Rapid fluorimetric assay for primary amine groups in water samples

Abstract.

Bond Elut C₁₈ solid-phase extraction cartridges were used for pre-concentration followed by derivatization with o-phthaldialdehyde-N-acetylcysteine (OPA-NAC) of primary amines in water. Optimal conditions were: conditioning the cartridges with borate buffer pH 10.4, retention of the primary amines, addition of the OPA-NAC(3.7 mmol L^–1) 1:1 molar ratio and borate buffer pH 8, elution of the isoindol with MeOH-borate buffer (9:1) pH 10.2 and fluorescence measurement. The equations of the calibration graphs for methylamine, ethylamine, propylamine, butylamine, pentylamine, and β-phenylethylamine at λ_excitation=330 nm and λ_emission=440 nm, in the optimal conditions are presented. The solid-phase extraction procedure improved ten times the detection limits of the solution derivatization. Those values are in the 0.01–0.06 mg L^–1 interval in function of the amine. Also, it is possible to estimate the total primary aliphatic amine concentration in water, expressed as molar concentration of –NH₂ group or –NH₂-N mg L^–1. On the basis of these studies, the method was applied for the determination of primary amino groups in tap, ground, factory and source water samples.