Method for Preparing Highly Viscous Organic Matter for IR Spectroscopy Analysis
Publication Date: 2014-Sep-29
The IP.com Prior Art Database
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METHOD FOR PREPARING HIGHLY VISCOUS ORGANIC MATTER FOR IR SPECTROSCOPY ANALYSIS
This subject disclosure describes a procedure to prepare pellets containing highly viscous organic matter such as bitumen for IR spectroscopy analysis. The method herein is described with respect to transmission Fourier-transform IR spectroscopy, but the method is broadly applicable to any IR spectroscopic technique. Quantitative transmission FT-IR analysis is traditionally performed using pellets made of an IR transparent matrix, such as potassium bromide (KBr), mixed with a solid sample. These solids are brittle and can therefore be mechanically reduced in particle size to a few microns using a mortar and pestle, mixer mill or other crushing apparatus. Liquids can be measured using a cell to hold the liquid but the analysis is typically qualitative for transmission FT-IR analysis. Neither of these techniques is effective for the quantitative analysis of highly viscous samples such as bitumen. This subject disclosure employs a cryogenic mill as an effective means of preparation of bitumen samples for IR spectroscopy as traditional KBr pellets. By mixing these samples at cryogenic temperatures, the bitumen becomes brittle enough to break down into micron-sized particles and be dispersed homogenously throughout the KBr matrix allowing for accurate quantitative analysis of the resulting IR spectra.
Matteson and Herron, 1993 described a technique for the quantitative analysis of minerals. The methodology was improved as shown in Herron et al, 1997 to quantify minerals to an accuracy of approximately ± 2 wt%. The ability to accurately quantify the components of the samples analyzed relies on three important steps in the sample preparation procedure:
1) The sample material must be reduced in particle size to a few microns. For solid earth samples, a mortar and pestle or other crushing apparatus is first used, followed by a micronizing mill. This step is necessary for the physics of the measurement to work - the particle size must be smaller than the wavelength of light used to excite the sample.
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2) The sample material is then mixed in a precisely known concentration with a carrier that is invisible in the infrared region of interest. In this case, potassium bromide (KBr) is used as the carrier. The amounts of sample material and KBr used have been selected to maximize the signal-to-noise ratio and to ensure that the measured spectrum falls within the linear region of Beer's law.
3) The sample material and KBr are mixed in a way that distributes the sample material homogenously throughout the KBr matrix. A heterogeneous sample will lead to non-linear absorption of the infrared light and the resulting spectrum becomes distorted rendering it inadequate for quantitative analysis.
Previous studies examining FT-IR infrared spectra of bitumen do not prepare KBr pellets containing bitumen but rather, use a cell to hold...