Derivatization / Reaction Headspace

Derivatization is a technique that can be used to increase sensitivity and chromatographic performance for certain compounds.

Compounds such as acids, alcohols, and amines are difficult to analyze due to the presence of reactive hydrogens. When attempting to analyze these types of compounds, they can react with the surface of the injection port or analytical column, resulting in tailing peaks and low response.

In addition, they may be highly soluble in the sample phase, resulting in very poor headspace partitioning and low response. Derivatization can improve their volatility and reduce the potential for surface adsorption once they enter the GC system.

Common reagents used to derivatize compounds of interest

Compound of Interest Derivatizing Reagent Resulting Derivative
Fatty acids Methanol with boron trifluoride Esterification
Glycerol Acetic anhydride with sodium carbonate Acetylation

Derivatization Techniques

Common derivatization techniques used in reaction headspace/GC include

  • Esterification
  • Acetylation
  • Silylation
  • Alkylation

Each of these derivatization techniques can be performed using the sample vial as the reaction vessel. Although derivatization can improve chromatographic performance and volatility for some compounds, derivatization reactions can introduce other problems into the analytical scheme:

  • Derivatization reagents, as well as by-products from derivatization reactions, can be volatile and may partition into the headspace along with the derivatization compounds. These extra volatile compounds can cause problems by eluting with similar retention times as the compounds of interest, causing either partial or complete coelutions.
  • Derivatization reactions are usually performed at elevated temperatures. Pressures within the sample vial may exceed the pressure handling capabilities of the vial or septa. Specially designed caps are available to vent excess pressure during derivatization reactions. It is important to use the correct vial and cap.