Forensic Science Applications of Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS): I. Principles, Sampling Methods, and Advantages

Abstract

Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) is a recently developed technique that offers several significant advantages over conventional methods of sampling solids. Some of these include: (1) minimal sample preparation (no sample preparation in a few cases); (2) a very wide range of sample concentrations which yield useful spectra; and (3) a very high sensitivity (less than 100 ng in some cases). DRIFTS has been applied to the analysis of a number of materials of forensic science interest. Specific applications for a variety of evidence types have been found; this work is therefore presented as a series. This paper presents the principles of the technique and examples of the sampling methods, including a microsampling method for liquids. Some of the unique advantages that DRIFTS offers for forensic science work, including better characterization of many compounds, are illustrated. In addition, an explanation of these DRIFTS features is discussed.

Infrared Spectra of U.S. Automobile Original Finishes. VII. Extended Range FT‐IR and XRF Analyses of Inorganic Pigments In Situ—Nickel Titanate and Chrome Titanate

“…Some pigment powders were additionally analyzed either neat or diluted with excess CsI and pressed between both anvils of the DAC; diluted with CsI and analyzed with a Digilab diffuse reflectance (DRIFTS) accessory (13); or diluted with excess CsI and pressed into a pellet. Unless otherwise indicated, the pigment spectra that are depicted were obtained using the single anvil method.…”

“…Spectral baselines were not flattened, however. Reflectance spectra of pigments obtained using the DRIFTS accessory were converted to a transmittance format (13).…”

“…None of these other inorganic pigments produced an effect as pronounced as that of rutile and the titanates, but there appear to be at least two reasons for this: (1) there is a wavelength term in the Fresnel equation (13) for specular reflection that indicates that reflection increases somewhat with wavelength; this effect is thus likely to be more evident for a far‐infrared band than one that occurs at higher frequencies; and (2) the very wide breadth of the rutile/titanate absorption permits this effect to be more noticeable (the index of refraction is normally changing most rapidly near the peak of an absorption band, but for most compounds, a relatively sharp peak is involved).…”

“…The DAC is thus clearly the source of this effect. Three different low-pressure diamond anvil cells and a high-pressure diamond anvil cell (13) were used on five different FT-IR instruments/beam condensers over the course of two decades. All of these configurations produced similar results, so specific analysis geometry is not a factor.…”

Some Advances in Fourier Transform Infrared Transflection Analysis and Potential Applications in Forensic Chemistry

“…The use of the transflection technique in the mid-infrared, although used sporadically in the past, [12][13][14][15][16][17] has been generally ignored as a standard methodology. 4,[18][19][20][21] Yet transflection in this region has, as demonstrated in this paper, the potential for high sensitivity and signal-to-noise ratio.…”