What happens to non volatile compounds in muffle furnace?
Answers
Dry ashing is an alternative means of sample preparation and is accomplished by heating the sample in an open dish or crucible in air. Very often this is done in a muffle furnace located in a clean room. The stages of dry ashing include: sample drying, evaporation of volatile materials, and progressive oxidation of the non-volatile residue until all of the organic matter is destroyed. Ashing aids are sometimes added to samples to accelerate the oxidative process and/or prevent volatilization of the element of interest from the ash. Dry ashing offers the advantages of requiring few reagents, utilizing simple apparatus, lending itself to batch sample preparation and requiring limited operator attention. Table 13.3 outlines the dry ashing procedure which is routinely utilized in the author’s laboratory for successful chromium determinations. Dry ashing is very often used for biological fluids. In some instances, unoxidized material remains after dry ashing overnight, in those cases the sample may be treated with hydrochloric or nitric acid, dried, and returned to the furnace to complete the ashing step.
Table 13.3. Dry Ash Preparation Procedure (Nutrient Composition Laboratory)
1. Pipet 2 ml of serum into a silanized quart test tube.
2. Add 20 μl of 11% magnesium nitrate and gently vortex.
3. Freeze samples at –20 °C then freeze-dry overnight.
4. Place samples in muffle furnace and heat: 100 °C 1 hour; 150 °C 1 hour; 200 °C/hour; 250 °C 1 hour; 480 °C overnight.
5. Dissolve ashed sera in 0.5 ml 5% sub-boiling distilled nitric acid.