title: Rapid, nondestructive estimation of surface polymer layer thickness using attenuated total reflection fourier transform infrared (ATR FT-IR) spectroscopy and synthetic spectra derived from optical principles.
abstract: We have developed a rapid, nondestructive analytical method that estimates the thickness of a surface polymer layer with high precision but unknown accuracy using a single attenuated total reflection Fourier transform infrared (ATR FT-IR) measurement. Because the method is rapid, nondestructive, and requires no sample preparation, it is ideal as a process analytical technique. Prior to implementation, the ATR FT-IR spectrum of the substrate layer pure component and the ATR FT-IR and real refractive index spectra of the surface layer pure component must be known. From these three input spectra a synthetic mid-infrared spectral matrix of surface layers 0 nm to 10,000 nm thick on substrate is created de novo. A minimum statistical distance match between a process sample's ATR FT-IR spectrum and the synthetic spectral matrix provides the thickness of that sample. We show that this method can be used to successfully estimate the thickness of polysulfobetaine surface modification, a hydrated polymeric surface layer covalently bonded onto a polyetherurethane substrate. A database of 1850 sample spectra was examined. Spectrochemical matrix-effect unknowns, such as the nonuniform and molecularly novel polysulfobetaine-polyetherurethane interface, were found to be minimal. A partial least squares regression analysis of the database spectra versus their thicknesses as calculated by the method described yielded an estimate of precision of ±52 nm.
authors.affiliation: Semprus BioSciences Inc., Cambridge, MA 02139, USA. andre.weinstock@semprusbio.com
authors.forename: B André
authors.initials: BA
authors.lastname: Weinstock
authors.forename: Linda M
authors.initials: LM
authors.lastname: Guiney
authors.forename: Christopher
authors.initials: C
authors.lastname: Loose
mesh_terms: D001622:Betaine / Q000031:analogs & derivatives / Q000737:chemistry; D016018:Least-Squares Analysis; D055620:Optical Phenomena; D011140:Polyurethanes / Q000737:chemistry*; D012031:Refractometry; D015203:Reproducibility of Results; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*
chemical_list: D011140:Polyurethanes; C115016:polyetherurethane; D001622:Betaine; C483727:sulfobetaine