by Narinder K. Mehta, Javier Goenaga-Polo, Samuel P. Hernandez-Rivera, David Hernandez, Peter J. Melling, and Mary A. Thomson, Remspec Corporation A fiber-optic, mid-IR spectroscopy probe combined with a grazing-angle reflectance sampling head can be used as a solvent-free in situ method for validating cleanliness with substantial improvement in accuracy.