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<br />SELENIUM - SOIL <br />(ASA Agronomy No. 9, Methods of Soil Analysis) <br />Reagents: <br />H2O - distilled - deionized (d & d) <br />HC1 - (Con.) <br />Apparatus: <br />Perkin - Elmer 903 atomic absorption spectrophotometer <br />with recorder. <br />Extraction; <br />1. 64eight 10 g. of soil into a 125 ml COD flask. <br />2. Add 50 ml of d + d H O with a graduated cylinder. <br />Prepare a blank in tl?ie same manner, but delete <br />sample. <br />3. Attach to reflux condensors and boil for 30 minutes. <br />• <br />4. Decant the suspension into a 50 ml centrifuge tube and <br />centrifuge for 15 minutes and decant. <br />5. Transfer a 25 ml aliquot containing 0.0 - 0.6 ug <br />Se with a graduated cylinder into a 250 ml wide <br />mouth erlynmeyer. <br />6. Add 25 ml of HC1 (conc.) so the final volume is at <br />least 6N. <br />7. Prepare 0.5 ug standards. Standards are made by <br />diluting 0.5 ml of 1000 ppm stock Se STD to 1 liter <br />then add 1 ml of this solution to each STD flask and <br />add 24 mis of H2O. Acidify and dilute as in steps <br />5 and 6. <br />8. Weigh 8 g. of Sodium Tetraborohydride and dilute <br />to 100 mis, add t~ao NaOH pellets to this. <br />9. Affix flask to hydride generator and wait 15 seconds. <br />10. Add to flask by syringe 4 mis of solution from step 8, <br />gases will immediately enter into the argon-hydrogen <br />flame on the AA, use the recorder. <br /> <br />11. Aspirate H2O during analyses. <br />12. Prepare calibration curve. <br />6-105 <br />