Silica nanolayer coated capillary by hydrothermal sol–gel process for amines separation and detection of tyramine in food products

A hydrothermal sol–gel method for reproducible formation of silica nanolayer on the wall of silica capillaries was developed for electrochromatography. The formulation was optimized by observation of uniform gel formation on an optical microscope. The variables of the formulation include types of solvent, water-TEOS ratio, CTAB and urea contents, and mixing method. The procedure produced a coating of silica ca. 100 nm thick layer on the wall of the capillary. Surface morphology of the coating was characterized by SEM, contact angle and chemical composition by FT-IR spectroscopy and X-ray powder diffraction. The coating reduced the electroosmotic mobility producing enhanced separation performance. Eight standard amines (including tyramine and benzhydrylamine, as an internal standard) were separated with peak resolution R(s) ≥ 2 for all adjacent peaks and plate number N ≥ 3.0 × 10(4) m(-1). Calibration was linear from 5 to 200 µg L(-1), with r(2) > 0.9985 and instrumental LOD of 4.9 μg L(-1). Five samples of food products were diluted and analyzed for the amines using the coated capillary and only tyramine was detected. Intra-day and inter-day precisions were less than 1.2%RSD. Percent recoveries of spiked tyramine in samples were 95 ± 3 to 106 ± 7% (n = 3).