Gas Chromatography (GC) is an efficient physical separation technique based on the principle of separating different substances in a chromatographic column through the flow of a carrier gas. The advantages of gas chromatography make it frequently used in quality research, making it an indispensable technique in modern pharmaceutical analysis.
High Resolution: Capable of precisely separating various compounds in complex mixtures into individual components
Ultra-High Sensitivity: Capable of detecting trace amounts of target compounds in samples, providing a powerful tool for trace analysis
- Rapid Analysis: Detection typically takes just a few minutes to several tens of minutes, significantly improving analytical efficiency
High Throughput: Suitable for batch sample processing, capable of analyzing a large number of samples in a short period, meeting the high-efficiency demands of research and development
The Cloud Lecture Hall invites Yameng He from Medicilon’s Process Department to present the unique advantages and powerful capabilities of gas chromatography in the field of pharmaceutical analysis. Yameng He will also address any confusion you might have encountered during experiments and provide strategies to overcome these challenges.
01. How should the aging program be set appropriately?
Yameng He: When aging column, it is recommended to follow these steps: first, under low-temperature conditions (e.g., 40°C), purge the column with carrier gas for 15 minutes to blow away the residual oxygen. Then, gradually increase the temperature at a rate of 5 to 10°C per minute until reaching a temperature that the column can withstand, which should be 20°C lower than the column’s maximum allowable temperature. After reaching the target temperature, hold for 30 to 40 minutes to ensure the stability of the column. It is recommended to repeat this process 2 to 3 times to effectively extend the lifespan of the column.
Analytical Testing Center
02. What could be the cause of small spikes often appearing during baseline monitoring?
Yameng He: First, you need to confirm the direction of the spikes; whether they are positive, negative, or both. If spikes are present in both directions, it may be related to the electrical environment. If the spikes are only in one direction, they may originate from trace solid particles in the gas lines, column or detector, and each component should be checked step by step.
03. If peaks that were previously separable suddenly cannot be separated during detection, how should you age the chromatographic column in this situation?
Yameng He: First, you need to confirm whether the column you are using has good separation performance. If peaks that were previously successfully separated are now not separating, first confirm whether the column is a high-efficiency column. If it is, the column may have developed issues. It is recommended to cut a portion from the head of the column and then process it using the aging program.
04. How should the carrier gas be selected?
Yameng He: The carrier gas should have good chemical stability and high purity. Commonly used carrier gases include hydrogen, helium, argon, and nitrogen. Hydrogen has characteristics such as a relatively small molecular weight, high thermal conductivity, and low viscosity, making it a common carrier gas for thermal conductivity detectors and an essential fuel gas for hydrogen flame ionization detectors. However, hydrogen is highly flammable and explosive, so special safety precautions should be taken when using it.
Helium has a relatively small molecular weight, high thermal conductivity, low viscosity, and allows for higher linear velocities during use. Compared to hydrogen, it is safer but more expensive, and is commonly used in gas chromatography-mass spectrometry (GC-MS) analysis. Argon has a relatively large molecular weight and low thermal conductivity, but due to its high cost, it is used less frequently. Nitrogen has a relatively large molecular weight, small diffusion coefficient, high column efficiency, is safe, and is inexpensive. It is commonly used as the carrier gas for hydrogen flame ionization detectors.
05. When measuring moisture with a TCD detector, can the diluent introduce moisture, and how can it be avoided?
Yameng He: Diluent can introduce moisture, affecting the detection results. To avoid this, you can use anhydrous diluents or remove moisture from the diluent using molecular sieves.
06. When selecting a gas chromatography column, how should the inner diameter of the column be chosen?
Yameng He:
- For higher column efficiency, a column with an inner diameter of 0.18 to 0.25 mm can be used. A 0.18 mm diameter column is particularly suitable for GC/MS systems with lower pump capacity. Columns with smaller diameters have minimal capacity and require the highest column head pressure.
- For larger sample capacities, a column with an inner diameter of 0.32 mm can be used. Compared to a 0.25 mm diameter column, this type of column typically provides better separation of solutes that elute earlier when using non-split injection or large-volume (>2 µl) injections.
- Columns with a 0.45 mm inner diameter should only be used when the instrument is equipped with a large-bore direct injector and high column efficiency is required. These columns are particularly suitable for applications with high carrier gas flow rates, such as purge-and-trap, headspace sampling, and valve injection applications.
- Columns with a 0.53 mm inner diameter should only be used when equipped with a large-bore direct injector. They are particularly suitable for conditions with high carrier gas flow rates, such as purge-and-trap and headspace sampling. Columns with a 0.53 mm inner diameter offer the highest sample capacity with constant film thickness.
