Don’t Get Carried Away by Carryover: Troubleshooting GC Chromatography

Significance of the topic

Gas chromatography (GC) carryover and related artefacts compromise analytical accuracy, repeatability, and instrument uptime. In modern industrial and research laboratories, unresolved carryover can lead to false positives, lost samples, extended maintenance intervals, and increased operational costs. Addressing carryover systematically enhances method robustness, improves sensitivity for late-eluting compounds, and reduces unplanned downtime.

Objectives and study overview

This application note by Agilent Technologies presents a structured troubleshooting workflow for GC carryover. It aims to:

• Identify the root causes of extra peaks and baseline disturbances.
• Demonstrate the impact of column selections and temperature programming on carryover.
• Outline preventive and corrective measures ranging from injector maintenance to advanced backflush techniques.

Methodology and instrumentation

The approach integrates standard GC/FID and GC/MS configurations with both polar and mid-polar columns. Key elements include:

• Test mixes containing hydrocarbons, alcohols, FAMEs, acids, and bases to assess column efficiency and activity.
• Column selection: J&W DB-HeavyWAX (high maximum allowable operating temperature, low bleed) and DB-624 columns for comparative studies.
• Instrumental tools: autosampler wash protocols, diffusion-cap vials, headspace sampling parameters, and split/splitless inlets.
• Troubleshooting tests: noninjection bleed profiles, blank runs, condensation tests, and jumper tube isolations.

Used instrumentation

• Agilent 7890/8890 GC systems with split/splitless inlet and autosampler
• Flame ionization detector (FID) at 300–320 °C
• MS detector for total ion chromatograms
• Columns: J&W DB-HeavyWAX (30 m × 0.25 mm × 0.25 µm), DB-624 (30 m × 0.53 mm × 3.0 µm), guard/gap columns
• Carrier gases: Helium at 40 cm/s or Hydrogen at 37 cm/s
• Sample preparation: QuEChERS, Captiva EMR-Lipid, SPE cartridges, SPME fibers
• Backflush accessories and pressure-pulse control

Main results and discussion

1. Temperature Programming and Column Performance

• Raising final oven temperature from 250 °C to 280 °C advanced heavy-compound elution, reduced carryover peaks, and sharpened late-eluting signals.
• DB-HeavyWAX demonstrated stable retention times, low bleed over 100 h at 280 °C, and consistent peak order compared to competitive WAX phases.

2. Sample Carryover and Inlet Management

• Matrix and septum contaminations produce siloxane repeat peaks identifiable by characteristic ions at m/z 73, 147, 207.
• Autosampler wash protocols (four pre- and post-washes with compatible solvents) and diffusion-cap vials dramatically cut syringe carryover.
• Headspace sampler loop purge flow/time adjustments prevent condensation and loop-trapped vapors.

3. Advanced Backflush Techniques

• Implementing a 2–7 min backflush at 280 °C (50 psi) eliminated heavy-boiler buildup, shortened cycle times by >30 min, and stabilized retention over 10 consecutive injections.
• Comparison of blanks: without backflush exhibited persistent late peaks; with backflush produced clean baselines.

4. Troubleshooting Workflow

• Track system changes (column cuts, septum replacements).
• Isolate system components using bleed profiles, noninjection blanks, condensation tests, and jumper tube isolations to pinpoint injector, column, detector or gas issues.

Benefits and practical applications

• Enhanced sensitivity and signal-to-noise for semivolatile and high-boiling analytes.
• Reduced method development and validation time through predictable retention and low bleed.
• Lower maintenance frequency and column replacement costs via backflush and proper wash protocols.
• Broad applicability across routine QA/QC, environmental, food-flavor, forensic, and petrochemical analyses.

Future trends and potential applications

• Integration of real-time diagnostics and AI-driven troubleshooting in GC control software.
• Advanced column chemistries tailored for ultra-heavy matrices and extended temperature ranges.
• Automated high-throughput sample cleanup modules (online SPE, EMR-Lipid) coupled with backflush hardware.
• Expanding multidimensional GC×GC workflows with inline carryover suppression and rapid bake-out cycles.

Conclusion

A systematic approach to GC carryover—combining proper inlet maintenance, optimized temperature programs, rigorous wash protocols, and backflush techniques—delivers cleaner baselines, stable retention, and increased throughput. By isolating root causes and applying targeted remedies, laboratories can achieve robust, high-confidence analyses for a wide range of compounds.

Reference

Alexander Ucci; Don’t Get Carried Away by Carryover: Troubleshooting GC Chromatography; Agilent Technologies Application Note 5991-9078EN; March 20, 2024.