FTIR microscope systems allow the analysis of extremely small samples (<250 μm) using infrared spectroscopy. Mapping experiments utilizing a single-element detector can provide infrared image data of a larger area of a sample with a defined spatial resolution, but at an extremely low rate of data acquisition due to the single-point nature of the standard microscope detector. The application of multielement detectors to imaging experiments greatly increases the speed of data acquisition, enabling the imaging of larger samples in a reduced period of time. Focal plane array (FPA) detectors can be used for infrared imaging with step-scan instruments, but the development of linear-array (LA) detectors for imaging permits the use of a standard infrared instrument and has decreased the overall cost of the imaging system. Thus, the imaging technique has been extended to a greater variety of users and samples, given the lower cost of the instrument systems that incorporate this type of detector.
There are numerous applications for FTIR microscopy and imaging systems, including polymer analysis, pharmaceutical and materials analysis, forensics investigations, semiconductors, and biochemistry and chemical analysis. For almost any sample that can be scanned with a traditional infrared method to obtain macro data from the sample, the FTIR microscope can be used to collect infrared spectra from a much smaller, defined area of the sample. FTIR microscopy and imaging systems can provide a simple spectrum of a very small contaminant in a larger matrix, or detailed information about the distribution of the chemical constituents or other types of spatial information, i.e., the variation and distribution of layers in a polymer laminate.
Traditional FTIR microscope and/or imaging systems have generally been a “one-size-fits-all” type of accessory, either specified at the time of instrument purchase or added later at a significant cost to the user. Some options may be upgradeable, such as additional cassegrains or software features, but generally, any feature required for future use has to be purchased as part of the initial FTIR microscope or imaging system. FTIR microscopy and imaging systems are also often limited to research grade FTIR instruments and are not generally integrated with an entry-level instrument. In the case of imaging systems, the FPA detector has generally been restricted for use with a step-scan instrument, further increasing the initial investment cost. In addition, the system software can be cumbersome and difficult for the casual user to operate, often requiring days of training for the operator to become familiar with even the simplest of experiments. All of these items have restricted the use of microscopy and imaging systems to research laboratories, with very limited access by the standard analytical laboratory.
Upgradeable FTIR microscope platform
In the past, FTIR microscopes and imaging systems have been the realm of research laboratories or users with extensive experience in infrared spectroscopy. The less experienced user may have been intimidated by the cost and requirements for FTIR microscopy, avoiding the use of an FTIR microscope. However, with the ability to integrate an FTIR microscope to even the lowest-level FTIR instrument, the IRT-5000/7000 series (JASCO, Easton, MD) brings FTIR microscopy within the reach of even the casual user. The decreased cost of ownership allows users of any capability access to an FTIR microscope, and the software interface also provides simplicity of operation as well as advanced capabilities for imaging applications. By designing an FTIR microscope system that is functionally upgradeable and is able to accommodate the needs of all types of users, the IRT-5000/7000 series can provide only those capabilities desired at the time of purchase, but also offer extended capabilities as the needs of the laboratory grow.
The IRT-5000 FTIR microscope system, in the most basic configuration, can be obtained with a manual stage and a single-element mercury cadmium telluride (MCT) detector. Options include 10×, 16×, or 32× cassegrain objectives for reflection and transmission experiments; 10× or 20× refractive objectives for sample visualization; a grazing-angle cassegrain for thin films on reflective substrates; and a suite of attenuated total reflectance (ATR) objectives—including ZnSe, Ge, and diamond ATR crystals—for otherwise intractable samples. With the ability to incorporate up to four objectives as well as interchangeable cassegrains and ATR objectives, the IRT-5000/7000 series can support a wide range of sample visualization and data collection capabilities. Other options include differential interference contrast capability, visible and infrared polarizers, and a fluorescence sample observation capability. The IRT-5000 can be upgraded at any time with an XYZ autostage for mapping experiments as well as a multielement linear array detector for imaging experiments.
Figure 1 - IRT-7000 FTIR microscope imaging system attached to a JASCO FT/IR-6100 instrument.
Alternatively, the IRT-7000 (Figure 1) is an imaging system that incorporates both the single-element MCT and multielement linear array detectors with an XYZ autostage. The single-element MCT detector on either system can also be specified as user-interchangeable, providing the ability to exchange the single-element MCT detector for other spectral range detectors such as an InGaAs or InSb for near- infrared (NIR) experiments, or even a deuterated triglycine sulfate (DTGS) detector for use without liquid nitrogen but with an extended mid-IR spectral range. These options can be added to the microscope system at any time, enabling the user to extend the capabilities of the microscope accessory to imaging or other applications when desired by the analytical laboratory.
Figure 2 - Infrared microscope data collection software dialog.
The IRT-5000/7000 microscope software is a user-friendly graphical interface with “point-and-click” options for single-spectrum or multipoint collection as well as line and grid-mapping applications (Figure 2). The IQ Monitoring function incorporates a charge-coupled device (CCD) video camera that can record single- or multielement video capture pictures of the sample area and storage in a thumbnail display area for instant retrieval by the user. When a sample area is specified for data collection, a video image of that area, no matter the size, is automatically captured for storage with the data file and later display in the microscope data analysis software. The IQ Monitoring software also provides features for the autoillumination of the sample area and autofocusing of the sample for data collection when using the XYZ autostage.
An optical zoom mode provided within the tabbed microscope parameters display can offer a range of 0.6–2× magnification of the video image; a digital magnification of the video display from 50 to 500% is selected by right-clicking the displayed image. Instrument collection parameters and microscope operations such as optical zoom mode are immediately accessible within a tabbed display in the main software dialog, and are not hidden within multiple menus and commands, providing the user with instantaneous access to items such as microscope aperture size, objective selection, polarizer selection, scan accumulation, and resolution selections, while allowing items to be changed as required for the immediate experiment. Utilizing a dichroic mirror, the sample video image is simultaneously displayed during data collection; spectral data and/or image maps are also actively updated during data collection and imaging experiments, supplying up-to-date information for the user during the experiment.