Peak Size Changes in GC

This 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    Caution: Do not exceed the manufacturer recommended maximum column temperate limit as it will damage your column. Trim the column: Remove 0.5 to 1 m from the front of the column. Trimming the column many times over its lifetime will change the effective column length, and impact retention times. Adjust instrument set column length every time the column is trimmed
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.

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