GC Troubleshooting Tips BASIC STEPS SYMPTOMS AND SOLUTIONS 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. 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 analytical problems and others can be overcome by troubleshooting your separations using the tips below. Check the Obvious: • Power supply • Electrical connections • Signal connections • Gas purity • Gas flows • Temperature settings • Syringe condition • Sample preparation • Analytical conditions Split Peaks Causes Solutions Causes Mismatched solvent/stationary phase polarity • Adjust solvent or stationary phase to allow wetting. Sample issues Incomplete vaporization Identify the Cause: Causes Solutions • Define the problem clearly; for example, “Over the last 4 days, only the phenols in my sample have been tailing.” Non-selective stationary phase • Choose appropriate stationary phase and column dimensions. • 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. Poor efficiency • Optimize carrier gas linear velocity and GC oven temperature program. • Use a logical sequence of steps to isolate possible causes. Sample overload • Adjust sample concentration or amount on column. Incorrect analytical conditions used • Verify temperature program, flow rates, and column parameters. Document Work and Verify System Performance: • Document all troubleshooting steps and results; this may help you identify and solve the next problem faster. Sample loading capacity exceeded Carryover/Ghost Peaks Causes Solutions Contaminated syringe or rinse solvent • Replace rinse solvent. Is the flame lit? No peaks from FID Test/Check: • Water condensation? • Detector gases on? • Column installed correctly? • Plugged FID jet? Causes Leaks • Replace critical seals (i.e., septa, O-rings, inlet disc, etc.) NO Return detector to operating condition and light flame. Verify condensation is gone, gases are on, and column is correctly installed. Analyte adsorption END YES Test/Check: • Syringe plugged or broken? • Sample in syringe? NO Re-inject NO Adjust flow or replace column. Syringe problems • Replace syringe. • Check autosampler operation. • Verify signal settings and adjust if needed. Electronics • Repair or replace cables or boards. Dirty or damaged detector • Perform detector maintenance or replace parts. Adsorption/reactivity • Remove contamination and use properly deactivated liner, seal, and column. Leaks • Check for leaks at all connections and repair connections as needed. Change in sample introduction/injection method • Verify injection technique and change back to original technique. • Check that split ratio is correct. • Verify that the splitless hold time is correct. Repair or replace syringe; ensure syringe is filling. Are there peaks? No Peaks • Increase split flow. • Use liner with packing. Injection 2 • Use pressure-pulse injection. Last analysis ended too soon • Use properly deactivated liners, seals, and columns. • Extend analysis time to allow all components and/or matrix interferences to elute. Solutions Causes Injection problems • Plugged syringe; clean or replace syringe. • Verify there is sample in the syringe. • Injecting into wrong inlet; reset autosampler. • Verify carrier gas is flowing. Resolution/integration issues • Avoid sample overload. Broken column • Replace column. Incorrect column/oven temperature program • Verify column temperature and oven temperature program. Column installed into wrong injector or detector • Re-install column. High Bleed Incorrect or variable carrier • Verify the carrier gas flow and linear velocity. gas flow rate/linear velocity Repair or replace parts if neccessary. Poor control of oven • Confirm GC oven program falls within temperature programming instrument manufacturer’s recommendation. Incorrect oven equilibration time • Extend GC oven equilibration time. If manual injection, delay between pushing start and actual injection • Use autosampler or standardize manual injection procedure. Causes Solutions Improper column conditioning • Increase conditioning time and/or temperature. Contamination Solutions Incompatible stationary phase • Choose appropriate stationary phase. Column overloading • Increase column inner diameter and/or film thickness. • Replace column. Spiking Carrier gas leak or contamination Adsorption due to surface activity or contamination • Use properly cleaned and deactivated liner, seal, and column. Leak in system • Download our Guide to GC Column Selection and Optimizing Separations (lit. cat.# GNBR1724- UNV) Installation issues • Check for leaks at all connections, replace critical seals if needed. High dead volume Low flow rates • Verify injector and detector flow rates and adjust if needed. Slow GC oven program • Increase GC oven programming rate. • Replace carrier gas and/or detector gas filters. Poor analyte/solvent focusing • Lower GC oven start temperature. • Clean system and perform regular maintenance. Column film is too thick • Reduce retention of compounds by decreasing film thickness and length. Sample carryover • See Carryover/Ghost Peaks solutions. • Leak check connections and replace seals if needed. Septum coring/bleed • Inspect inlet liner for septa particles and replace liner if needed. Loose cable or circuit board connections • Clean and repair electrical connections. Noise • Replace column if damaged. For an in-depth discussion on how to choose the right column and improve your chromatographic results, visit www.restek.com Solutions • Minimize dead volume in the GC system; verify proper column installation, proper connectors, proper liners, etc. • Replace septum. • Trim inlet end of column. Adsorption due to chemical • Derivatize compound. composition of compound Solutions • Condition, trim, and rinse column. Column contamination or stationary phase bleed Tailing Peaks Solutions Causes • Verify make-up gas flow and adjust if needed. Injector or detector contamination Causes Broad Peaks • Check for oxygen leaks across the entire system and replace seals and/or filters. Unstable Baseline (Spiking, Noise, Drift) Causes • Reduce amount injected, dilute sample. • Detector gas turned off or wrong flow rates used; turn detector on and/or adjust flow rates. • Replace carrier gas and/or detector gas filters. • Clean injector and detector. Leak in system and oxidation of stationary phase Causes Detector problems • Signal not recorded; check detector cables and verify that detector is turned on. • Trim column and/or heat to maximum temperature to remove contaminants. Fronting Peaks • Request our Simplifying Column Selection poster (GNWC1612-UNV) • Check sample decomposition/shelf life. Backflash (sample volume • Use slower injection rate. exceeds liner volume) • Lower inlet temperature. Solutions • Leak check injector and press-fit connections. Is the sample reaching the column? Test/Check: • Column flow? • Broken column? • Check sample preparation procedure. • Increase head pressure (i.e., flowrate) to contain the vapor cloud. Poor Retention Time Reproducibility Syringe works and contains sample. YES Is there adequate column flow? • Check sample concentration. • Use a liner with a large internal diameter. • Maintain inlet liner and GC column. YES • Rinse or replace syringe. • Inject a smaller amount. 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. YES Solutions • Verify steady flow rates and temperatures, then Flow/temperature settings wrong or variable adjust settings and/or replace parts if needed. Injection 1 EXAMPLE TROUBLESHOOTING SEQUENCE Flame is lit. • Inject less sample (dilute, use split injection, reduce injection volume). Fast autosampler injection • Use wool or slow injection speed. into open liner • Always inject a test mix and compare to previous data to ensure restored performance. There is flow and the column is not broken. • Add surface area, such as wool, to the inlet liner to enhance vaporization. • Use proper injector temperature. Poor Resolution Response Variation Drift Variable carrier gas or detector gas flows Detector not ready • 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. • Minimize dead volume. • Verify that the column is cut properly (square). • Verify correct installation distances. Lit. Cat.# GNWC1723-UNV © 2013 Restek Corporation. All rights reserved. Printed in the U.S.A.