Ionic liquids as silica deactivating agents in gas chromatography for direct analysis of primary amines in water

Analysis of primary amines in aqueous samples remains a challenging analytical issue. The preferred approach by gas chromatography is hampered by interactions of free silanol groups with the highly reactive amine groups, resulting in inconsistent measurements. Here, we report a method for direct analysis of aliphatic amines and diamines in aqueous samples by gas chromatography (GC) with silanol deactivation using ionic liquids (ILs). ILs including trihexyl(tetradecyl)phosphonium bis 2,4,4-(trimethylpentyl)phosphinate (Cyphos IL-104), 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide [pmim][Tf2N] and N″-ethyl-N,N,N′,N′-tetramethylguanidinium tris(pentafluoroethyl)trifluorophosphate [etmg][FAP] were tested as deactivating media for the GC liner. Solutions of these ILs in methanol were injected in the system prior to the analysis of primary amines. Butane-1,4-diamine (putrescine, BDA) was used as a reference amine. The best results were obtained using the imidazolium IL [pmim][Tf2N]. With this deactivator, excellent reproducibility of the analysis was achieved, and the detection limit of BDA was as low as 1 mM. The applicability of the method was proven for the analysis of two different primary amines (C4–C5) and pentane-1,5-diamine.

► Gas chromatography of primary amines in water remains challenging. ► Deactivation of silanol groups in the pre-column is needed. ► Ionic liquids as potential deactivation media. ► Significant improvement of the analysis with [pmim][Tf2N]. ► Very robust method with 400 injections per deactivation.