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TITLE:  Colorimetric determination of selenium in mineral premixes
 
AUTHORS:  Hurlbut JA;Burkepile RG;Geisler CA;Kijak PJ;Rummel NG;
 
YEAR:  1997
 
JOURNAL ABBREV:  J AOAC Int
 
MONTH:  Jul
 
TYPE:  JOUR
 
REFMAN INDEX:  81
 
JOURNAL FULL:  Journal of AOAC International
 
VOLUME:  80
 
ISSUE:  4
 
START PAGE:  709
 
END PAGE:  716
 
KEYWORDS:  3,3'-Diaminobenzidine;analysis;Animal Feed;Animals;Azoles;Calcium;Calcium Carbonate;chemistry;Colorimetry;Edetic Acid;Ferric Compounds;Food;Food Additives;Food Analysis;Hydrogen-Ion Concentration;isolation & purification;Laboratories;Magnesium;Nitric Acid;Organoselenium Compounds;Selenium;Selenium Compounds;Silicon Dioxide;Sodium;Sodium Selenite;Spectrophotometry,Ultraviolet;standards;Toluene;Water;
 
ABSTRACT:  A method is described for determination of sodium selenite or sodium selenate in mineral-based premixes. It is based on the formation of intense-yellow piazselenol by Se(IV) and 3,3'-diaminobenzidine. Mineral premixes typically contain calcium carbonate as a base material and magnesium carbonate, silicon dioxide, and iron(III) oxide as minor components or additives. In this method, the premix is digested briefly in nitric acid, diluted with water, and filtered to remove any Iron(III) oxide. Ethylenediaminetetraacetic acid and HCl are added to the filtrate, which is heated to near boiling for 1 h to convert any selenate to selenite. After heating, the solution is buffered between pH 2 and 3 with NaOH and formic acid and treated with NH2OH and EDTA; any Se present forms a complex with 3,3'-diaminobenzidine at 60 degrees C. The solution is made basic with NH4OH, and the piazselenol is extracted into toluene. The absorbance of the complex in dried toluene is measured at 420 nm. The method was validated independently by 2 laboratories. Samples analyzed included calcium carbonate fortified with 100, 200, and 300 micrograms Se in the form of sodium selenite or sodium selenate, a calcium carbonate premix containing sodium selenite, a calcium carbonate premix containing sodium selenate, and a commercial premix; 5 replicates of each sample type were analyzed by each laboratory. Average recoveries ranged from 89 to 109% with coefficients of variation from 1.2 to 13.6%
 
AFFILIATIONS:  Metropolitan State College of Denver, Chemistry Department, CO 80217-3362, USA
 
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