How to Choose a Microwave Digestion Instrument

"MicroWave Digestion Makes a Big Difference: How to Choose a High-Throughput Microwave Digestion System"

Currently, high-throughput microwave digestion systems are widely used in environmental safety testing and food safety testing. "High-throughput" refers to a batch processing capacity of ≥40 units. The tank structure of the digestion vessels and the customer's sample preparation as well as their requirements for equipment safety are vastly different from those of the "super high-pressure microwave digestion systems" which only have a few dozen or even several digestion vessels!

In short, there are at least the following points:

The "High-Throughput Microwave Digestion Vessel" has a batch processing capacity of ≥40 vessels, distributed in at least 2 circles, and even up to 3 circles. This inevitably leads to temperature differences in the vessels due to the energy difference between the inner and outer circles and the difference in heat dissipation rates. At this point, using the temperature of one master vessel to represent the temperature of the remaining 39 vessels raises the question of its representativeness.

Customers who purchase "high-throughput microwave digestion tanks" typically have a large volume of samples to be tested, with a high demand for sample processing efficiency. The samples may vary greatly in nature, and their composition is unlikely to be uniform. When different samples are digested in the same batch, the temperature and pressure changes within each reaction tank differ, making it obvious that the temperature and pressure of a master tank cannot represent those of the remaining 39 tanks!

3. Dissolving ≥40 sample cans simultaneously significantly increases safety risks due to overheating and overpressure compared to the "super-high-pressure tank" model that processes 6-16 cans per batch. In this case, "full-tank infrared temperature measurement" and "full-tank pressure control" become particularly crucial for ensuring safety!

4. The "High-Throughput Microwave Digestion Vessel" is structurally simpler and more user-friendly, with lower operational costs compared to the "Ultra-High Pressure Microwave Digestion Vessel." However, the "High-Throughput Microwave Digestion Vessel" demands higher accuracy in temperature control and operational safety.

There's no doubt that the use of "full tank temperature control" and "full tank pressure control" methods is crucial for ensuring the safety and dissolution efficiency of high-throughput microwave digestion systems. But are all high-throughput microwave digestion systems that claim to use these methods identical? Clearly not, there's a lot of nuance involved.

Full罐Temperature Control

The principle of "Full Tank Temperature Control" (Full Tank Temperature Regulation) involves using infrared temperature sensors to individually scan each digestion tank, collecting the surface temperature of the material and converting it into the internal solution temperature of the tank through a coefficient, or directly collecting the internal solution temperature by transmitting through the tank material (mid-infrared technology). This method enables the acquisition of temperature data for all digestion tanks and their control. Setting aside whether the conversion coefficients are applicable to all different types of samples, the infrared technology itself varies among brands (low-sensitivity near-infrared technology, high-sensitivity near-infrared technology, and mid-infrared technology with higher accuracy). Additionally, there are significant differences in the placement and quantity of infrared sensors (single-point infrared on the side wall for non-full tank temperature measurement, single-point infrared on the bottom for non-full tank temperature measurement, and dual infrared on the bottom for full tank temperature measurement). The actual performance of equipment from different brands varies greatly, as detailed below:

1. Low-sensitivity near-infrared technology + side wall single-point infrared non-full-tank temperature measurement: (as shown in Figure 1) This initial temperature measurement method is cost-effective and has a simple main unit and tank structure design; however, it is not a full-tank measurement, only detecting the outer wall temperature of the tank's protective sheath. The temperature measurement points are not located in the sample reaction area, resulting in extremely low accuracy. The detection data cannot reflect the internal tank temperature and can only be used for tank temperature anomaly alarms.

2. High-sensitivity near-infrared technology + bottom double infrared full-tank temperature measurement: This method is an earlier adopted full-tank temperature measurement technique, with a higher cost. Moreover, since it measures the surface temperature of the material in the bottom reaction zone of the tank, rather than the internal solution temperature, it is greatly influenced by the thickness and usage level of the tank material.

3. High Accuracy Mid-Infrared Technology + Bottom Dual Infrared Full Tank Temperature Measurement: This full tank temperature measurement method, currently used only in Yiyao Technology and a certain imported brand's models, is named simply as "Mid-Infrared Temperature Measurement Technology," just like Yiyao's down-to-earth approach. This innovative bottom dual mid-infrared temperature measurement technology can penetrate through the tank material to directly detect the internal solution temperature of the bottom reaction zone, offering extremely high accuracy, although it comes with a higher cost.

Full Can Pressure Control

The "Full罐PressureControlSystem" (Full Tank Pressure Control) operates on the principle of a reusable "quantitative" or "non-quantitative" automatic pressure relief technology for each digestion tank. Should the tank's internal pressure exceed safe levels during the reaction process, the tank can automatically release excess pressure, thereby preventing any tank from experiencing an over-pressure explosion incident. It is important to note that the pressure relief we refer to is a safe, non-destructive process. In the absence of any pressure relief ports, if the pressure surpasses the limit, the top thread or gasket would release pressure destructively, which, even disregarding the consumables affected by the pressure relief, poses greater safety risks. Additionally, the system features an "acoustic abnormal sound alarm" and an "acid gas concentration alarm" integrated into the microwave digestion instrument's main unit. In the event of a widespread over-pressure release in the tank within the chamber, the main unit will automatically shut down and trigger an alarm. Compared to a single main control tank pressure control, this approach offers clear advantages in pressure control for high-throughput microwave digestion instruments and is widely adopted by nearly all microwave digestion instrument manufacturers. Of course, the implementation methods among different brands still vary.

1. Non-quantitative cylinder automatic relief technology + sound abnormality alarm: This initial full cylinder pressure control method features a simple cylinder structure and low manufacturing cost, primarily releasing pressure through the deformation of sealing components. However, this method is greatly affected by material usage degree and aging, as the pressure relief point is "vague" with pressure from 10atm to 20atm, leading to excessive total pressure relief and consistently low internal pressure. This prevents achieving reaction temperatures above 190℃, making it impossible to clarify oil samples, and resulting in a low data recovery rate!

2. Quantitative Vessel Automatic Pressure Relief Technology: As an upgraded new full-vessel pressure control technology, each digestion vessel cover is equipped with a reusable "quantitative pressure control module." The pressure relief "boundary" is set at 20 atm, and the "quantitative pressure control module" automatically initiates pressure relief only when the vessel's internal pressure exceeds 20 atm. Once the pressure falls below 20 atm, the "quantitative pressure control module" automatically seals again to ensure the vessel's密封ity. This structure supports operation temperatures above 210°C for digestion vessels, significantly enhancing sample digestion effectiveness, allowing for clear dissolution of oil samples, and ensuring data recovery rates! Of course, due to the complex vessel structure, the manufacturing cost is also high.