MAGIC-LC/FT-IR Spectrometry with Buffered Solvent Systems

Abstract

The first demonstration of identifiable infrared (IR) spectra obtained from buffered (volatile and nonvolatile buffers) mobile phases using the Monodisperse Aerosol Generator Interface for Combining Liquid Chromatography with Fourier Transform Infrared (MAGIC-LC/FT-IR) spectrometry is described. Ammonium acetate, a volatile buffer, was used to buffer an 80:20 acetonitrile: water mobile phase to pH 5.0. Caffeine was deposited from this buffered mobile phase, and the spectrum was used as a reference to compare with caffeine spectra obtained from nonvolatile buffered mobile phases. The two nonvolatile buffers used were potassium hydrogen phthalate (KHP) and potassium dihydrogen phosphate (KH₂PO₄). The KH₂PO₄ was used to buffer an acetonitrile:water mobile phase and a methanol:water mobile phase, whereas the KHP buffer was used only in a methanoh:water mobile phase. Samples of caffeine were deposited from each of the above buffer systems along with the nonvolatile buffer. Infrared spectra of caffeine were obtained by spectral subtraction of previously stored buffer spectra from the caffeine:buffer spectra. The resulting spectra were identical to a caffeine reference spectrum.