The microwave digestion system usually refers to the wet digestion that uses microwaves to heat the digestion solution and samples in a closed container, and dissolves various samples quickly under high temperature and pressurized conditions. At present, the technology is widely used in the digestion of various samples in various inspection institutions such as food, medicine, environmental protection, feed, fertilizer, sanitation inspection, geology, chemical industry, etc. Accurate determination of trace, trace and ultra-trace elements in various samples.
Most of them adopt dual control mode of temperature and pressure, and the mode of independent control of temperature or pressure is gradually eliminated by the market. The higher the temperature, the higher the sample reaction speed and the degree of digestion; the higher the pressure, the higher the pressure resistance requirements of the digestion tank, and the higher the relative risk.Therefore, the authenticity and accuracy of the data read by the temperature sensor and the pressure sensor are very important.
Temperature sensors and pressure sensors are important and the most basic configurations. Infrared temperature measurement uses the principle that infrared rays can only penetrate transparent substances to detect the temperature of the sample digestion solution.Therefore, only when the digestion inner tank is made of transparent material can the temperature of the digestion solution be accurately measured.
Sample digestion is inseparable from the use of strong acid or mixed acid, and the automated microwave digestion system generally adopts a closed high temperature and high pressure method to speed up the digestion process, which undoubtedly increases the safety hazards of the sample pretreatment process. Therefore, safety is the priority index for inspecting the instrument.
The safety protection measures of the instrument are generally divided into active and passive methods;
Active safety protection: take measures to eliminate hidden dangers before danger comes;
Passive safety protection: measures that can reduce losses after danger arrives.
Active safety protection is based on prevention, while passive safety protection is based on remedial measures. Therefore, when choosing an instrument, consider the active safety protection measures of the instrument as much as possible, rather than the passive safety protection measures adopted when danger occurs.
Microwave digestion technology is mainly used to help AA, ICP and ICP-MS elemental analysis instruments to obtain complete sample elemental information.Especially for food samples containing volatile elements (such as As, Sb, Pb, Bi, Hg, Se, etc.), good precision and accuracy can be obtained after closed microwave digestion. The characteristics of convenience, speed, completeness, low blank space and simple operation have been realized. However, under the triple pressure of "high temperature, high pressure and strong acid", it is inevitable for experimental operators to have concerns about safety in use. Even if the digestion is over, don't take it lightly, and operate according to the standard.This article introduces some precautions after microwave digestion.
1. Pressure relief after digestion
After microwave digestion , open the door, transfer the rotor to the fume hood, and slowly loosen the air release screw. Note: align the air outlet with the pressure relief baffle.Wait for a while until the acid gas is exhausted, remove the top cover and put the inner tube and ceramic outer tube into the corresponding tube rack.Generally, the lid is opened when the temperature is below 45°C, and acid distillation or constant volume is carried out in order to be suitable for analysis.
2. Clean the top cover, reaction inner tube and constant volume
(1) Open the digestion tank, press the side of the screw cap, and remove the screw cap. Put the inner tube and pressure sleeve into the corresponding tube holder.
(2) Rinse the inside of the sealing cap with a small amount of distilled water for 2 to 3 times, and collect the solution into the digestion tube.
(3) Rinse the sealing cap with a small amount of distilled water for 2 to 3 times and pour it into the digestion solution.
(4) Place the rinsed sealing cap in a clean place to dry.
(5) Make constant volume to the corresponding digestion products.
3.Cleaning of sealing cap and digestion inner tube
(1) After rinsing the inner tube of digestion with distilled water, you can soak it in acid overnight to remove the residue, or you can run the cleaning program.
(2) The O-ring on the inner tube should be removed when catching acid or cleaning.