1Harrick Scientific Products, Inc.

	Diamond ATR has become one of the most commonly used FT-IR spectroscopy methods. However, the strong diamond lattice bands in the 2300–1900 cm

 region make it difficult to measure the functional groups from nitriles, isocyanates, isothiocyanates, diimides, azides, and ketenes that would normally appear in that region. This applications note compares the sensitivity of a single-reflection ATR to multiple-reflection ATR for the nitrile functional group infrared transition.

	Infrared spectra were collected on an FT-IR spectrometer equipped with the Harrick DiaMaxATR™ single-reflection high-throughput diamond ATR accessory or ConcentratIR2 multiple-reflection diamond ATR (see Figure 1). The system was purged to remove water vapor and CO

resolution, and signal averaged over 32 scans. The spectra were referenced to the clean ATR crystal.


	Figure 1: Two diamond ATRs: Single reflection DiaMaxATR (left) and ConcentratIR2 (right).

	The sample used here was a High Five Nitrile Disposable Glove (lightly powdered, textured, P/N N842). For the single-reflection ATR measurement, a portion of the glove was pressed against the ATR crystal using the maximum force supplied by the build-in pressure applicator. For the multiple-reflection ATR measurements, the sample was gently pressed against the ATR crystal with compressible foam to fill the trough, and to apply force as uniformly as possible.

	Figure 2 shows the two spectra. The upper spectrum measured with the multiple-reflection ATR shows only noise in the 2300–1900 cm

 region, due to the high absorbance of diamond in that region. The lower spectrum, however, clearly shows the C≡N stretch at 2238 cm

. Another weaker band is also apparent in the single-reflection ATR spectrum at 2162 cm

, possibly indicating the presence of an alkyne group.


	Figure 2: Diamond ATR spectra of a nitrile glove measured using a multiple reflection ATR (blue) and a single reflection ATR (red).

	The Harrick DiaMaxATR high throughput, single reflection diamond ATR is effective at measuring functional groups that are frequently obscured by the strong diamond lattice bands in the 2300–1900 cm

 region. This makes it more suitable for analysis of the function groups in that region, including nitriles, isocyanates, isothiocyanates, diimides, azides, and ketenes.


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Articles

This applications note compares
the sensitivity of a single-reflection ATR to multiple-reflection ATR for the nitrile functional group infrared transition.

A Diamond ATR-FTIR Study of Nitriles

	Cannabinoids and opiates have been used for medicinal purposes for thousands of years for relief of pain and seizures. In the early 1900s, an opioid epidemic resulted in restrictions on opiates. Years later, tighter restrictions were also placed on marijuana-one source of cannabinoids-although medical marijuana and cannabinoids have become increasingly legal and available in some states in recent years. The past few years have again seen an increase in opioid overdoses and even tighter regulation to prevent abuse, addiction, and possible deaths. Despite advances in medicine in the interim, there are few therapeutic alternatives to the opioids with the notable exception of cannabinoids.

	At least 100 cannabinoids have been found to have medicinal properties. The most commonly known are CBD (cannabidiol) and THC (tetrahydrocannabinol). These are extracted from hemp and marijuana plants, which are botanically distinct cannabis species. CBD extracted from hemp is available without prescription as a supplement, and contains no THC. Cannibinoids extracted from marijuana include CBD as well as some THC component, and hence are highly regulated because of the psychoactive properties of THC. CBD does not appear to have any intoxicating effects such as those caused by THC. Here, several formulations of cannabinoids are examined using mid-infrared diamond ATR spectroscopy.

	Infrared spectra were collected on an FT-IR spectrometer equipped with the Harrick DiaMaxATR™ single-reflection high-throughput diamond ATR accessory. The system was purged to remove CO

and water vapor. Spectra were collected at 8 cm

resolution and signal averaged over 32 scans. The spectra were referenced to the clean ATR crystal.

