GC Troubleshooting Poster
Contents
1. Increase GC oven programming rate Lower GC oven start temperature Reduce retention of compounds by decreasing film thickness and length See Carryover Ghost Peaks solutions iso 2013 Restek Corporation i 1 Allright reserved Lit Cat GNWC1723 UNV printedinthe USA2. No peaks from FID Column flow Broken column Return detector to operating condition and light flame Verify condensation is gone gases are on and column is correctly installed There is flow Syringe works and the column and contains is not broken sample f Test Check Re inject Syringe plugged or broken Sample in syringe Repair or replace syringe ensure syringe is filling Adjust flow or replace column Are there peaks SYMPTOMS AND SOLUTIONS Good chromatography is critical to obtaining accurate reproducible results Coelutions asymmetric peaks baseline noise and other issues are common challenges in the GC laboratory These an alytical problems and others can be overcome by troubleshooting your separations using the tips below Poor Resolution Causes Solutions Non selective stationary phase Poor efficiency Sample overload Incorrect analytical conditions used Choose appropriate stationary phase and column dimensions Optimize carrier gas linear velocity and GC oven temperature program Adjust sample concentration or amount on column Verify temperature program flow rates and column parameters Poor Retention Time Reproducibility Solutions Leak check injector and press fit connections Replace critical seals i e septa O rings inlet disc etc Maintain inlet liner and GC column Analyte a
3. Clean injector and detector Check for oxygen leaks across the entire system and replace seals and or filters Replace column Unstable Baseline Spiking Noise Drift Spiking Causes Carrier gas leak or contamination Injector or detector contamination Column contamination or stationary phase bleed Septum coring bleed Loose cable or circuit board connections Variable carrier gas or detector gas flows Detector not ready Solutions Leak check connections and replace seals if needed Replace carrier gas and or detector gas filters Clean system and perform regular maintenance and rinse column Replace septum Inspect inlet liner for septa particles and replace liner if needed Clean and repair electrical connections Verify flow rates are steady and reproducible may need to replace or repair flow controller Leak check system Allow enough time for detector temperatures and flows to equilibrate Response Variation Causes Sample issues Syringe problems Electronics Dirty or damaged detector Flow temperature settings wrong or variable Adsorption reactivity Leaks Change in sample introduction injection method Solutions Check sample concentration Check sample preparation procedure Check sample decomposition shelf life Replace syringe Check autosampler operation Verify signal settings and adjust if neede
4. BASIC STEPS GC Troubleshooting Tips Follow these basic troubleshooting steps to isolate problems related to the sample injector detector and column Check the obvious explanations first and change only one thing at a time until you identify and resolve the problem Check the Obvious Power supply Gas purity Electrical connections Gas flows Signal connections Identify the Cause Temperature settings Syringe condition Sample preparation Analytical conditions Define the problem clearly for example Over the last 4 days only the phenols in my sample have been tailing Review sample and maintenance records to identify trends in the data or problem indicators such as area counts decreasing over time or injector maintenance not being performed as scheduled Use a logical sequence of steps to isolate possible causes Document Work and Verify System Performance Document all troubleshooting steps and results this may help you identify and solve the next problem faster Always inject a test mix and compare to previous data to ensure restored performance EXAMPLE TROUBLESHOOTING SEQUENCE An analyst observed that no peaks appeared during a GC FID analysis The flowchart below shows a logical progression of steps that can be used to identify the cause and correct the problem Test Check Water condensation Test Check Detector gases on Column installed correctly Plugged FID jet
5. allation distances Injection 1 Injection 2 Split Peaks Causes Mismatched solvent stationary phase polarity Incomplete vaporization Sample loading capacity exceeded Fast autosampler injection into open liner Solutions Adjust solvent or stationary phase to allow wetting Add surface area such as wool to the inlet liner to enhance vaporization Use proper injector temperature Inject less sample dilute use split injection reduce injection volume Use wool or slow injection speed Carryover Ghost Peaks Causes Contaminated syringe or rinse solvent Backflash sample volume exceeds liner volume Last analysis ended too soon Solutions Replace rinse solvent Rinse or replace syringe Inject a smaller amount Use a liner with a large internal diameter Increase head pressure i e flowrate to contain the vapor cloud Use slower injection rate Lower inlet temperature Increase split flow Use liner with packing Use pressure pulse injection Extend analysis time to allow all components and or matrix interferences to elute High Bleed Causes Improper column conditioning Contamination Leak in system and oxidation of stationary phase Solutions Increase conditioning time and or temperature Trim column and or heat to maximum temperature to remove contaminants Replace carrier gas and or detector gas filters
6. d Repair or replace cables or boards Perform detector maintenance or replace parts Verify steady flow rates and temperatures then adjust settings and or replace parts if needed Remove contamination and use properly deactivated liner seal and column Check for leaks at all connections and repair connections as needed Verify injection technique and change back to original technique Check that split ratio is correct Verify that the splitless hold time is correct No Peaks Causes Injection problems Broken column Column installed into wrong injector or detector Detector problems Solutions Plugged syringe clean or replace syringe Verify there is sample in the syringe Injecting into wrong inlet reset autosampler Verify carrier gas is flowing Replace column Re install column Signal not recorded check detector cables and verify that detector is turned on Detector gas turned off or wrong flow rates used turn detector on and or adjust flow rates Broad Peaks Causes High dead volume Low flow rates Slow GC oven program Poor analyte solvent focusing Column film is too thick Sample carryover Solutions Minimize dead volume in the GC system verify proper column installation proper connectors proper liners etc Verify injector and detector flow rates and adjust if needed Verify make up gas flow and adjust if needed
7. dsorption Resolution integration issues Incorrect column oven temperature program Incorrect or variable carrier gas flow rate linear velocity Poor control of oven temperature programming Incorrect oven equilibration If manual injection delay between pushing start and actual injection Use properly deactivated liners seals and columns Avoid sample overload Verify column temperature and oven temperature program Verify the carrier gas flow and linear velocity Repair or replace parts if neccessary Confirm GC oven program falls within instrument manufacturer s recommendation Extend GC oven equilibration time Use autosampler or standardize manual injection procedure Fronting Peaks Causes Solutions Incompatible stationary phase Column overloading Choose appropriate stationary phase Reduce amount injected dilute sample Increase column inner diameter and or film thickness Tailing Peaks Causes Solutions Adsorption due to surface activity or contamination properly cleaned and deactivated liner seal and column Trim inlet end of column Replace column if damaged Adsorption due to chemical Leak in system Derivatize compound Check for leaks at all connections replace critical seals if needed Minimize dead volume Installation issues Verify that the column is cut properly square Verify correct inst
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