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MID–IR PROCESS SAMPLING ACCESSORIES
Axiom Analytical pioneered the field of mid–IR liquid analysis with the development of the first ATR immersions probes.1, 2, 3 This was quickly followed by the development of the first photometrically accurate ATR flow cells,4, 5 the first linear flow gas cells,6 and the Axiot System of modular optical transfer and multiplexing equipment.7 These developments, along with subsequent pioneering work in such areas as diamond–tipped ATR probes,8, 9 and solid sampling10 have enabled Axiom to remain at the forefront of both laboratory and process analysis using mid–infrared spectroscopy.
A summary of Axiom’s mid–IR product line appropriate for process analysis is provided below. To jump to specific sections of the list, click on the following categories:
A. PROCESS MID–IR ATR PROBES AND CELLS
ATR makes mid–infrared liquid analysis possible. The absorptions corresponding to the fundamental vibrations of most organic chemical fall in the mid–infrared region of the spectrum. However, most of these absorptions are far too strong for practical transmission analysis. ATR solves this problem by providing very short effective pathlengths.11, 12 Axiom Analytical has pioneered the application of ATR to a wide range of tasks both in the lab and on the process line.13, 14 The company’s process ATR product lines are summarized below. Additional ATR probes are included in the Lab–Line section of this website.
1. High Transmission ATR Probes
DPR–240 and DMD–370 ATR probes1,2,3 employ dual internal lightguides, one to conduct IR radiation to the ATR element and one to return the radiation to the instrument. This arrangement provides the highest possible signal level, an important factor for process applications where it is often not possible to use a liquid nitrogen cooled (high sensitivity) IR detector. These probes share the high performance characteristics of the Company’s laboratory ATR probes, including a high degree of repeatability and photometric accuracy.15
DPR–240 AND DMD–370
- High sensitivity without requiring cooled detector
- Diamond element for excellent corrosion resistance (DMD)
- Interchangeable ATR elements to meet diverse needs (DPR)
- Proprietary optical designs for maximum photometric accuracy
- Robust construction for maximum reliability
Axiom’s TNL Series "TUNNEL" ATR flow cells4,5 set the standard for highly accurate, yet economical, mid–IR liquid analysis. The patented design of these cells insures that all optical rays passing through the cell experience the same number of reflections and nearly the same angle. This results in a very high degree of photometric accuracy and repeatability.13 In addition, the helical flow characteristics insure rapid sample exchange and cleanout.5
TNL SERIES
- Rugged, adjustment–free design
- Cylindrical elements for optimum flow characteristics
- Absolute repeatability
- High sensitivity
- Rapid sample clean out
- High transmission
B. PROCESS MID–IR GAS AND LIQUID TRANSMISSION
For decades, most IR gas analysis has been carried out using the traditional “White cell” design. This provides a compact size but poor flow characteristics and hence is troubled by sample carryover. Axiom has pioneered the use of a linear flow approach in which the optical and flow paths are identical. The result is very rapid sample exchange with no carryover.11
LFT Series cells can be mounted either in a spectrometer’s sample compartment or outboard by means of the Axiot System of optical transfer assemblies. The extremely low volume, fast response, and fixed optical paths of these cells make them ideal for the dynamic analysis of rapidly changing gas concentrations.
LFT SERIES
- Convenient sample compartment mounting
- Very low volume
- Fast response with negligible sample carryover
- Path lengths to 2 meters
- Easy maintenance
2. Long Path, Corrosion Resistant Cells
Axiom’s linear flow gas cells6 offer the highest optical stability and fastest response to changes in sample composition of any gas cell of comparable pathlength. LFG cells have demonstrated significantly higher performance compared to multi–pass or “White cell” designs. The advantage lies in the use of a tubular flow path which exactly overlaps the IR beam. This yields plug flow conditions, allowing a complete exchange of sample gas within seconds.11 The extremely fast response of this design, combined with rugged optics which never require adjustment, make LFG cells the clear choice for intermediate path industrial gas analysis.
LFG SERIES
- Linear flow for fast response
- Pathlengths from 10 cm to 16 meters
- Axiot coupling to most spectrometers
- Choice of windows, seals, and materials of construction
3. High Pressure Short Path Cells
The extremely rugged and reliable LFC Series transmission cells are appropriate for the analysis of high pressure gasses as well as relatively non–absorbing condensed phase materials such as liquid Chlorine. These cells are available in both sample compartment and outboard configurations and are suitable for both research and process applications.
LFC SERIES
- Suitable for inboard or outboard use
- Pressure ratings to 65 bar
- Standard pathlengths of 3 and 10 cm
C. PROCESS MID–IR SOLIDS ANALYSIS
The mid-infrared analysis of solids presents some unique challenges. These result from the fact that the fundamental absorptions which fall in the mid–IR are far too strong to allow either transmission or diffuse reflectance analysis of intact bulk samples. There are three general approaches to dealing with this problem. First, if the sample is available in powder form, it can be mixed with a non-absorbing powder such as KBr and either pressed into a pellet for transmission analysis or analyzed directly using diffuse reflectance. Second, many samples can be analyzed directly by using specular reflectance10, 16. Finally, samples that can be extruded as films, or which are already available as films, can often be analyzed in transmission.
Over the years, Axiom has developed a number of sampling systems for analyzing solids in all three forms: bulk solids, powders, and thin films. At present, these are all handled as custom applications of the Axiot System. In addition, specific sample compartment mounted sampling accessories are currently in development. Please inquire with Axiom regarding product descriptions and availability.
Call Axiom for Hardcopy of Technical Note AN–908
Return to topD. PROCESS MID–IR AXIOT OPTICAL TRANSFER AND INTEGRATED SYSTEMS
The Axiot System7 is a family of optical transfer and sampling modules which can greatly expand the sampling flexibility of virtually any infrared spectrometer. By removing the sampling task from the confines of the conventional sample compartment, the Axiot System eliminates performance compromise while allowing an analysis to be carried out at the most desirable location such as in a fume hood or on a process line. In addition, the modular components of the Axiot System can be used to configure custom sampling systems to meet the requirements of almost any analysis.17, 18 Finally, the system has enabled Axiom to develop comprehensive systems in which spectrometers are integrated with the appropriated sampling devices, enclosures, and other sample conditioning and monitoring equipment.
THE AXIOT SYSTEM
- Interfaces spectrometers to separated sampling equipment
- Facilitates system integration
- High transmission efficiency
- Compatible with virtually all sample techniques
- Efficient purging for maximum sample throughput
- Eliminates the risk of instrument damage due to sample spill
- Allows analysis to remain set–up while free FTIR sample compartment for other tasks
REFERENCES
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