Inanalytical chemistry,ashing orash content determination is the process ofmineralization by completecombustion for preconcentration of trace substances prior to a chemical analysis,[1] such aschromatography, or optical analysis, such asspectroscopy.
The ash content of a sample is a measure of the amount of inorganic noncombustible material it contains. The residues after a sample is completelyburnt - in contrast to theash remaining after incomplete combustion - typically consist ofoxides of theinorganic elements present in the original sample. Ash is one of the components in theproximate analysis of biological materials, consisting mainly of salty, inorganic constituents. It includes metalsalts which are important for processes requiringions such as Na+ (sodium), K+ (potassium), and Ca2+ (calcium). It also includes traceminerals which are required for unique molecules, such aschlorophyll andhemoglobin.
Procedures for ash content determination are similar to procedures forloss 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.
Acrucible can be used to determine the percentage of ash contained in a sample of material such ascoal,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.
TheISO mandates ash content determination for most foodstuffs. Examples include
Examples of ash content methods for the determination of ash in other solids include
Ashing is a test to deduce the amount of ash forming material present in a petroleum product so as to decide its use in certain applications. Ash-forming materials are considered to be undesirable impurities or contaminants.
In the ash analysis of petroleum products, ash content represents the incombustible component remaining after a sample of the furnace oil is completely burned. The ash content of petroleum products is generally low. It is defined as the inorganic residue that remains after combustion of the oil in air at specific high temperature.Ash typically ranges from 0.1 to 0.2% in oil. Some of the ash forming constituents occur naturally in crude oil; others are present as a result of refining or contamination during storage or distribution. Knowledge of the amount of ash-forming material present in a product can provide information as to whether or not the product is suitable application.
In the ash analysis of coal and other solid fuels, the amount of sulfur retained in the ash during the ashing process is not constant, but rather is dependent upon the conditions of ashing as well as the other inorganic constituents in the ash that may form sulfates during the ashing procedure. As such, different ashing procedures may yield different ash contents.[2]
Some necessary apparatus include:
A crucible and its lid are pre-weighed after thorough drying. The sample is added to the completely dry crucible and lid and together they are weighed to determine the mass of the sample by difference. The sample is placed in the hot furnace long enough so that complete combustion of the sample occurs. The crucible, lid and ash then are re-weighed.
The analysis ofhoney shows:[3]
Typical honey analysis
In this example the ash would include all theminerals in honey.
Ashing is also performed prior to chemical analysis byinductively coupled plasma emission spectrometry.
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