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Detection of Moisture in Ammonia Gas

Problem Statement

As technologies advance, so does the request for ultra high purity ammonia. Ultra high purity (UHP) ammonia is used in the semiconductor industries, production of flat panel displays, and a number of other applications. Due to this rising interest in UHP ammonia, manufacturers are having to battle ammonia's most prominent and damaging impurity--moisture. For these applications to work properly it is critical that the moisture levels be as low as possible in the ammonia. As a result, there is a great need for an ammonia gas analyzer that can measure low levels of moisture as an impurity.

IRGAS Applicability

The IRGAS-EPI/Hx™ is the newest addition to CIC Photonics' IRGAS™ (Integrated Realtime Gas Analysis Solution) product line. This analytical tool is designed to measure moisture impurities in ammonia gas down to the 10-15 ppb range. The IRGAS-EPI/Hx™ is optimal for moisture in ammonia analysis because of the combination of a FTIR spectrometer that utilizes a TE-Cooled InAs detector and a long path gas cell. This detector is preferable for moisture analysis because of its high sensitivity capabilities and its wavenumber range of 3000-7000 cm-1. CIC Photonics' Ranger-ENTM long path gas cell (9.6-meters) completes the system design by incorporating stainless steel body and mirrors, proprietary multi-layer gold coatings, and a plenum-type laminar gas flow. Combining all of these features with the sophisticated softwares, SPGAS™ and SpectraStream™, creates a high-senstivity analytical solution to the moisture in ammonia requirement.

IRGAS System Description

The IRGAS-EPI/Hx™ spectrometer is a rugged Bomem WorkIR (FTPA2000) spectrometer that uses a TE-Cooled InAs detector. Included is a power supply specifically for the TE-Cooled detector to provide for easy usage, unlike the liquid nitrogen detectors that require monitoring and refilling. Mounted on top of the spectrometer is the 9.6m Ranger-EN long path gas cell. The gas cell is also equipped with heaters and a permeation-isolation box that surrounds the gas cell and optical couplers in order to prevent condensation. The SPGAS™ software uses a weighted, multiband, multilevel, multivariate classical least squares method to determine the concentrations of the components in the sample. In addition, the SPGAS™ software can be used to manage the system's hardware, such as valves, regulators, sensors, and pumps. The software program SpectraStream™ is designed to provide a fast-response indicator of changes in gas concentrations. Both of the software programs are highly user-friendly regardless of experience level.

Solution Achieved

To the left are three FTIR data graphs, which show the IRGAS-EPI/Hx™ results to the moisture in ammonia analysis. Figure 1 demonstrates the system's ability to detect moisture as it was being used to test a SAES Getters ammonia purifier. As the ammonia purifier is being bypassed, the system showed an increase in the moisture levels; once the purifier was back inline, the system indicated the moisture levels dropping. Shown in Figure 2 is the rapid response of the instrument as the moisture is withdrawn from the sample; and Figure 3 displays an absence of moisture in ammonia over a 30-minute period.

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