Gas Chromatography-Mass Spectrometry (GC-MS) is a commonly used analytical technique that combines the methods of Gas Chromatography (GC) and Mass Spectrometry (MS). This technique can separate the compounds in a sample and then perform mass spectrometry analysis on each compound after separation. Due to the combination of GC’s high separation efficiency and MS’s high sensitivity and qualitative analysis capability, it is widely used in fields such as chemistry, biochemistry, and pharmacy, especially for the analysis and qualitative and quantitative analysis of complex mixtures.
Medicilon Cloud Lecture Hall invites Senior Group Leader of the Process Department, Ting Li, to explore the possibilities of GC-MS technology with you, drawing on her years of practical experience, and to answer any questions and concerns that may arise during operation.
Q1. When does GC-MS need to be tuned?
Ting Li: Tuning is required after shutting down and restarting the system. Additionally, if any hardware maintenance is performed during the use of the equipment, tuning is also necessary. Moreover, tuning is needed if the following issues are encountered during actual testing:
Sensitivity Reduction: If a sudden and significant drop in sensitivity is detected
Method Reproducibility Issues: If a previously successful method can no longer be reproduced
Target Ion Missing: If the expected target ion cannot be detected
In these cases, tuning is needed to check whether the issues are caused by factors such as ion source contamination or mass axis shift.
Analytical Testing Center
Q2. If the sample solubility is not very good and setting the split ratio to 1:1 meets the requirements for improving the response of the target compound, is it still necessary to set the split ratio?
Ting Li: Regarding the appropriateness of the split ratio, it should be noted that not all smaller split ratios are unreasonable. However, it is important to keep in mind that if the split ratio is too small, it will result in a corresponding decrease in the split flow rate. In this case, the ratio valve may not be able to precisely control the flow rate, which can affect the accuracy and precision of the analysis. Specifically, when the split ratio is below 5:1, we recommend using a non-split injection to avoid reduced control precision caused by the low split ratio, which could impact the reliability of the analysis results.
Q3. Can water be used as a diluent for headspace injection in GC-MS?
Ting Li: In the discussion during the live broadcast, it was mentioned that using water as a diluent should be avoided when performing direct injection. However, headspace injection is a viable option. The principle of headspace injection is to place the sample solution in a headspace vial and heat it to allow volatile components to escape from the sample, reaching a gas-liquid equilibrium.
This method involves analyzing the gas extracted from the top of the headspace vial. Since water has a low vapor pressure and is not easily volatilized, its concentration at the top of the headspace vial is relatively low. This means that when using headspace analysis, the amount of water entering the system is minimal. This helps reduce the interference of water on the analytical results, thereby improving the accuracy of the analysis.
Q4. When quantifying multiple ions, should the spectra be processed by integrating under each specific ion rather than under the total ion current?
Ting Li: When performing quantitative analysis of multiple ions, we should pay attention to the method of spectrum processing. Theoretically, we should integrate each quantitative ion individually rather than under the total ion current. Doing so can help avoid interference from other ions in our analysis results. Our team has also confirmed with engineers that if only one compound is being analyzed, qualitative ions can indeed be included in the quantitative analysis. This is similar to using the total ion current spectrum for calculations in Selected Ion Monitoring (SIM) mode. This approach can offer a more comprehensive analysis in specific situations.
In summary, we should choose the appropriate spectrum processing method based on the specific analysis requirements and the characteristics of the target compounds. If the goal is precise quantification of multiple ions, each ion should be extracted and integrated separately. If the goal is to analyze a single compound and qualitative ion information is needed, you can consider incorporating qualitative ions into the quantitative analysis.
Whether you are a senior expert in the pharmaceutical industry or a curious newcomer to cutting-edge medical technologies, Medicilon Cloud Lectures Hall will open a door to the future of drug development for you. If you have popular topics you’re interested in or if you’re curious about preclinical research services and would like a detailed introduction in the Cloud Lectures Hall, please feel free to leave a message or ask questions.
