Sample size:  Ideal sample size is between 0.6 to 0.8 g.  Over 1.0 g ashing might not be complete.  Some question about precision if samples are smaller than 0.2 g.

Procedure:  Place samples in muffle furnace and heat to 155 C and hold for 45 min.  Increase heat to 255 C and hold for 30 min.  Increase heat again to 380 C and hold for 30.  Finally increase temperature to 540-550 C for 4 hr.  Increasing temperature in increments keeps the samples from flaming which will cause the loss of sample.  Because of that, the door should not be opened during the ashing process.

Desiccators

Prepare silica desiccant (heat in an oven between 200-225 F until indicator is blue) and pour into bottom of desiccator.  Make sure lid seals completely.  Keep lid on desiccator except while transferring samples or crucibles.  Recharge silica desiccant as necessary.

Ashing Procedure

1. Dry numbered crucibles are stored in a desiccator.
2. Weigh each crucible & record weight.  Tare balance.
3. Weigh crucible and root sample and record weight.
4. Place crucible and sample into muffle furnace.
5. Close door.
6. Follow Root Ash Procedure.
7. Turn off muffle furnace and open door 1”-2” to allow heat to escape.
8. Move crucibles (using tongs) onto heat resistant lab bench to allow to become less hot.
9. Transfer samples in hot crucibles (using tongs) into desiccator and seal.
10. Allow desiccator to cool, vacuum will occur.
11. Weigh each crucible with ash & record weight.
12. Determine sensitivity of weight necessary (for very small samples).
13. Discard ashed sample and clean crucibles.
14. Dry crucibles and store in a desiccator.

14 January 2000