1. What is so important about GC calibration?
GC calibration is the process of adjusting the instrument to ensure accurate and reliable quantitative analysis results. It involves analyzing a known standard mixture to create a calibration curve, which is used to determine the concentration of an unknown sample. Proper calibration ensures measurement accuracy, instrument consistency, and compliance with regulatory standards (e.g., EPA, ISO).
2. What types of calibration methods are used in GC?
The two most common calibration methods are:
- External standard calibration: Standard solutions are run separately from the sample. This method is simple but sensitive to changes in injection volume.
- Internal standard calibration: A known amount of an internal standard is added to the sample and calibration standard. This method can compensate for differences in injection volume and detectors and is widely used in quantitative GC analysis.
3. What types of standards are used for GC calibration?
The calibration standard solution should meet the following requirements:
- Chemically similar to the target analyte
- Have a known and traceable concentration
4. How to perform a basic GC calibration step by step?
Here is a simplified GC calibration workflow:
- Prepare calibration standards at multiple concentration levels (at least 3-5 points)
- Warm up the instrument and stabilize flow, temperature, and detector settings
- Inject each standard and record the response (peak area or peak height)
- Plot a calibration curve (concentration vs. response)
- Perform linear regression to generate the calibration equation
- Inject unknown samples and calculate their concentration using the equation
5. What are common calibration problems? How to solve them?
Here are some typical calibration problems and their solutions:
- Poor linearity (R² < 0.99) → Use new standards and check injection consistency
- Peak area fluctuations → Stabilize pressure and injector temperature
- Baseline drift → Clean detector or check carrier gas purity
- No peaks or ghost peaks → Check column, inlet, or leaks