May 3, 2008

What is ash content?

What is ash content?
When either organic compounds are decomposed or released at high temperature (500C -600C), the remaining residue is the ash.

This residue consists of oxides and salts containing anions such as phosphates, chlorides, sulfates, and other halides and cations such as sodium, potassium, calcium, magnesium, iron, and manganese.

During the ashing process organic salts decompose, losing the carbon-containing moiety. The metal from such salts forms and oxide or reacts with other anions of the matrix. Some metals (e.g., cadmium and lead) may be volatized during ashing; therefore, if the ash is to be examined for trace elements, care should be exercised to prevent losses during ashing.

For most foods, ashing at 485C or less for 12hrwill give acceptable results for trace elements analysis. Losses of minerals due to carbon release can be appreciable from carbon-containing samples.

This mechanical loss of cash can be avoided by starting the incineration in the muffle furnace at a low temperature (room temperature) and allowing the temperature to rise slowly.

Air currents may be a problem if the door of the furnace is opened suddenly. Generally, samples should not be placed ion areas of the furnace closer than 1 in. from the rear wall and 1.5 in form the front.
What is ash content?

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