Introduction to the principle and advantages and disadvantages of wet digestion
Wet digestion is a method of destroying organic or reducing substances in a sample with an acid or an alkali solution under heating. Wet digestion is the most direct, effective and economical sample preparation method for elemental analysis.
Principle: Also known as wet ashing or wet oxidation, adding oxidizing strong acid to an appropriate amount of food, and simultaneously heating and decomposing, so that the organic matter is decomposed and oxidized into CO2, water and various gases for accelerated oxidation. A variety of catalysts are added, and this method of destroying organic matter in food is called wet digestion. Biological samples containing large amounts of organic matter are usually wet digested with a mixed acid. Nitric acid with a boiling point above 120 °C is a widely used pre-oxidant, which can destroy the organic matter in the sample; sulfuric acid has strong dehydration ability, can carbonize organic matter, partially degrade the insoluble matter and increase the boiling point of the mixed acid; Chloric acid is the strongest oxidizing agent and dehydrating agent. Due to its high boiling point, it can continue to oxidize the sample after removing the nitric acid. The oxidation of hydrogen peroxide in a mixed acid containing sulfuric acid is based on the formation of peroxymonosulfuric acid, which rapidly decomposes organic substances due to the dehydration of sulfuric acid. When the sample matrix contains more inorganic substances, it is mostly digested with a mixed acid containing hydrochloric acid; and hydrofluoric acid is mainly used to decompose the silicate-containing sample.
Wet digestion advantages : easy to operate, can process a large number of samples at a time, suitable for the analysis of trace metal elements in biological samples.
Disadvantages of wet digestion :
(1) If the sample is completely digested, it needs to consume a large amount of acid, and it needs to be heated at a high temperature (temperature >300 °C if necessary), which causes the wall and reagent to stain the sample. The container used before digestion is 1:1HN03. Heating and washing and subjecting the acid solution used to sub-boiling distillation can remove trace metal element interference therein;
(2) Some mixed acids interfere with the spectrometric determination of the elements after digestion. For example, when the solution contains more HClO4 or H2SO4, it will interfere with the graphite furnace atomic absorption measurement of the element, and the solution can be evaporated to near dry before removal. Such interference.
(3) The wet digestion time is long. For example, pork contains more oil, which is more difficult to digest than vegetables. During the tea digestion process, bubbles will be produced. On the way, it needs to be cooled down. The liquor and rice wine need to be steamed until they are digested. volume.
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