[Readers Insight] Why Peak Fronting Occurs? Causes and Analysis

This article is written by Welch's contract writer Chromatography Mound. The content of the article presents a point of view from the author solely.

In the field of chromatographic analysis, developing a new method (such as expanding a testing scope) rarely proceeds without obstacles. Analysts frequently encounter issues including lack of retention, insufficient resolution, poor response, or distorted peak shapes.

To resolve these issues, identifying the underlying causes is the key. Without it, the problem remains difficult to resolve.

In this article, we explore specifically the causes of peak fronting. Peak fronting is a phenomenon where multiple causes lead to a same single result. Only by identifying the specific origin like a diagnostician can we apply the correct remedy.

Peak fronting is visually defined by a gradual, gentle leading edge and a steep, sharp trailing edge. The peak appears as if it is being "pulled" forward. In certain cases, a small "hump" or "shoulder" may also appear immediately preceding the main peak.

The most common cause of a gradual leading edge and steep trailing edge is sample overloading. This occurs when the amount of target analyte exceeds the capacity of the stationary phase, leading to the oversaturation of adsorption sites.

• Mechanism: The molecules that first enter the column occupy the available adsorption sites. Subsequent molecules, finding no available "positions," migrate through the column faster than the initial portion, thereby forming a fronting peak.
• Solutions: The most effective remedy is to reduce the injection mass, either by diluting the sample or decreasing the injection volume. This approach offers several technical advantages:
  • Ensures the concentration remains within the linear range.
  • Prevents contamination of the column and the overall system.
  • Reduces matrix effects when utilizing mass spectrometry (MS) detection.

A significant disparity in elution strength between the sample solvent and the mobile phase is another major cause of fronting.

• Mechanism: If the initial mobile phase has a high aqueous proportion while the sample is dissolved in a strong solvent (such as pure methanol or acetonitrile), the molecules at the front of the sample droplet will be eluted prematurely. These molecules migrate faster because they are not initially retained. Once the strong solvent is diluted by the mobile phase, normal retention is restored for the remaining molecules.
• Visual Indicator: This typically appears as a "hump" or "bulge" before the main peak. The severity of the fronting is directly related to the polarity difference between the sample solvent and the initial mobile phase.
• Solutions:
  • Decrease the injection volume.
  • Lower the proportion of strong solvent in the sample diluent.
  • Employ a solvent effect eliminator.