Suggested Modified Method for Colorimetric Determination of Selenium in Natural Water

Abstract

This paper begins by providing a brief overview of the development of methods for the determination of selenium. Results of a study by Cheng in 1956 found that at a pH greater than 5, piazselenol could be quantitatively extracted with toluene, benzene, or xylene, butyl, and amyl alcohols and that ethylenediaminetetraacetic acid tetrasodium salt (EDTA) can be used to minimize the interference of polyvalent metals. The objective of the study described in detail in this paper was concerned essentially with reproducing Cheng's results and adapting his method to the field of water chemistry. The modified method presented here can be used for 0‐50 μg selenium with good results. When the single‐extraction technique is used for simplicity, approximately 60 per cent of the selenium is extracted. The results are, therefore, largely empiric, and care must be taken to insure that operating conditions are kept as nearly constant as possible. Experimental apparatus is described, along with reagents used in the study, the procedure, experimental results, calculations, and precision and accuracy. Conclusions indicate that the removal of water from the toluene layer can be accomplished by filtering through 100 mg anhydrous sodium sulfate on No. 40 filter paper. This method is quicker than the centrifuging recommended by Cheng, and a comparison of both methods shows no difference. The diaminobenzidine reagent can be added either in the solid form or as a solution. It is easier to use the reagent in solution, provided only enough is made up for a few days at a time.

Fluorometric Determination of Selenium in Plants and Animals with 3,3´-Diaminobenzidine.

“…of aqueous phase and 5 ml. of toluene indicated that a recovery of 74 ±2% would be obtained with one extraction; there is no advantage (14) in attempting to increase the per cent extracted by increasing the number of extractions, because the volume of the organic phase will also be increased.…”

“…Handley and Johnson (7) have used the same reaction with plant material and report that 0.25 Mg. of Se may probably be determined with confidence. Magín et al (14) use this method for measuring Se in water.…”

Selenium in waters in and adjacent to the Kendrick Project, Natrona County, Wyoming

“…The water samples were analyzed by the U.S. Geological Survey laboratory in Worland, Wyo., using the method described by Magin, Thatcher, Rettig, and Levine (1960). The accuracy of the determination is somewhat sensitive to interference from other minerals at high concentrations of total dissolved solids.…”