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PROBLEMS WITH PEAK SHAPE

Poor peak shape can cause a loss of resolution between adjoining peaks, it can lead to poor injection to injection reproducibility, or it may cause an injection to fail method acceptance criteria. Poor peak shape includes issues such as tailing, fronting, split peaks, and shouldered peaks.

 

The causes of poor peak shape are varied. They include everything from poorly developed methods, to contaminated columns or in other parts of the system, to extra system volume or poor system connections.

 

The following chart covers some of these common problems and possible remedies.

Problem

Indication

Cause

Solution

One or a few peaks tailing

Unexpected analyze interaction with solid support or stationary phase

All peaks tailing

Poor Connections in system

Void in Column

Use base deactivated, or hybrid silica materials. Old style silica have active sites on the surface that can have unintended interaction with sample analyze

 

Add a mobile phase modifier to the system such as TEA

Ensure that all tubing ends are cleanly and squarely cut.

 

Make sure that all nuts and ferrules are of the correct shape and tubing depth is correct for all fittings. Different manufactures have different tolerances, and they are not all interchangeable.

 

Use PEEK or universal spring loaded connecting tubing.

Replace Column

Initial Peaks fronting

Dirty guard Column

Replace Guard

Dirty column frit

Replace frit

All peaks fronting

Too strong a sample solvent

Samples should be dissolved in mobile phase or solvent weaker than mobile phase.

Column overload

Reduce injection volume

Reduce sample concentrations.

Split Peaks

Shoulder on 1 or 2 peaks

Shoulder on all peaks

Void or channel in column

Use a column with larger i.d.

Back flush or replace column

Dirty column frit

Replace frit

Dirty Column

Sample solvent not suitable for use with mobile phase

Back flush or replace column

Ensure that sample and mobile phase solvents are compatible make any necessary adjustments

Mobile phase is at 1 pH near the pKa of the analyze

Dirty Inlet frit

Dirty Guard Column

Dirty Column

Adjust pH of mobile phase to be at least 2 pH units away from the pKa of the sample analyzes

 

Adjust mobile phase to separate the 2 peaks

Replace frit

Replace Guard

Back flush or replace

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