	Four formulations were investigated. The capsules and tablets were cut open to examine the enclosed components. Two of the samples were from hemp: Plus+CBD Oil™ softgels (liquid; 5 mg CBDA/CBD in extra virgin olive oil) and Plus+CBD Oil™ capsules (powder; 10 mg CBA in modified food starch, cellulose, silicon dioxide, and magnesium stearate). The other two were medicinal marijuana from different suppliers, designated here as A (liquid from a gel tablet; 8.5 mg THC, 8.5 mg CBD in coconut oil) and B (paste from a capsule; 0.7 mg THC, 4.3 mg CBD in coconut oil). Small aliquots of the samples were placed on the ATR crystal. Pressure was applied to compress the powdered sample against the diamond.

	Figure 1 shows the resulting spectra. The two formulations from hemp have a band at 3010 cm

 which is not present in the marijuana samples. All the samples except the Plus+CBD Oil™ capsules show a weak band at 3477 cm

 due to a phenol OH stretch. The Plus+CBD Oil™ capsules are the only formulation that contains cellulose and the broader OH stretch from cellulose may be masking the phenol OH band. The Plus+CBD Oil™ capsules also have a strong band at 1047 cm

 from cellulose. All four samples show the characteristic bands of cannabinoids around 1624, 1581, 1510, 1462, and 1374 cm


	Figure 1: Diamond ATR spectra of four medicinally beneficial cannaboid formulations: Plus+CBD Oil™ Softgels (black), Plus+CBD Oil™ Capsules (green), A (red), and B (blue).

	The Harrick DiaMaxATR, high throughput, single reflection ATR is effective at revealing spectral differences among the medicinally beneficial cannabinoid formulations available on the market.


	141 Tompkins Ave., Box 277, Pleasantville, NY 10570
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A Diamond ATR-FTIR Study of Various Medicinal Cannabinoid Formulations

	Heating foods and beverages can lead to a variety of chemical changes. These changes can effect storage lifetime and nutritional value. Hence there is a continuing need for highly sensitive methods to detect these changes.

	This application note explores the potential of using a high-throughput single-reflection diamond ATR to detect structural changes in egg yolk upon heating.

	Infrared spectra were collected on an FT-IR spectrometer equipped with the Harrick DiaMaxATR™ single-reflection diamond ATR accessory with its Temperature Controlled Liquid Cell (Figure 1). The system was purged to remove water vapor and CO

 resolution and signal averaged over 32 scans. A background was collected from the clean ATR crystal at ambient temperature.


	Figure 1: The DiaMaxATR™ with Temperature Controlled Liquid Cell.

	The egg yolk was separated from the egg white, and ~0.3 mL of the yolk was injected into the heatable cell. A sample spectrum was collected at ambient temperature. Then the cell was heated to 100 °C using the compatible Temperature Controller. Another spectrum was collected when the cell temperature stabilized and at 2 min intervals thereafter. Data collection was controlled by Harrick ATC-Link™ software.

	The resulting spectra are shown in Figure 2. With increasing temperature, the OH stretching band around 3500 cm

 decreases in intensity as the water evaporates from the yolk and begins to appear as two underlying broad bands, centered around 3390 cm

. The former indicates the presence of amines and the latter carboxylic acids, both of which become more concentrated in the yolk as the water is driven off. In addition, changes are evident in the 1500 to 1700 cm

 region, as expected from changes in the proteins induced by heating. The amide I bands at 1650 cm

 are likely from the α and β helixes, respectively. The broad underlying band in that region may indicate unordered amides. The peaks at 1560 cm

	Single reflection ATR spectroscopy is valuable for examining thermally induced changes in materials. Changes in the water concentration and amide bands of egg yolk were observed using the Harrick DiaMaxATR accessory. Further analysis is possible to obtain more rigorous identification of the heat-induced structural changes.


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Single reflection ATR spectroscopy is valuable for examining thermally induced changes in materials. Changes in the water concentration and amide bands of egg yolk were observed using the Harrick DiaMaxATR accessory. Further analysis is possible to obtain more rigorous identification of the heat-induced structural changes.

An FT-IR Spectroscopic Study of Cooking an Egg Yolk on a Single-Reflection Diamond ATR

Grazing angle Ge ATR spectroscopy is extremely sensitive to monolayers and thin films on high refractive index substrates such as Si. As with any ATR method, the sensitivity increases as the critical angle is approached, as demonstrated herein.

