The principle of liquid chromatography-mass spectrometry is to separate substances from the liquid phase and analyze them using a mass spectrometry detector. The liquid phase separates liquid and molecular substances, which are then transformed into gas phase charged ions through a heated and high-voltage ion source in mass spectrometry. If high-purity nitrogen gas is present, it can accelerate solvent evaporation at the ion source site, promote the formation of gas phase charged ions, and act as a drying gas. In triple quadrupole mass spectrometry, high-purity nitrogen serves as a collision gas to collide and shatter ions, facilitating the formation of quantitative ions in the compound to be analyzed.
SCIEX's liquid gas supply includes three types of gas: Gas1Gas2, Curtain gas, and exhaust gas. Gas1 is an atomizing gas used for atomization and solvent removal; Gas2 is an auxiliary gas that causes charged droplets to form gas-phase charged ions; Curtain gas is a curtain gas that prevents neutral molecules or small droplets from entering the mass analyzer and reduces background noise; Exhaust gas is used for exhaust gas. The initial nitrogen source for liquid chromatography-mass spectrometry was mainly liquid nitrogen. Although the nitrogen produced by liquid nitrogen has a high purity, it also has disadvantages such as inability to remove hydrocarbons, containing certain amounts of water, inconvenient transportation and ventilation, and the risk of frostbite.
There are two main reasons why people initially did not choose a nitrogen generator: first, they were concerned about purity issues; second, the cost is relatively high. But with the continuous development of technology, some excellent ethnic brands have emerged in China. These enterprises do not have tariffs and agency fees when selling their products, saving more of these costs for improving product quality. In addition, they tailor their products to local conditions in response to the high humidity and dirtiness of the domestic air. From then on, the psychology of mass spectrometry users began to change with nitrogen generators. Most newly purchased mass spectrometers were directly equipped with generators, and previous mass spectrometers gradually replaced liquid nitrogen tanks with nitrogen generators. According to the scale of laboratory mass spectrometry, the corresponding configuration of nitrogen generators can be divided into integrated machines, combined machines, and split machines. However, the basic structure of the nitrogen generator is consistent, followed by an air compressor, a refrigerated dryer, a filter, an air storage tank, a nitrogen generator, and a high-purity nitrogen gas, as shown in the figure. The centralized gas supply source in the liquid laboratory mainly includes four parts. The air compressor converts low-pressure air in the air into air with a certain pressure, and the filter membrane in the compressor also plays a certain filtering role; The function of a refrigerated dryer is to remove moisture from compressed air; The function of a filter is to remove oil and dust from compressed air and deeply purify the air; The function of the air storage tank is to reduce the airflow pulse and act as a buffer. Due to the fact that the source of gas produced by the nitrogen generator is air, the efficiency and operating status of the air compressor directly affect the efficiency and quality of gas produced by the generator in the gas source system.
The selection of gas source for centralized gas supply in the liquid quality laboratory is actually the most important aspect of selecting the air compressor. Air compressors can be divided into many types according to their principles, such as piston air compressors, screw air compressors, and turbine air compressors. But for the compressors used in nitrogen generators, the most commonly used one on the market is the vortex compressor.
The principle of a vortex compressor: 1. Inhale air through the suction port on the outer side of the fixed vortex; 2. The compressed air enclosed in a compressed space is compressed towards the center due to the reduction of compressed air caused by rotational motion; 3. The compressed space becomes minimized at the center, and the air that is compressed to the maximum limit is compressed outward through the exhaust port at the center; 4. The movement of 1-3 (suction → compression → exhaust) will be repeated. After years of continuous technological innovation, the scroll compressor has the advantages of clean and oil-free, low vibration, low noise, reliable and stable operation, making great contributions to customers in environmental protection, energy conservation and emission reduction, and improving production efficiency.