In recent years, microwave digesters have been widely used, and most users are proficient in operating the instrument. Today, we will discuss with you about its detection principle and structure, so as to make the microwave digester easier.
The basic properties of microwaves usually present three characteristics: reflection, penetration, and absorption. This electromagnetic wave has the properties of visible light and travels in a straight line. When encountering metal materials (such as copper, iron, aluminum, etc.), it will reflect like a mirror. When encountering insulators such as glass, ceramics, plastics (polyethylene, polystyrene), Teflon, quartz, paper, etc., they will pass through them as smoothly as light passes through glass. When encountering a polar molecular dielectric (such as protein, fat, etc.containing water), microwaves cannot pass through, but will be absorbed in a large amount, and the absorbed electromagnetic energy will be converted into heat energy.
Microwaves are generated by magnetrons, which are microwave generators that can generate ultra-short electromagnetic waves, that is, continuously change the direction of molecular polarity at a rate of 2.45 billion vibrations per second, causing molecules to produce high-speed collisions and frictions.Vigorous exercise generates a lot of heat energy. Microwave digester technology is to use microwave penetration and activation reaction ability to heat reagents and samples in airtight containers, which can increase the pressure in the sample preparation container and increase the reaction temperature, thereby greatly increasing the reaction rate and shortening the sample preparation time.
The microwave digester is mainly composed of a magnetron, a waveguide, a microwave cavity, a load plate, an automatic monitoring system, an exhaust system, a safety door, a microwave digestion tank, and a temperature and pressure control tank.
1. Body heating
When the electric furnace is heated, the energy is transmitted through heat radiation, convection and heat conduction.The heat is transferred from the outside to the inside through the wall of the sample, and the sample is heated by heat conduction.Microwave heating is a direct body heating method.Microwaves can penetrate into the interior of the test solution, and at different depths of the sample, the microwave will generate thermal effects at the same time, which not only makes the heating faster, but also more uniform.The heating time is greatly shortened, which is faster and more efficient than traditional heating methods.For example, oxides or sulfides can be heated to hundreds of degrees Celsius within 1 minute under the action of microwaves.In traditional heating methods (thermal radiation, conduction and convection), the utilization of heat energy is low, and a lot of heat is dissipated to the surrounding environment, while microwave heating directly acts on the interior of the material, thus improving the energy utilization rate.
2. Overheating phenomenon
Microwave heating can also cause superheating (ie, higher than the boiling point temperature). When the electric furnace is heated, the heat is conducted from the outside to the inside through the wall to the sample, and bubbles are easily formed on the surface of the wall, so it is not easy to overheat, and the temperature is kept at the boiling point, because gasification needs to absorb a lot of heat.In the microwave field, the "heat supply" method is completely different, and the energy is directly converted inside the system.Due to the lack of "core" to form gas "bubbles" inside the system, some reagents with low boiling points are prone to overheating in closed containers.It can be seen that the reagents in the closed sample dissolution tank can provide higher temperatures.Facilitate the digestion of the sample.
Since the polar molecules of the reagent and the sample change their orientation rapidly with the changing electromagnetic field in the electromagnetic field, the molecules collide with each other and rub against each other, which means that the surfaces of the reagent and the sample are constantly updated, and the surface of the sample is constantly in contact with new reagents. Accelerate the chemical reaction between the reagent and the sample. The alternating electromagnetic field is equivalent to a high-speed stirrer, which increases the rate of chemical reactions and speeds up digestion. From this synthesis, microwave heating is fast, uniform, superheated, and constantly produces new contact surfaces. Sometimes it can also reduce the activation energy of the reaction, change the kinetics of the reaction, increase the capability of the microwave digester, and digest many samples that are difficult to digest by traditional methods.