Fully automatic digestion instrumentfeature1. In terms of digestion, microwave-assisted chemical technology has a fast digestion speed, processing a batch of samples 10-100 times faster than the general electric heating plate method
2. Good digestion effect, using high-pressure sealed container while microwave heating, sample digestion *, especially effective for difficult to hold samples
3. The sample is digested in a closed digestion tank, greatly reducing the loss of volatile elements. Therefore, making the analysis results more accurate
4. Microwave digestion uses fewer reagents, reducing the blank value and background of the sample
5. The entire digestion process is carried out under sealed conditions, and the acidic reagent will not pollute the environment, which is beneficial for environmental protection and personal health
6. The energy-saving effect is very significant, saving about 80% energy compared to traditional methods
7. The parallelism and repeatability of samples processed in the same batch are good, avoiding errors caused by human operation
Weigh 0.2g-1.0g of the sample and place it in a digestion tank. Add about 2mI of water and an appropriate amount of acid. Usually, HNO3, HCI, HF, H2O2, etc. are used to cover the tank and put it into the furnace. When microwaves pass through the sample, polar molecules rapidly change their orientation with the microwave frequency. At 2450MHz, the molecules change direction 2.45 × 109 times per second, rotating back and forth and colliding and rubbing with surrounding molecules. The total energy of the molecules increases, causing a sharp rise in the sample temperature. At the same time, charged particles (ions, hydrated ions, etc.) in the test solution undergo back and forth movement under the action of electric field force in the alternating electromagnetic field, and also collide with adjacent molecules, causing the temperature of the sample to rise. This heating method is completely different from the traditional electric furnace heating method.
(1) Body heating. When the electric furnace is heated, energy is transferred through thermal radiation, convection, and heat conduction. Heat is transmitted from the outside to the inside through the wall of the device to the sample, and the sample is heated through heat conduction. Microwave heating is a direct method of body heating, where microwaves can penetrate into the interior of the test solution,
At different depths of the sample, the microwave simultaneously generates thermal effects wherever it goes, which not only makes heating faster but also more uniform. Greatly reducing the heating time, it is faster and more efficient than traditional heating methods. For example, oxides or sulfides can be heated to several hundred degrees Celsius within 1 minute under the action of microwave (2450MHz, 800W). For example, 1.5 grams of Mn02 can be heated to 920K at 650W microwave for 1 minute, indicating a very fast heating rate. In traditional heating methods (thermal radiation, conduction, and convection), the utilization of thermal energy is relatively low, and a lot of heat is dissipated to the surrounding environment. However, microwave heating directly acts on the interior of the material, thus improving energy utilization efficiency.
（2）Overheating phenomenon. Microwave heating can also cause overheating (i.e., exceeding the boiling point temperature)
High). When heating in an electric furnace, heat is conducted from the outside to the inside through the vessel wall to the sample. Bubbles are easily formed on the surface of the vessel wall, making it less prone to overheating. The temperature is maintained at the boiling point because gasification absorbs a large amount of heat. In the microwave field, the heating method is different, and energy is directly converted within the system. Due to the lack of a "core" for forming gas bubbles within the system, some low boiling point reagents are prone to overheating in closed containers. It can be seen that reagents in closed dissolution tanks can provide higher temperatures, which is beneficial for sample digestion.
(3) Stir. Due to the rapidly changing orientation of polar molecules in the 2450MHz electromagnetic field of both the reagent and the sample, molecules collide and rub against each other, which is equivalent to the continuous renewal of the surfaces of the reagent and the sample. The sample surface constantly comes into contact with new reagents, accelerating the chemical reaction between the reagent and the sample. The alternating electromagnetic field is equivalent to a high-speed stirrer, stirring 2.45 × 109 times per second, which increases the rate of chemical reactions and accelerates digestion. Thus, microwave heating is fast, uniform, overheated, and constantly generates new contact surfaces. Sometimes it can also reduce the activation energy of the reaction, change the reaction kinetics, and enhance the microwave digestion ability, which can digest many samples that are difficult to digest by traditional methods.
As discussed above, the speed of heating and digestion is not only related to the power of the microwave, but also to the composition and concentration of the sample, as well as the type and amount of acid used as the reagent. To digest a sample in a short period of time, appropriate acid, microwave power, and time should be selected.