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Figure 1. MultiLoop-MIR™ installed on the FiberMate2.
New fiber manufacturing techniques combined with the high performance of modern FTIR spectrometers now make it possible to offer a fiber optic system for use with the DTGS detectors that are standard with most FTIR spectrometers. This system allows data collection over the entire mid-IR.
This system, the MultiLoop-MIR™, features two fiber optic probes with readily replaceable sampling tips. One probe operates over the fingerprint region, from 2000 to 600 cm-1, while the second covers the remaining mid-IR, from 6500 to 1700 cm-1. The probes connect to a fiber optic coupler, such as Harrick's FiberMate2, using standard SMA connectors. Probe tips are affixed onto the end of the probes to provide a leak-free probe assembly that can be dipped into or pressed gently into liquid, pastes, and soft solids. These tips are the only part of the MultiLoop-MIR™ that comes in contact with the sample, and they are easily replaced as needed.
The MultiLoop-MIR™ effectively provides two reflections from the sample as compared to single reflection ATR at 45° with a ZnSe crystal. It has excellent throughput for an infrared fiber optic system, allowing data collection with a DTGS detector.
Several examples are shown below using the MultiLoop-MIR™ with the FiberMate2 (see Figure 2). For these measurements, the spectrometer set for 64 scans at 8cm-1 resolution. The entire mid-infrared spectrum was measured using the two fiber probes and tips. The chalcogenide probe was used for 4000cm-1 to 1520cm-1 and the silver halide probe for the 1530cm-1 to 600cm-1 region. The spectra were baseline corrected and joined together to show the full spectral range.
Figures 2 and 3 show spectra of three different liquids. The two children's analgesics shown in Figure 2 are clearly distinguishable from each other in the fingerprint region. The spectrum of a wine sample (Figure 3) shows characteristics from the organic component of the grapes, in addition to the strong aqueous bands.
Figures 4 and 5 demonstrate using the MultiLoop-MIR™ for solid sampling. The silicone rubber tape is soft and flexible, so good contact was readily obtained between the sampling tip and the tape, as shown by the strong band intensities. The peak intensities in Figure 5 are much weaker, indicating that the contact with this sample was not as good. Yet the spectrum is clearly identifiable as polyester. Note: pressing the sampling tip against solid samples reduces the lifetime of the tip and is only recommended for use with soft solids.
The MultiLoop-MIR™ provides a quick and easy method for quantitative and qualitative in-situ analysis of liquids, pastes, and soft solids within one meter of the spectrometer.
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Figure 2. ATR Spectra of Children's Liquid Pain-Relievers Motrin (black) and Tylenol (blue).
Figure 3. ATR Spectrum of Kouros White Wine.
Figure 4. ATR Spectrum of Silicone Rubber Tape.
Figure 5. ATR Spectrum of a Plastic Toy Fish. and Water (lower).
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