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Key points of sample digestion

●Digestion temperature

●Digestion time

●Digestion solution

The right digestion solution and digestion temperature are the key to ensure that the sample can be chemically reacted and digested, and the digestion time ensures that the sample is completely digested, usually with a low-power multi-step heating and pressure ramp-up program.

It is necessary to understand the components in the sample matrix and determine the effective temperature at which the sample is decomposed, and a good understanding of the digestion characteristics, sample components, and interactions between different reagents can make it easier for the user to control the digestion process of the sample.

For different organic or inorganic samples, the intensity of the chemical reaction and the change of physical equivalence at each temperature point during acid digestion are different.

Below is the sharing from Welso for your reference:

●Organic samples of carbohydrates, proteins and lipids are the three matrix components of the animal and plant samples. In the microwave digestion of the animal and plant samples, high pressure can be produced by the gas by-products such as CO2 and NO2. In general, the critical temperature of the organic sample is digesting by nitric acid(HNO3) as follows:

▲Carbohydrates, such as starch, >140℃;

▲Proteins, >145-150℃;

▲Sugars, >150℃;

▲Lipids and fats,> 160-165℃;

▲Heavy oil and petroleum bitumen, >180-185℃;

●The digestion of inorganic samples needs to be reacted with the corrosive mixed acid at high temperature to achieve complete digestion. The pressure of the inorganic sample is lower than that of organic samples, most inorganic samples without CO32- can be digested completely around 185℃, and can digest under the program only one step.

●For microwave digestion, the selection of reagents is very important. The digestion of organic samples needs to maintain the acid condition of strong oxidizing, mixed digestion reagents are commonly used, such as HNO3/H2O2、HNO3/H2O2/HF、HNO3/HCl, etc.

●HNO3, H2SO4 and HCl are commonly used in wet digestion method. This is due to sulfate and chloride of some metals are insoluble or slightly soluble, and boiling point for H2SO4 is high which will easily cause damage to digestion vessel because of too high temperature, so microwave digestion mostly use HNO3. Advantage forHNO3is that all nitrate are soluble to water and strong oxidants which makes organics easy to digest. Moreover, boiling point for HNO3（120℃）is low which is in safe temperature range (≤250℃). HF makes soil and sediments easy to digest and has little effect on bio-samples. H2O2,as weak acid oxidizer which resolve into high energy state reactive oxygen can degrade some organics like humic acid. If user use H2O2 and HNO3 together can improve oxidizingability and damage organics which results in easy digestion and little effect on reaction matrix.

●It is common to use HNO3/H2O2 for food and cosmetics samples; HNO3/HF，HNO3/HCl/HF for environment samples; HNO3/H2O2，HNO3/HF，HNO3/HCl for biological and pharceutical samples;HNO3/HF，HNO3/HCl，HNO3/HCl/HF for geological mineral samples or industrial samples.

With the development of society and the improvement of productivity, requirements for sample detection and analysis are higher and higher. Traditional digestion method often requires a lot of time and manpower, and the operation is cumbersome while the results are inaccurate. Microwave digestion system perfectly solves the problems of traditional digestion methods, which achieves the perfect combination of high performance and high throughput, making sample digestion rigid, efficient, safe and environmentally friendly.