Meridian™ SplitPea™ Diamond ATR

Additional Information

This micro-horizontal diamond ATR accessory is ideal for analyzing a variety of samples, including hard solids, corrosive liquids and abrasive materials. Samples, which are difficult to analyze by conventional infrared spectroscopes, such as fibers, rocks, paints, and microliters of liquids or pastes, are easily examined with the Meridian™.

The Meridian™ can be configured for ATR or specular reflectance, simply by changing the sample holder. In its ATR mode, the Meridian™ features a removable holder for easy sample insertion and crystal cleaning. For specular reflection and pre-alignment, the Meridian™ features a removable sample holder and reference mirror. The Meridian™ is enclosed in a purgable box for rapid sample exchange without interrupting the purge of the FT-IR system.

An illustration of the Meridian™ is shown in Figure 1. Two mirrors, M1 and M2, direct the infrared beam to an ellipsoidal mirror, M3, which focuses the light onto the sample. The radiation reflected from the sample is collected by a second ellipsoid, M4. Mirrors M5 and M6 direct radiation reflected from M4 to the detector of the spectrometer. This configuration provides a six times linear reduction of the source image on the sampling surface.

For ATR, the Meridian™ comes with one diamond ATR crystal. Diamond is extremely inert, allowing the analysis of highly corrosive materials. It also has a low friction coefficient, so samples do not adhere strongly to the surface, making sample clean-up simple and straightforward. Furthermore, diamond is an extremely hard material. This permits the application of high clamping pressures to ensure good contact between the ATR crystal and the sample, even for samples as hard as rocks. Generally, lower pressures are required to achieve the good contact needed in ATR than are needed to flatten the sample for transmission studies. Thus fewer chemical and physical changes will be induced in the sample with the Meridian™ than with a high pressure diamond anvil cell.




Figure 2. Focusing Effects of a Hemisphere.

The Meridian™ diamond ATR crystal is a 3-mm diameter hemisphere. This further focuses the incident radiation onto the sample (see Figure 2), providing an additional reduction of the source image. For such a short pathlength, diamond is virtually transparent in the useful range of the far and mid-infrared. The diamond ATR crystal is faceted on the edge of its flat surface to provide a sampling area that is 500 µm in diameter, slightly larger than the hot spot on the crystal. This makes it easier to position small samples and maximize the clamping pressure. Because of the small size of this island, the pressure plate applies localized pressure to the sample improving contact between the sample and the ATR crystal, allowing high contact pressures to be achieved.

For applications versatility, ZnSe, Ge, and Si crystals are also available. This selection offers a variety of sampling depths and volumes.

The Meridian™ is available with a ViewThruPress™. This configuration is recommended for analyzing samples such as fibers, spots on transparent substrates, and powders. The ViewThruPress™ provides a 50X magnification of the sampling area and features precision adjustments for aligning the viewer over the active sampling area of the crystal. Its unique design permits the sample to be viewed as it is compressed against the crystal. The ViewThruPress™ also features an independent adjustment for focusing on the image. For liquid sampling, a Flow-Through Liquid Cell is available for use with the Meridian™. This cell is o-ring sealed and features two luer fittings. For analysis of powder with minimal spillage, a Powder Retainer is included with this ATR accessory. Both the flow-through liquid cell and powder retainer conveniently clamp onto the ATR holder.

In addition, heatable sampling plates are available for sampling at temperatures up to 200°C with the diamond or Si ATR crystals and to 100°C with a Ge ATR crystal. These sampling plates feature a gasket-sealed ATR crystal, K-type thermocouple, and 24V heater. These are designed for use with the Harrick Temperature Controller.




Figure 3. The ATR Spectra of Several Different Types of Rocks.

Representative infrared ATR spectra recorded with the Meridian™ are shown in Figures 3 through 6. Figure 3 shows the spectra of three different types of natural rock. These rocks are composed primarily of Lazurite (3Na₂O₃^.3Al₂O₃^.6SiO₂^.Na₂S), Malachite (CuCO₃^.Cu(OH)₂), and Marble (CaCO₃ or CaCO₃^.MgCO₃). The Meridan™ readily exposes the characteristic features of these materials.




Figure 4. The ATR Spectra of the Interior and Exterior of a Weathered Clam Shell.

Figure 4 shows infrared spectra from a clam shell collected from a beach on Cape Cod. The ATR spectrum of the exterior surface has a greater contribution from the C-H and O-H bands, as would be expected from its greater exposure to the underwater plant life.



Figure 5. The ATR Spectrum of Easy Off™5 Oven Cleaner.

In addition to physically hard samples, the Meridian can be used to examine corrosive materials. Figure 5 shows the infrared spectrum of Easy Off™5 Oven Cleaner, whose active ingredient is sodium hydroxide. This highly corrosive material attacks most ATR crystal materials but does not affect diamond. For this measurement, a small drop of oven cleaner was placed on the sampling surface of the diamond ATR crystal. Note that this type of sample could also be examined using the the Flow-Through Liquid Cell (UNS-LCF) for the Meridian™.



Figure 6. The ATR Spectra of Two Types of Wax.

Figures 3 through 5 illustrate the use of the Meridian™ with materials that are typically difficult to examine. The Meridian™ easily analyzes more routine samples, as demonstrated in Figure 6. Here, small spectral differences in the chemical composition of two waxes are evident. As demonstrated by the above examples, the Meridian™ diamond ATR micro-sampler is a powerful tool for examining a wide range of samples, including corrosive liquids, abrasive powders, and extremely hard solids in addition to those samples routinely analyzed by ATR spectroscopy.