Ashing Sample Preparation Procedures

Ashing in analytical chemistry is defined as the heating of a substance to leave only noncombustible ash, which is analyzed for it's elemental composition.

Ashing Techniques

The sample preparation techniques incorporating some form of 'ashing' are as follows:

Dry Ashing

Dry Ashing is usually performed by placing the sample in an open inert vessel and destroying the combustible (organic) portion of the sample by thermal decomposition using a muffle furnace. Typical ashing temperatures are 450 to 550 °C. Magnesium nitrate is commonly used as an ashing aid. Charring the sample prior to muffling is preferred. Charring is accomplished using an open flame.

Sulfated Ashing

Sulfated Ashing involves treatment of the sample after charring using an open flame with sulfuric acid (the char is wetted using the minimum amount of sulfuric acid and then brought to dryness before muffling) and then placing in a muffle furnace.

Wet Ashing

Wet Ashing is treatment of the sample with a moderate amount of sulfuric acid before charring. Charring is performed using an open flame. Liquid samples tend to foam. After the excess sulfuric acid is driven off, the sample is muffled as above.

Low-temperature Ashing

Low-temperature Ashing involves treatment of the sample at ~ 120 °C using activated (singlet state) oxygen.

Closed System Ashing

Closed System Ashing involves thermal decomposition in oxygen in a closed system such as a Schöniger flask or an oxygen Parr bomb.

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