High pressure injection systems are commonly used in analytical instruments such as liquid chromatography (HPLC) and gas chromatography (GC) to accurately inject liquid or gas samples into chromatography columns or analytical instruments under high pressure. The core purpose of this system is to transport the sample to the analysis system at a stable flow rate under high pressure environment to ensure accurate separation and detection. The following is the principle and operation method of the high-pressure injection system:
1. Principle of High Pressure Sampling System
1.1 Sample injector function
The function of a high-pressure injector is to accurately inject external samples into the chromatographic column under high-pressure conditions through the system pipeline, ensuring the controllability of parameters such as sample volume, flow rate, and injection time. The injector usually consists of the following parts:
Injection valve: Used for precise control of the sample injection volume. Common injection valves include six way valves, ten way valves, etc.
Injection port/injection needle: Connect an external sample source and inject the sample into the system through a valve.
Pressure source (pump): responsible for maintaining high pressure in the system so that the sample can be injected into the chromatographic column.
1.2 High pressure injection
The working principle of high-pressure injection system is based on the method of injecting liquid into the system under high-pressure environment. In liquid chromatography, the high pressure generated by the pump causes the sample to enter the chromatography column through the injection valve. When liquid samples are injected, they are quickly injected through a small hole, and the injection pressure is usually between 100-400 bar. Due to the rapid injection of the sample, it will quickly mix with the mobile phase and enter the chromatographic column for separation.
1.3 Allocation and Flow Control
The high-pressure injection system relies on precise control of the pump to maintain stable injection flow rate. Usually, the pump is linked with the injection valve to ensure that the sample enters the chromatographic column at the appropriate flow rate, thereby avoiding any possible decrease in separation efficiency.
2. Components of high-pressure injection system
2.1 Syringe
Used to extract a certain volume of sample and accurately inject it into the system. The volume of the sample is usually very small, and microinjection is a common practice.
2.2 Injection valve
Usually, it is a six way or ten way valve to ensure that the sample can be injected into the chromatographic column at the appropriate time. When the valve is opened, the syringe injects the sample into the chromatography system; When the valve is closed, the mobile phase of the chromatographic column continues to flow without interference.
2.3注射口
The injection port is the interface between the syringe and the chromatographic system, usually designed with high sealing to prevent sample leakage.
2.4 Pump system
Mainly used to provide the required high-pressure fluid for the system, the pump can maintain a certain pressure and flow rate to ensure stable sample entry into the chromatographic column.
3. Operation method of high-pressure injection system
3.1 Preparation work
Before operating the high-pressure injection system, a series of preparatory work is required:
Check the instrument: Ensure that the instrument is in normal working condition, and that there are no blockages in the pump, valves, and pipelines.
Prepare samples: Prepare samples according to requirements to ensure that the sample concentration is suitable for experimental needs. If necessary, use a filter to remove particulate matter from the sample.
Set parameters: Set the flow rate, injection volume, pressure, and other parameters of the pump according to the analysis requirements.
3.2 Injection samples
Loading samples: Load the samples into the syringe, taking care to avoid air bubbles and contamination.
Operation of injection valve: Manually or through software control of the injection valve, inject the sample into the chromatographic column. At this point, the valve will rotate, opening a channel for the sample to flow into the analysis system.
Start the pump: Start the pump, maintain high pressure, control the flow rate of the mobile phase, and ensure that the sample can enter the chromatographic column according to the preset time.
3.3 High pressure injection
Perform high-pressure injection: According to the settings, the pump will provide the required high pressure to inject the sample into the chromatographic column. At this point, the injection valve starts working and the sample is quickly injected into the system for analysis.
Injection completion: Once the injection is completed, the injection valve will automatically close, stopping the sample injection. At this point, the pump will continue to maintain the flow of the mobile phase.
3.4 Testing and Data Recording
After the sample enters the chromatographic column, separation begins. Detectors (such as UV detectors, light scattering detectors, etc.) will monitor changes in sample composition in real time and record data. Various information during the separation process, such as chromatographic peaks, can be viewed through a computer control system.
3.5 Cleaning and maintenance after operation
Clean injection valve and pipeline: After each use, clean the injection valve and pipeline to prevent sample residue from affecting the next measurement.
Check the pump and system pressure: Regularly check the pressure system of the pump to ensure its stability.
Calibration instrument: Regularly calibrate the high-pressure injection system to ensure its measurement accuracy.
4. Precautions
4.1 Injection volume control
Accurately controlling the injection volume is very important. Excessive injection volume may cause overload of the chromatographic column, while insufficient injection volume may result in insufficient signal strength.
4.2 Preventing Bubbles
During the injection process, it is important to avoid air bubbles from entering the system. Bubbles can cause pressure fluctuations in the system, thereby affecting measurement results.
4.3 Pressure Monitoring
The pressure setting of the high-pressure injection system is crucial, as excessively high or low pressure can lead to sample loss, equipment damage, or analysis result errors.
4.4 Regular maintenance
Regularly inspect and clean components such as injection valves, syringes, pumps, etc. to extend equipment life and improve analysis accuracy.
5. Summary
High pressure injection systems play an important role in modern analytical instruments. Through precise sample injection and high-pressure delivery techniques, liquid samples can be effectively introduced into the analysis system, achieving efficient separation and detection. During operation, it is necessary to strictly control the injection volume, pressure, and flow rate to ensure the stable entry of the sample and the normal operation of the system. Regular cleaning and maintenance are also key to ensuring the long-term stable operation of the instrument.