Jo Boden
Carlos VargasThis Information Applies To: Agilent GC Systems
Issue
A change in peak size can occur for single, multiple or all peaks.
Other chromatographic problems are identified in Basic Troubleshooting for GC Systems . Regular maintenance of your instrument in accordance with the recommended maintenance schedule will reduce the incidence of chromatography problems.
Background
Changes in peak size can be the result of changes analytical conditions, sample concentration, or injector problems (Figure 1):
Figure 1. Change in peak size
1. Some peaks change size, 2. All peaks change size
| Possible cause of change in peak size | Solution | ||
| Coelution | Improve separation of peaks, or clean up the sample | ||
| Change in sample concentration | Check if new standards have been recently prepared. Changes may be caused by preparation error, degradation, evaporation, or variances in sample temperature or pH | ||
| Blocked or partially blocked syringe | Check that the syringe plunger is moving freely. The solution should be pulled into the syringe body, and moving freely and fast when plunger is depressed | ||
| Leak in the syringe | Replace the syringe. Leaks can occur around the plunger or around the needle; leaks are often not readily visible | ||
| Septum leak | Replace the septum | ||
| Injector leak | Leak check the injector: How to Run and Interpret the Inlet Leak and Restriction Test for the Agilent 7890/8860/8890 GC Systems | ||
| Inlet contamination causing compound degradation | Replace the inlet liner, gold seal, bake out inlet Split/Splitless Inlet Bakeout Procedure | ||
| Column contamination | Bake out the column. Limit the bake-out for 1 to2 hours
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| Column activity (active compounds) | Irreversible. Replace the column | ||
| Change in injector discrimination (most severe for split injections) | Check injector parameters | ||
| Inlet overload (vapor volume too large for installed inlet liner) | Use Agilent Vapor Volume Calculator to adjust injection size, liner volume, inlet temperature, or solvent. Less injection volume and higher flow rates are helpful | ||
| Change in detector response (some or all peaks, and background) | Check gas flows, temperatures, and settings | ||
| Change in background level or noise (peak area) | See Excessive Background Noise in GC and Baseline Instability in GC | ||
| Change in the method settings | Check injection volume, purge activation time (splitless only), split ratio, septum purge flow, carrier gas flow, column temperature | ||
| Sample solvent incompatibility (splitless injections) | Change the sample solvent or use a retention gap |
If these procedures have not resolved the change in peak size problems, contact Agilent Technical Support.
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Learn how to effectively troubleshoot your Agilent GC System:
GC-0GEN-1040z - Practical Steps in GC Troubleshooting
GC-0GEN-2040zs - GC Troubleshooting Series e-learning courses available from Agilent education |
