What is microwave digestion system?
Microwave digestion method
Microwave digestion system
is an instrument system that uses the microwave heating principle to achieve the purpose of sample pre-treatment under high temperature and pressure conditions in a closed vessel.
The core of microwave sample preparation
is to minimize the amount of digestion agent used and reduce the pretreatment time while maximizing the conversion of all elements to be measured into soluble inorganic salts, and reducing the introduction of interfering substances to reduce the difficulty of determining the elements to be measured.Microwave digestion technology
uses the penetrating and activating reaction ability of microwaves to heat the reagents and samples in the closed vessel, which can increase the pressure in the sample preparation vessel and raise the reaction temperature. Thus, it can greatly improve the reaction rate and shorten the time of sample preparation. There are usually closed microwave digesters
on the market because they can improve the reaction speed to complete the sample digestion efficiently and quickly, and let the operation flexibility. The microwave digester
uses a special microwave oven with an industrial all-steel structure, which is different from a household microwave oven. Generally, it adopts top microwave emission heating technology to ensure the uniformity of simultaneous digestion of multiple samples; it uses a large industrial-grade chamber design that can accommodate the simultaneous digestion of 16 samples; it has a multi-layer modified Teflon (PFA) coating sprayed on the inner cavity, which is anti-corrosive, high temperature resistant and has super acid resistance. Microwave digestion system
generally consists of the main engine, fiber optic temperature monitoring system, precise pressure monitoring system, temperature & pressure abnormality monitoring system, digestion tank & rotor system, software system, and other system combinations.
What is microwave?
is one of the abbreviations for a finite band of radio waves, which refers to the frequency of 300MHz-300GHz electromagnetic waves. It is an electromagnetic wave with a wavelength between 1 meter (excluding 1 meter) and 1 millimeter, which means that the wavelength of microwave is between far-infrared and radio waves. It is a collective term for sub-meter, centimeter, millimeter, and sub-millimeter waves, too.Microwave
frequency is higher than the general radio frequency, which is also known as "ultra-high frequency electromagnetic wave". Microwave, as a kind of electromagnetic wave, also has wave-particle duality. The basic properties of microwaves are usually penetration, reflection, and absorption.
Features of microwave digestion system
a. Fast heating, high-temperature rise, and strong ablation ability, greatly shorten the dissolution time of the sample
Different kinds of sample dissolution can be completed within 20 minutes, which is 10-100 times faster than the digestion speed of an electric hot plate. It can also eliminate many samples that are difficult to ablate by conventional methods, such as zircon. The reason for the fast digestion comes from the direct heating of the sample solution by microwaves and the high temperature and pressure that rapidly develops in the tank.
b. Low consumption of solvent elimination and low blanking level
15 ml of the acid solution is typically required to digest a sample, which is only a fraction of the amount of acid used in traditional methods. Due to the closed sample digestion, the acid does not cause volatilization loss, which means there is no need to keep adding acid to maintain the volume of acid.
c. Avoid volatile loss and sample staining, improve the accuracy and precision of analysis, and increase the recovery rate
The use of a closed sample digestion tank avoids the loss of volatile components in the sample or formed during the digestion process, ensuring the accuracy of the measurement results. It also avoids mutual contamination between samples and the external environment, which is suitable for trace and ultra-pure analysis and detection of volatile elements (such as As, Hg). The microwave digestion system can display the three parameters of pressure, temperature, and time in the closed tank during the reaction in real-time. These parameters can be accurately controlled to improve the repeatability, accuracy, and precision of the reaction.
d. Reduced labor intensity and improved working environment
In the past, experimenters needed to boil acid on an electric hot plate to disintegrate samples. Even though there were fume hoods in those days, there was still an acid mist around. Not only were the laboratory personnel exposed to acid mist, but it also corroded other equipment in the laboratory. The sample is now disintegrated in a closed tank, and the volatile acid mist is greatly reduced, effectively improving the working environment of the experimenters. As the speed of sample digestion is accelerated, the analysis time is shortened, while the accuracy and precision of analysis are improved, reducing labor intensity and improving work efficiency.
e. Save power and reduce analysis costs
Using a microwave digestion system can save reagents and electricity. For example, for the digestion of 1 gram of milk powder, the microwave digestion apparatus only takes 8 minutes to complete the digestion by using 800W microwave heating.
Microwave sample preparation system
Microwave sample preparation system includes microwave heating, program control, temperature & pressure control, sample preparation vessels, exhaust systems, sample agitation, exhaust gas monitoring, and exhaust gas treatment. The commonly used technologies are microwave sterilization, microwave extraction, microwave ashing, microwave digestion, etc.
