selenide(Se
-II) and ligand-exchangeable selenite (Se
+IV). The second stepinvolvedoxidation of organic materials with 0.1 MK
2S
2O
8 (90
![](/images/entities/deg.gif)
C)to release Se
-II and Se
+IVassociated or occluded with organicmatter. The final step used HNO
3 (90
![](/images/entities/deg.gif)
C) tosolubilizeinsoluble Se remaining in the sample. The solubilizedSecompounds were speciated by a selective hydridegeneration atomic absorption spectrophotometry technique.Accuracy of the developed SES method (96-103%recovery)was verified by use of prepared Se compounds of knownspeciation, NIST
standard reference materials, andexistingseleniferous soils. The average precision (relative
standarddeviation) for the P-buffer extraction ranged from 5.5 to7.7% (
n = 12); the precision of the persulfate extractionrangedfrom 2.6 to 8.4% (
n = 12); and the precision of thenitricacid extraction ranged from 2.8 to 7.4% (
n = 12) forthree soilsextracted at four different time periods. The methodwasapplied to analyze Se species in seleniferous plant, soil,and sediment samples.