APPENDIX D 

 AN INDIRECT METHOD FOR THE DETERMINATION OF SULFATES 

 IN SOIL EXTRACTS (FROM HUE AND ADAMS, 1979) 



REAGENTS 



Barium standard: Dissolve 1.9610 g BaSO/vZHoO in 0.1 N HC1 and dilute 

 to a 1-lir.er volume. This solution is a 1,000 ppm Ba stock solution. 

 Prepare a 100 ppm Ba working standard by diluting a 10 ml aliquot of 

 the stock solution to 100 ml with demineralized water. 



C1CH C00H/K0H solution: Dissolve 47.25 g C1CH C00H and 3.40 g K0H in 

 250 ml demineralized water. 



BaS0 / seed suspension: Place 0.1 g BaSO powder in 100 ml demineral- 



ized water. Shake well before each use. 



95% ethanol 



PROCEDURE 



1. Aliquot 10 ml of a 0.01 M Ca(H2P04) 2 ' 2H 2 extract containing 1 to 

 20 ppm sulfate into a 100 ml plastic bottle. 



2. Add 3 ml of a 100 ppm Ba standard. 



3. Add 2 ml of the C1CH 2 C00H/K0H solution 0.1 ml of the BaS0 4 seed 

 suspension, and 15 ml of 95% ethanol. 



4. Cap and shake for 15 minutes. 



5. Transfer to centrifuge tube and centrifuge at 5,000 g_ for 30 mint. 

 at 5°C. 



6. Analyze supernatant for Ba by atomic absorption spectroscopy using 

 a N„0/acetylene flame at an absorption wavelength of 554 nm. 



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