Consistent quality and supply of purge gas is critical for the proper operation of an FTIR spectrometer. Using an in-house gas generator is the most reliable, safest and most economical method for obtaining purge gas for your FTIR spectrometer.
An FTIR spectrometer is an instrument that measures the infrared spectrum of a sample. All elements and compounds that absorb infrared energy do so uniquely, like a fingerprint. Thus, by measuring the absorbance of a sample across the infrared spectrum, it is possible to fingerprint the sample. This fingerprint is compared to a library of known spectra and the unknown sample is easily identified. An FTIR spectrometer is normally used as a qualitative tool to identify which elements and compounds make up a sample, but it may also be used as a quantitative tool to determine amounts of elements and compounds in the sample. Common applications include identifying drugs and experimental compounds and verifying incoming feedstocks and outgoing products.
The optics inside the FTIR spectrometer are finely polished lenses made of, or coated with, hygroscopic (water absorbing) salts such as potassium bromide (KBr). These salts are used instead of glass because they do not absorb infrared radiation, as glass does. If the optics are exposed to even minute amounts of water vapor, they will fog. Exposure to water or water vapor causes the KBr to dissolve, ruining the finely polished surface. Resolution of the instrument will slowly deteriorate requiring replacement of the optics, which can be very costly.
The presence of water and carbon dioxide in the path of the infrared beam causes unwanted noise in the infrared spectrum. Purging the FTIR spectrometer with clean, dry carbon dioxide-free gas will improve the signal to noise ratio (SNR) by decreasing the level of background noise.
Read this study on the effect of purging a sealed and desiccated FTIR spectrometer sample compartment
Nitrogen cylinders used in conjunction with a desiccator.
An in-house purge gas generator that ports purge gas directly to the FTIR spectrometer.
Although cylinders are commonly used, they have several disadvantages:
An in-house purge gas generator produces dry, CO2 free air from compressed air using a combination of coalescing filtration and pressure swing absorption (PSA) technologies. A coalescing filter removes particulate matter such as dust, pump oil and water particles. The PSA system contains molecular sieves to remove CO2 and water vapor. Parker FT-IR Purge Gas Systems are available to provide up to 216 scfh (102 lpm) of purge gas.
An in-house purge gas generator provides the following benefits:
Greater Safety - A small amount of gas is present at low pressure and is ported directly to the spectrometer. Whereas, a gas tank can explode if the valve is compromised, leading to the possibility of injury or property damage during transportation and installation.
Convenience - An in-house generator operates on a continuous basis without user interaction. In contrast, when a cylinder is employed, the user must pay close attention to the level of gas in the tank and replace it as necessary. FTIR systems that include a desiccant to eliminate water vapor from the sample compartment require that its condition be monitored, so if the tank is exhausted, important data may be lost if the FTIR is collecting data on an unattended basis.
Lower Cost - The cost of operation of an in-house gas generator is extremely low when compared to the cost of ordering, transporting, storing, and handling high pressure gas cylinders. Aside from the initial purchase, the only cost associated with operation of an in-house gas generator is electricity. The payback for an in-house gas generation system is typically one year or less.
Environmental Benefits - The energy requirements for an in-house purge gas generator are quite low. When cylinders are used, the gas must be purified and compressed to 2000 psi. Once the tanks are filled, they must be transported to the end user’s site and the empty tanks must be returned to the supplier. All of this activity expends unnecessary energy.
For additional information, read this study on the effect of purging a sealed and desiccated FTIR spectrometer sample compartment
This post was contributed by the Gas Generation technology blog team, Parker Hannifin.