Microwave digestion is a chemical technique used to decompose sample material into a solution suitable for quantitative

elemental analysis Elemental analysis is a process where a sample of some material (e.g., soil, waste or drinking water, bodily fluids, minerals, chemical compounds) is analyzed for its elemental and sometimes isotopic composition. Elemental analysis can be qualita ...

via inductively coupled plasma mass spectrometry (ICP-MS), atomic absorption spectroscopy, or atomic emission spectroscopy (including

ICP-AES Inductively coupled plasma atomic emission spectroscopy (ICP-AES), also referred to as inductively coupled plasma optical emission spectroscopy (ICP-OES), is an analytical technique used for the detection of chemical elements. It is a type of emiss ...

). It is commonly used in analyses for

heavy metals upright=1.2, Crystals of osmium, a heavy metal nearly twice as dense as lead">lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead Heavy metals are generally defined as ...

Generally, sample material is combined with a concentrated strong acid or a mixture thereof, most commonly using

nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...

hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid Acid strength is the tendency of an acid, symbol ...

and/or

hydrofluoric acid Hydrofluoric acid is a Solution (chemistry), solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly Corrosive substance, corrosive. It is used to make most fluorine-containing compounds; examples include th ...

, in a closed vessel. The vessel and its contents are then exposed to

microwave irradiation Microwave chemistry is the science of applying microwave radiation to chemical reactions. Microwaves act as high frequency electric fields and will generally heat any material containing mobile electric charges, such as polar molecules in a solvent ...

, raising the pressure and temperature of the solution mixture. The elevated pressures and temperatures within a low pH sample medium increase both the speed of thermal decomposition of the sample and the

solubility In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubil ...

of elements in solution. Organic compounds are removed during decomposition. Once these elements are in solution, it is possible to quantify elemental concentrations within samples. Microwaves can be programmed to reach specific temperatures or ramp up to a given temperature at a specified rate. The temperature in the interior of the vessel is monitored by an

infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

external sensor or by a optic fiber probe, and the microwave power is regulated to maintain the temperature defined by the active program. The vessel solution must contain at least one solvent that absorbs microwave radiation, usually water. The specific blend of acids (or other reagents) and the temperatures vary depending upon the type of sample being digested. Often a standardized protocol is followed, such as an Environmental Protection Agency Method. Before microwave digestion technology was developed, samples were digested using less convenient methods, such as heating vessels in an oven, typically for at least 24 hours. The use of microwave energy allows for fast sample heating, reducing digestion time to as little as one hour.

References

Footnotes

Bibliography

* {{DEFAULTSORT:Microwave Digestion Analytical chemistry