APPENDIX A 

 DIGESTION PROCEDURE FOR ESTIMATION OF 

 TOTAL SULFUR IN PLANT TISSUE 



REAGENTS 



Magnesium nitrate digestion solution : Place 113 g of MgO in a large 

 Erlenmeyer flask and add 300 ml of demineralized water. Place flask 

 on a magnetic stirrer and insert stirring rod. Very slowly add 465 ml 

 concentrated HNO3 while stirring (CAUTION — the reaction is strongly 

 exothermic and should be carried out under a hood) . Allow 1 to 2 hours 

 for the addition of all of the acid. After cooling, rinse the contents 

 of the flask into a 1-liter volumetric flask and dilute to volume with 

 demineralized water. 



6N HC1 : Add 500 ml of concentrated HC1 to 500 ml of demineralized 

 water. Mix well and allow to cool. 



PROCEDURE 



1. Accurately weigh 0.50 g of the ground plant tissue into a 50-ml 

 beaker or crucible. 



2. Add 5 ml of the Mg(N03) 2/HNO3 solution. Allow to stand a few 

 minutes until all of the plant material is wet. 



3. Evaporate to dryness on a hot plate. Sample must be completely 

 dry to prevent frothing of the sample when placed in the muffle 

 furnace. 



4. Remove from hot plate and place in a muffle furnace. Heat to 

 300°C for 1 hour. Increase temperature to 500°C and muffle for 

 2 additional hours. 



5. Allow sample to cool. Moisten with demineralized water, add 10 ml 

 of 6N HC1, and e\ r aporate to dryness slowly on a hot olate . Be 

 careful that samples do not "bump" resulting in loss of the sample. 



6. Add 5 ml of SN HC1, and heat to dissolve all residue. Remove from 

 hot plate. Carefully wash contents into a 50-ml volumetric flask 

 or test tube calibrated to 50 ml. 



7. Allow sample to cool and dilute co volume. Stopper with a plastic 

 stopper and shake well. 



8. Allow samples to stand overnight and remove an aliquot from the 

 surface or filter through a Whatman no. 42 filter paper. 



9. Determine sulfate S turbidimetricallv. 



168 



