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Excessive Background Noise in GC

Created by Agilent Knowledge Portal Agilent Knowledge Portal 8 months ago | Last modified by Carlos Vargas Carlos Vargas 7 months ago

This Information Applies To: Agilent GC Systems


Issue

Excessive baseline noise can be introduced at different points including sample preparation, sample introduction, separation, and the detector. The excessive background can cause reduced signal-to-noise (detection limit), creating inaccurate quantitative or qualitative results. 

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

Over time sample deposits can accumulate in the analytical pathway and slowly leach out during subsequent sample analyses (Figure 1). The background can be consistently high across the entire sample run, or vary with the temperature program, and can vary significantly when the instrument is run continuously and after sitting idle. 


Figure 1. Excessive background noise
1. Normal background with peaks visible, 2. Excessive background with peaks partially obscured

Resolution

 Possible sources of ghost peaks and carry over include:

  1. Sample preparation

    Background noise from the sample can be present during the run due to sample preparation:

    Possible source of background noise Solution
    Low quality or contaminated solvent Check to see if the problems coincided with a change in solvent supply. If they did, change to a known contamination free solvent supply
    Matrix effects from sample  Sample or extract clean up before the analysis
    Sample contaminated during preparation (including contamination of solvent) Check sample handling steps. Repeat sample preparation as necessary

  2. Sample introduction system 

    Perform the GC Condensation Test to determine if the sample introduction system is the source of the contamination.

    Possible source of contamination Solution
    Low quality or contaminated gas supply Check to see if the problems coincided with a change in gas cylinder. If they did, change the gas cylinder and flush the gas lines for sufficient time to clear the volume of the gas system
    Contaminated gas filter Check the gas filter indicator (if available). If not, replace as per the maintenance schedule or after using contaminated gas
    Septum bleed or degradation Replace the septum. Use an Agilent high-quality septum appropriate for your inlet temperature. See Replacing the Inlet Septum for Split/Spitless and Multimode Inlets 
    Inlet liner dirty Replace the inlet liner. Use an Agilent inlet liner appropriate for your injection volume, solvent, and injection mode
    Gold seal is dirty Replace the gold seal. See How to replace the Gold Seal on the Split/Splitless (SSL) Inlet for an Agilent GC 
    Inlet is contaminated Clean or bake out the inlet. See How to Bake-out the Split/Splitless Inlet (SSL) on Agilent GC Systems 

  3. Analytical column 

    Possible source of contamination Solution
    Column contamination Bake out the column. Limit the bake-out for 1 to 2 hours
     Caution 
    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
    Column inserted too far/not far enough into the detector Remove and reinstall the column. See Capillary Column Installation Quick Reference Guide 
     
  4. Detector

    Possible source of contamination Solution
    Detector contamination Typically detector contamination increases over time and not suddenly. Clean the detector
    Incorrect detector flow rates Check that the flow rates are within recommended specifications
    Detector leak (for MS, ECD, TCD) Leak test the detector
    Old detector filament, lamp, electron multiplier, or ion source Review instrument logs. Clean or replace affected components

 If these procedures have not resolved the excessive baseline noise, contact Agilent Technical Support.

 Tip 
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
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