Basics of Gas Chromatography

4-1 Distorted peak shapes

Analytical problems can be caused by factors other than instrument failure, such as errors in the column-handling methods and inappropriate analysis conditions. The following troubleshooting guide summarizes the common problems occurring in GC analysis (mainly when using capillary columns) and their possible solution methods. The two major problem categories are peak-shape-related problems and baseline-related problems, which should be tackled based on the chromatogram information obtained by the analysis. The troubleshooting guide also provides a reference checklist for the daily inspections of column performance, which can prevent problems before they occur.

9 points were indicated: tailing, leading, peak splitting, retention time shift, peak undetected, overall small peak, Poor repeatability, ghost peak carryover, and deterioration of column performance.

Tailing

Main Causes	Approach
Column disconnection failure Improper column attachment position to inlet and detector	Cut the column tip vertically with a dedicated column cutter (see Handling Capillary Columns). Check the column insertion length. The cut position should match that specified in the instruction manual of the employed device.
Liner contamination or deterioration	Clean or replace the liner. Depending on the specimen, consider selecting a liner with or without wool or changing the wool material.
Contamination of column (liquid phase)	Conditioning of columns. Cut 50 cm off the inlet side of the column.
Small split ratio	Increase the split ratio.
Incompatibility between column (liquid phase) and solvent	Change column (liquid phase) or solvent to match polarity. Use a retention gap (see capillary column-handling instructions).
Incompatibility between column (liquid phase) and sample	When targeting highly polar components, select a liquid phase with high polarity (see How to Select a Capillary Column).
Degradation of column (liquid phase)	Replace the column.

Fronting

Main Causes	Approach
Sample load of column (liquid phase) is exceeded	Adjust the introduction volume by reducing the injection volume, increasing the split ratio, or some similar action that reduces the load to below the sample loading of the column (liquid phase). Change to a column with a thicker membrane and increase the column (liquid phase) sample load.
Incompatible polarities of column (liquid phase) and sample	Select a column (liquid phase) that matches the polarity of the analyte.

Split peaks

Main Causes	Approach
Inappropriate injection conditions	Manual injection incurs a risk of improper injection speed or a faulty syringe. Change syringes or use an autosampler.
Improper column attachment position to the inlet	Adjust the column insertion length to match the position specified in the instruction manual of the GC system.
Solvent (sample) is a mixed solvent	May occur with splitless or on-column injections. Change to a single solvent.
Column (liquid phase) and solvent (sample) are incompatible	Change the column (liquid phase) or solvent to match the polarity. Use a retention gap (see Sample Injection Methods).

Retention time shifts

Main Causes	Approach
Carrier gas leakage	Check for leaks, mainly around the inlet and at the column connection. If the inlet septum is leaking, replace the septum.
Column (liquid phase) and solvent (sample) are incompatible	Change column (liquid phase) or solvent to match the polarity. Use a retention gap (see Sample Injection Methods).
Degradation of column (liquid phase)	Replace the column.
Clogged piping, flow regulator failure	If the split vent is blocked, clean or replace it. If the flow regulator fails, replace it.
Carrier gas supply shortage	Check the supply pressure to the GC; it may be inadequate.

No peaks at all

Main Causes	Approach
Defective syringe	Clean and replace the syringes.
Improper column attachment position to the inlet and detector	Adjust the column insertion length to the position specified in the instruction manual of the GC system.
Column breakage	Check for broken columns.
Carrier gas leakage, insufficient supply	Check for gas leaks, mainly around the inlet. If the inlet septum is leaking, replace the septum. Check for proper supply flow rate at the detector outlet, column outlet, etc.
Detector abnormality	Check the condition of the detector. Check for filament breakage in the MS and TCD and frame ignition in the FID. Check the cables connecting the detector to the data processor.

