Electrospray film deposition for solvent-elimination infrared spectroscopy

The application of electrospray (ES) for quantitative transfer of analytes from solution to an internal reflection element for analysis by Attenuated Total Reflectance - Fourier Transform Infrared (ATR-FTIR) spectroscopy has been developed in this work. The method (ES-ATR-FTIR) is evaluated with nonvolatile and semivolatile organic and inorganic compounds dissolved in pure organic solvents, or organics in mixture with water. The technique demonstrates the capability for rapid solvent evaporation from dilute solutions, facilitating the creation of thin films that allow ATR-FTIR to generate transmission-mode-like spectra. ES-ATR-FTIR with multiple reflections displays a linear response (R2 = 0.95–0.99) in absorbance with the deposited mass and instrumental detection limit below 100 ng, which demonstrates potential for quantitative applications. The method is applicable when crystalline substances are present, even though the formation of particles restricts the upper limit of mass loadings relative to substances forming homogeneous films. In addition to the solvent, semivolatile compounds can evaporate during the ES process; the magnitude of losses will depend on solution composition and temperature.