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What is Acid Digestion for Metal Determination?

By using the techniques of atomic absorption spectrometry and microwave digesters, they comply with traditional methods for acid digestion, and are used for the development and preparation of samples, in order to obtain the analysis in liquid form.

This action is carried out with acids, to achieve complete oxidation and reduce interference caused by organic matter. Because of these, the determination of the metals is developed, heating it in stages, first, the water is eliminated, the product is carbonized and finally incinerated in a muffle furnace.

Likewise, acid digestion offers development mechanisms, accompanied by chemical components, digestion systems and favorable characteristics, for the determination of metals.

Functions of Acid Digestion

The basic principle of acid digestion is related to the oxidative loss of the sample matrix, in which they are usually boiled with an acid at high temperature and remove the substance to be determined, and after analysis.

Therefore, by means of the microwave digester, the samples are dissolved, placing in a concentrated acid inside an airtight container, and exposing it to microwave irradiation, it is possible to determine the material.

Both the rate of thermal decomposition of the sample and the dissolution of the metals increase once they are in solution, and can be quantified by spectroscopic techniques. In the acid digestion process, sample preparation time is reduced by 50 – 75% compared to traditional methods.

It should be noted that acid digestion by microwave offers advantages to accurately record parameters such as pressure or temperature, or the possibility of digesting in very short times, since the heating and cooling rate is very high.

Acid Digestion of Metals

Assisted acid digestion for metal determination, is one of the procedures applied for metal extraction in solid prototypes, involves the use of mineral acids, oxidizers and an external heating microwave source to decompose the sample. The choice of acids, and use of microwaves, depends on the nature of the matrix, among the acids, are:

  • Nitric acid: it is the most recommended for the digestion of samples, where the boiling temperature is relatively low, but with the use of closed containers, is another alternative to increase the temperature and improve the efficiency of digestion.
  • Hydrochloric acid: is a non-oxidant acid with weak reducing properties and is frequently used for the decomposition of inorganic matrices. Dissolves carbonates, phosphates, borates, sulfates (except barium sulfate) and metal oxides.
  • Hydrofluoric acid: is considered an important chemical reagent to improve the decomposition of mineral compounds, and is mixed with other acids, mainly nitric acid.
  • Perchloric acid: it is one of the strongest mineral acids and has a high oxidizing power at high temperatures. It must be handled with extreme care because of its rapid reactivity and can sometimes become explosive. Perchloric acid can be decomposed at 245 °C in a closed microwave container and develop dangerous amounts of gaseous by-products and excess pressure.

Sulfuric acid: is a strong dehydrating reagent, and has the highest boiling temperature of mineral acids used for digestion. For this reason, a long evaporation time is necessary to remove the excess acid.

Kalstein Microwave Digester

At Kalstein, we are able to meet the demands of our users in the selection of laboratory equipment. We offer you the Microwave Digester System, corresponding to the YR series, which has attractive features, such as: The continuous rotor of 360º makes the rotation in the same direction. Ensures even and complete digestion, also reduces engine wear, which greatly prolongs its useful life. The 7-inch color LCD touch screen displays real-time temperature and pressure, as well as working time and trend curves. The material of the sample digestion vessel is imported TFM. For the outer protection container, PEEK and fiberglass are imported which could prevent corrosion by high temperature, high pressure and acid.

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