Microwave digestion vessel
Microwave digestion vessels are available in fluoroplastic materials like TFM, PTFE, PFA, and quartz. TFM is a kind of modified PTFE with a melting point of 320℃ to 340℃. Among these materials, TFM is the preferred material for the digestion vessel. PTFE material can only be used for medium and high-pressure digestion tanks, while TFM material can be used for ultra-high pressure microwave digestion tanks.
Acid digestion method
Acid digestion definition
Acid digestion is a common pretreatment method for sediments, sludges, and clays. Most of the sludge samples can be fully ablated with HNO3, and the eliminated substances are all suitable for flame or electrothermal atomic absorption determination.
The acid used in microwave acid digestion is generally nitric acid because its boiling point can rise to 176 ℃ in high pressure (520kPa).
Wet digestion definition
Wet digestion definition
Wet digestion is a method of destroying organic or reducing substances in a sample using an acid or base solution and under heating conditions. The wet digestion method is a direct, effective, and economical way of sample pretreatment for elemental analysis.
Wet digestion procedure
Wet digestion is the process of adding an oxidizing strong acid to the appropriate amount of food and simultaneously heating and cooking to decompose and oxidize organic substances to CO2, water, and various gases. To accelerate the oxidation process, various catalysts can be added at the same time.
Pressure digestion usually requires two steps. In the first step, a tightly sealed crucible container made of Teflon is placed inside a thick-walled stainless steel outer sleeve that is resistant to high pressure; in the second step, the specimen and acid are added to the crucible and then added to the sleeve for heating and decomposition.
Use of microwave digestion system
A. Pre-test preparation
Ensure that the instrument is running properly and that the rotor and the vessel are clean.
B. Weighing sample
The prepared sample should be weighed on a one-millionth balance. The general weighing amount is 0.05-0.5g, but it is better to determine the weighing amount according to the test situation. Weighing principles and considerations are as follows:
a. Ensuring that no sample adheres to the inner tube with the seal or O-ring.
b. The initial test weighing volume of unknown samples should be controlled within 0.1g.
c. The safety of using microwave digestion of unknown samples must be ensured.
d. The weighing volume of active samples should be controlled within 0.1g.
C. Add digestion reagent
The digestion vessels should be placed in a ventilated kitchen and the reagents for digestion should be added and mixed evenly. It is recommended that the total reagent volume be at least 6 ml. Make sure that the volume of solvent and the type of solvent (acid) in each digestion tank are consistent. For organic samples larger than 0.2 g, it is best to place them in the heating equipment for more than half an hour at low temperature to avoid overreaction. It is better to drench the sample from the wall to the bottom of the tube as much as possible.
D. Check the upper cover seal
You should check the seal for breakage. If there is any breakage, replace it in time. The replacement method is as follows.
a. Use a flaring device to make a flaring seal.
b. Put the reaction tube cap on the reaction tube.
c. Place the reaction tube into the ceramic jacket tube. Tighten the top cap and bleeder screw by hand.
d. Place the top cap on the reaction tube so that the bleeder screw is located in the recess of the protective housing.
e. Place the protective cap on the top cap, making sure that the distance between the protective sleeve and the protective cap is less than 2 mm.
f. Be careful not to use excessive force to prevent damage to the threads.
g. Press the seal cover completely onto the seal for at least 3 seconds. A new seal should be pressed for more than 10 seconds.
h. To ensure good sealing, please start the experiment within 15min after flaring, otherwise you need to re-flaring.
F. Cover protection
a. Put the protective cover over the rotor.
b. Align the positioning holes.
c. Screw the cover clockwise.
d. Locked the bayonet.
G. Microwave digestion method
Turn on the power and enter the main program menu. You should start to write the program based on the sample requirement. For details, please refer to the product manual.
H. Pressure relief
When the digestion is finished, you should open the door, transfer the rotor to the fume hood and slowly loosen the bleed screw. (Note: Align the outlet hole with the pressure relief baffle.) When the acid gas is exhausted, you should remove the top cover and put the inner tube and the ceramic outer tube into the corresponding tube rack. Generally, it is better to open the lid at or lower 45°C.
I. Clean the top cover and the inner reaction tube
a. Open the digestion vessel, press the side of the threaded cap, and remove the threaded cap. Place the inner tube and pressure sleeve into the corresponding tube holder.
b. Rinse the sealed cap with a small amount of distilled water 2 to 3 times and pour it into the digestion solution.
c. Place the rinsed sealed lid in a clean place to dry.
d. Fix the volume of the corresponding digestion products.
J. Clean the sealing cap and the inner tube of the digestion
a. After the digestion inner tube has been rinsed with distilled water, you can soak the acid overnight to remove the residue, or you can add 6mL HNO3 to run the cleaning procedure.
b. The O-ring on the inner tube should be removed when the acid is driven or cleaned.
How to buy microwave digestion system?
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