Low-Cost Infrared Microspectroscopy
times [5]. A large factor in reduced collec- tion time comes from the fact that FTIR spectrometers benefit from the multiplex advantage, or the ability to measure all wavelengths simultaneously, compared to the serial data collection of dispersive instruments. Te combination of this multi- plex advantage and signal averaging enables spectra with a very high signal-to-noise ratio (SNR) to be generated [5]. Interest in using FTIR microspectroscopy to study small particles was revisited in the late 1970s fol- lowing developments in the field of FTIR spectroscopy along with the need to identify microscopic contaminants in the electronics and semiconductor industries [6]. Several studies have highlighted the use
Figure 2: Reference spectrum of indigo dye (top) and the result of a subtraction of an undyed wool fiber spectrum from that of a blue Paracas Indian archeological fiber (bottom). Absorptions identifying the presence of indigo are marked with an “X.” (Reprinted with permission from Analytical Chemistry [3]).
of FTIR instruments and beam condensers in the study of microscopic samples. In 1977 Cournoyer et al. [7] demonstrated the use of FTIR in the detection of samples whose mass was less than 1 ng. In this work, the authors studied various samples using the first com- mercially available FTIR instrument, the Digilab FTS-14 FTIR spectrometer, which
possessed a standard nichrome wire source, a deuterated trigly- cine sulfate (DTGS) detector, and a Perkin-Elmer 8× beam con- denser. In their work, they successfully analyzed a 6 ng sample of triphenyl phosphate from a manufacturing environment, 3.4 ng of a cellulose acetate film with a 100 μm aperture, and 0.9 ng of the same sample with a 50 μm aperture. Te signal in the spectrum of the 0.9 ng sample was sufficient for the material to be identified. Te authors also demonstrated that with extended scanning (≈ 40 hours) absorptions associated with 90 picograms of triphenyl phosphate in the film were recognizable [7]. In simi- lar work, Lacy et al. used FTIR to identify talc particles in an ali- phatic oil matrix on a ceramic reader head from a computer disk memory-readout assembly. Tey also used FTIR spectroscopy to determine the identity of a Nylon particle that was lodged between a relay contact from a reaction-control system and identified marking ink on a microprocessor chip [8]. Another study highlighted the integration of the original PE Model 85 infrared microscope with the FTIR instruments of the day. A Digilab Model FTS-20C spectrophotometer was modified to accept a 30-year-old Perkin Elmer Model 85 microscope. In this work, the combined system was capable of recording spectra of particles as small as 10–20 μm in diameter. Further, a variety of sample preparation techniques were highlighted [9]. In 1983 Digilab introduced the first commercially avail-
Figure 3: The Perkin Elmer 85 infrared microscope. 28
able FTIR microscope, the Digilab UMA 100, which was designed to be integrated with the Digilab FTS-14 FTIR. Tis effort was followed by a number of infrared accessory manu- facturers such as Spectra-Tech Inc. and other manufacturers of FTIR instruments who continue to build and market increas- ingly complex and sophisticated microscope systems. Tese systems not only perform infrared measurements, but can also be used in a wide variety of techniques associated with optical microscopy [10]. While imaging and mapping are very useful in research environments, the basic applications of infrared
www.microscopy-today.com • 2020 March
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76
