The ash content of a sample is a measure of the amount of inorganic noncombustible material it contains. The residues after a sample is completely burnt - in contrast to the ash remaining after incomplete combustion - typically consist of oxides of the inorganic elements present in the original sample. Ash is one of the components in the proximate analysis of biological materials, consisting mainly of salty, inorganic constituents. It includes metal salts which are important for processes requiring ions such as Na (sodium), K (potassium), and Ca (calcium). It also includes trace minerals which are required for unique molecules, such as chlorophyll and hemoglobin.
Procedures for ash content determination are similar to procedures for loss on ignition. Typically, the term ash is used for primarily organic material such as fuels and foodstuffs, while the term loss on ignition is used for primarily inorganic material such as rocks and combusted ash.
A crucible can be used to determine the percentage of ash contained in a sample of material such as coal, wood, oil, rubber, plastics, foodstuffs, or any burnable material. The appropriate method for ash determination varies depending upon the type of sample analyzed. Each method may vary in parameters such as furnace temperature, residence time in the furnace, number of heating steps, and sample preparation procedures.
The ISO mandates ash content determination for most foodstuffs. Examples include
* ISO 2171: Cereals, pulses and by-products — Determination of ash yield by incineration;
* ISO 3593: Starch — Determination of ash;
* ISO 928: Spices and condiments - Determination of total ash; and
* ISO 936: Meat and meat products - Determination of total ash.
Examples of ash content methods for the determination of ash in other solids include
* ASTM D482: Standard Test Method for Ash from Petroleum Products;
* ISO 6245: Petroleum products — Determination of ash;
* ASTM D874: Standard Test Method for Sulfated Ash from Lubricating Oils and Additives;
* ASTM D3174: Standard Test Method for Ash in the Analysis Sample of Coal and Coke from Coal;
* ISO 1171: Solid mineral fuels — Determination of ash;
* ISO 18122: Solid biofuels — Determination of ash content;
* ASTM D1102: Standard Test Method for Ash in Wood;
* ASTM D2974: Standard Test Methods for Determining the Water (Moisture) Content, Ash Content, and Organic Material of Peat and Other Organic Soils;
* ASTM D2866: Standard Test Method for Total Ash Content of Activated Carbon;
* ISO 3451: Plastics — Determination of ash — Part 1: General methods;
* ASTM D2584: Standard Test Method for Ignition Loss of Cured Reinforced Resins; and
* ASTM D5630: Standard Test Method for Ash Content in Plastics.