Attenuated total reflectance (ATR) is the current preferred method for quantitative and neat sample analysis in the mid-infrared region. ATR, while robust and user-friendly, has disadvantages. Wavelength dependent penetration depths produce vibrational band intensities dissimilar to those from traditional transmission measurements and samples may be destroyed when cleaning the ATR crystal. Here, a quantitative and non-destructive method capable of neat samples analysis in the mid-infrared range is presented, based on diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). A sample holder, dubbed a “Button”, is fabricated by spot welding wire mesh onto a stainless-steel reflective backing. Buttons are an adjustable platform that can be customized through modification of mesh size, wire diameter, and depth of the sample containment area, among other parameters. A sliding sample stage, used with sample and reference button holders, allows for quick analyses and minimizes artifacts caused by instrument purge variations.<br/>DRIFTS analyses employing Button sample holders for solid and liquid samples will be demonstrated. Spectrum features reveal qualitative aspects of neat sample compositions. Calibration curves are linear for solids, liquids, and solids deposited from aqueous solutions for concentrations ranging from 1.25-20%. Results obtained for a 200 ng Benzoic acid solution confirm that nanogram detection limits can be achieved. Changes to baseline slope and band intensities vary with the amount of solid sample loaded onto a Button. By rubbing the abrasive metal mesh against surfaces, solid material can be transferred to the button and subsequently analyzed. Unlike ATR, samples loaded onto Buttons can be stored and re-analyzed at a later time. In summary, DRIFTS Buttons provide a quick, cheap, reusable, user-friendly method for mid-infrared analysis of neat solids and liquids. Unlike ATR, vibrational spectra obtained by the DRIFTS Button technique are similar to those obtained by transmission measurements.

Buttons: Simple, inexpensive, and reusable sample holders for neat sample mid-infrared assays

ACS Fall 2020 Virtual Meeting

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