	Monolayers and other thin coatings on Si and other high refractive index substrates are of key importance in materials science, bioscience, synthetic organic, and semiconductor research. These films are often close to the FTIR detection limit so methods that improve sensitivity are vital. Traditionally, these samples were examined by transmission or grazing angle specular reflectance spectroscopy. Grazing angle Ge-ATR has recently gained wider use because of its higher sensitivity. Grazing angle Ge-ATR measurements have typically been recorded at 65°, an angle sufficiently above the critical angle for the Si-Ge interface, 58.7°.

	This note explores the increased sensitivity gained by optimizing the incident angle and also discusses the potential spectral anomalies if the nominal critical angle of a given sample is exceeded.

	The grazing angle Ge-ATR measurements were carried out in a commercial FTIR spectrometer, using Harrick's VariGATR(tm) accessory at selected incident angles from 60° to 65° (see Figure 1). Spectra were collected at an 8 cm

 resolution and signal averaged over 32 scans. The samples investigated were thin films on Si substrates. Each sample was pressed against the ATR crystal using the same force using the VariGATR's built-in pressure applicator and force sensor.


	Figure 1: The VariGATR™ shown with its Force Sensor.

	Figures 2a and 2b show spectra recorded from two different samples at several incident angles. Both spectra have higher band intensities at the lowest angle measured. However, the spectrum of sample B shows significant dispersion effects at 60° which may complicate interpretation. These include a sloping baseline and a visible step between the high and low wavenumber edges of the bands. These effects are not apparent in the spectrum of sample A.


	Figure 2: (a): ATR spectrum of sample A recorded at an incident angle of 65° (red), 63° (blue), and 60° (black) with an applied force of 722 N. (b): ATR spectrum of sample B recorded at an incident angle of 65° (blue) and 60° (black) with an applied force of 700 N.

	In conclusion, it is clear that selecting the incident angle to approach the critical angle does increase sensitivity. However, for ease of interpretation, the incident angle should be optimized for greatest sensitivity without significant dispersion effects.


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Monolayers and other thin coatings on Si and other high refractive index substrates are of key importance in materials science, bioscience, synthetic organic, and semiconductor research.

Optimized Grazing Angle Ge-ATR of Monolayers and Thin Films on Si

	Molded rubber products, like o-rings and gaskets, are typically coated with a release agent during manufacturing to facilitate the removal from the mold. Detecting the release agent is important for manufacturing since improper application can cause the o-rings to adhere unexpectedly to the mold.

	Measuring the release agent on molded rubber products by infrared spectroscopy presents several challenges because the release agent layer is typically very thin and many base materials are carbon filled, and molded into small or unusual shapes. Thus, analysis requires a surface sampling technique with a relatively small sampling area, such as single-reflection ATR.

	This applications note demonstrates the use of ATR to distinguish o-ring release agents from the underlying fluoroelastomer.

	A fluoroelastomer o-ring was investigated using the Harrick MVP-Pro in conjunction with a commercial FT-IR spectrometer. The MVP-Pro, shown in Figure 1, is a single reflection ATR accessory with a 45° incident angle and a 0.5 mm diameter sampling area on its Si crystal. All infrared spectra were collected with an 8 cm

 resolution, averaged over 32 scans. Two spectra were recorded: one of the exterior of a black fluoropolyer (FKM) o-ring and another from the interior slice of the o-ring.

	Figure 2 shows the ATR spectra of the FKM o-ring, including the outer surface, the inner substrate, and the resulting difference. The measured spectra show characteristics typical of a poly(aliphatic) fluoride, as expected. The strong similarity between the spectra indicates that the release agent coating the o-ring is extremely thin. Slight spectral differences can be seen around 1020 cm

. Subtracting the two spectra results in the spectrum shown in black, which is clearly identifiable as silicone oil. Silicones are one of the materials frequently used as a release agent.


	Figure 2: ATR spectra of the o-ring: exterior (blue), interior (red) and subtraction result (black).

	From the infrared spectra presented here, it is clear that the release agent can be distinguished from the bulk molded rubber using Si micro-ATR methods and the MVP-Pro.