All peaks reduced in size

Main Causes	Approach
Partial syringe blockage	Clean and replace the syringes.
Leakage from inlet	Check for leakage from the inlet. If the inlet septum is leaking, replace the septum.
Large split ratio	Optimize the split ratio.
Insufficient sampling time (in splitless injection)	Ensure that the injection is splitless at the time of injection. Optimize the sampling time.
Problem with the sample	Check the concentration, stability, and other properties of the sample and reconsider the sample preparation and storage methods.
Inlet temperature too low (especially when analyzing the high boiling–point components)	Check and optimize the inlet temperature.
Inadequate combination of the components to be measured and the detector	Check whether the detector is appropriate. Detectors with high selectivity might not be detected.
Misconfigured detector or integrator	Check whether the sensitivity setting of the detector is correct. Check that the attenuation setting of the integrator is correct.

Poor Reproducibility

Main Causes	Approach
Carrier gas leakage, insufficient supply	Check for gas leaks, mainly around the inlet. If the inlet septum is leaking, replace the septum. Check for proper supply flow rate at detector outlet, column outlet, etc.
Inappropriate injection conditions	Select a liner that is appropriate for the injection method and volume. If injecting manually, use an autosampler, as manual injection may be the cause of the discrimination.
Syringe failure, autosampler-setting condition failure	Some samples have not been collected. Clean and replace the syringes. For highly viscous samples, consider slowing down the syringe aspiration rate.
Liner contamination and deterioration	Clean or replace the liner. Depending on the specimen, consider selecting a liner with or without wool, or changing the wool material.
Contamination of column (liquid phase)	Conditioning of columns. Cut 50 cm off the inlet side of the column. If there is no improvement, replace the column.
Unstable split ratio	If the split ratio is excessively small, the split ratio is not stable. Adjust to the appropriate split ratio for the column and instrument.
Detector failure	Check the condition of the detector.

Ghost Peak Carryover

Main Causes	Approach
Residue in column (insufficient column conditioning, residual high boiling–point components)	If irregularities are detected and the peak width is broad, column residues are probably present. Often improved by column conditioning, but in some cases, around 50 cm must be cut from the inlet side of the column. If the cause is a high boiling–point component in the sample, change the oven-temperature-rise conditions to elute the sample.
Contamination of vials, caps (septums), and syringes	If the syringe is contaminated, clean or replace it. If the same vial is analyzed continuously, the septum is probably contaminated and should be replaced.
Inlet contamination	May be caused by liner contamination from inlet septum debris or sample residue. Clean or replace the liner. Replace the inlet septum.
Injection volume is too large	Depending on the injection volume, liner size, septum purge flow rate, and inlet temperature conditions, the sample may overflow from the liner, causing carryover. Select the appropriate injection conditions.

Decreased Column Performance

Main Causes	Approach
Insufficient purity of carrier gas (moisture and enzymes in carrier gas)	Columns (liquid phase) can rapidly degrade when temperature is increased in the presence of water and oxygen. Install a moisture removal filter and oxygen removal filter in the carrier gas line. If these filters are already installed, please replace the filters into new ones.
Insufficient purging during column conditioning	Before use (before raising the temperature), thoroughly purge the column with a carrier gas and condition the column under the recommended conditions. (See capillary column-handling instructions).
The introduced samples cause chemical damage to the column (liquid phase)	If the sample contains an inorganic base (KOH, NaOH, etc.), inorganic acid (HCI, HNO₃, HF, etc.), perfluoroacetic acid (CF₃COOH, C₂F₅COOH, etc.), salt, or another matrix that adversely affects the column (liquid phase), consider pretreatment or other methods.
Insufficient sample cleanup	If the sample contains a matrix that adversely affects the column (liquid phase), consider pretreatment, etc.
Inadequate analytical conditions	Pay special attention to the final temperature setting of the temperature increase in the column oven program. The heat resistance temperature of the column must not be exceeded.

3-8 Flooded Zones and Retention Gaps

4-2 Baseline Problems

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