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  • Category :  Agilent Knowledge Portal
  • Entry Type :  Article
  • Product Type :  GC Sample Preparation and Introduction GC Systems
  • Component :  Automatic Liquid Samplers GC Inlets GC System PAL Autosampler Systems
  • Product Name :  6850 Automatic Liquid Sampler 6850 GC System 6890 GC System 7650A Automatic Liquid Sampler 7683 Automatic Liquid Sampler 7693A Automatic Liquid Sampler 7820 GC System 7890 GC System 8860 GC System 8890 GC System Intuvo 9000 GC System PAL 3 CTC Autosampler System PAL XT CTC Autosampler System
  • Task :  Troubleshooting
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Peak Retention Time Shift in GC

Answer

This Information Applies To: Agilent GC Systems

Issue

A shift in retention time 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

Retention time (RT) shifts can be the result of changes analytical conditions, sample concentrations, column, or injector problems (Figure 1):

          
Figure 1. Retention time shift
1. Normal retention time, 2. Retention time increased (all analytes)

Possible cause of retention time shift Solution
Overloading from a large change in analyte concentration Dilute the sample
Septum leak Replace the septum
Injection technique 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. Use an autosampler
Leak in the injector Leak check the injector How to Run and Interpret the Inlet Leak and Restriction Test for the Agilent 7890/8860/8890 GC Systems 
Change in carrier gas flow rate (all peaks similar RT shift) Check the carrier gas flow rate. Carrier gas flow rate can be measured with an unretained compound
Sample solvent incompatibility (splitless injections) Change the sample solvent or use a retention gap
Change in column temperature Check any changes in the method column temperature
Change in column dimension 

Verify that the installed column matches the configured column in the instrument and the method column.
Changes in column dimension impact carrier gas flow rate, a common cause is multiple trimming over the column lifetime
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 


If these procedures have not resolved the retention time shift problem, contact Agilent Technical Support.

 Tip 
Learn how to effectively troubleshoot your Agilent GC System:
 
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