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The Infrared Spectroscopic Determination of Moisture in HCl for the Characterization of HCl Gas Drying Resin Performance

A Fourier transform infrared spectroscopic method has been developed for the determination of trace moisture in HCl gas. Calibration of moisture was performed as a two-step process. First, an FT-IR spectrometer equipped with a 10-m-pathlength cell was placed in series with a DuPont 5700 Moisture Analzyer to yield an absorbance vs. concentration curve of H2O in N2. In the second step, the moisture analyzer was replaced with a water scrubber, and the correlation of molar absorbance values for moisture in HCl vs. moisture in N2 was obtained through dilution of a fixed-concentration moist nitrogen stream into alternate streams of dry HCl and N2 gas. The effects of hydrogen bonding with the HCl matrix on H2O absorbance bandwidth and intensity were investigated at 2 cm−1 and 0.5 cm−1 spectral resolutions for the O-H stretching absorbance region. Matrix correlation data resulted in a linear calibration of moisture in HCl gas for the 0.1–25 ppm range. The infrared methodology has been further utilized to characterize the performance of several HCl gas purifiers designed for use in semiconductor applications. The in-line configuration of this method permits direct quantitation of HCl gas dryer efficiency, capacity, and flow rate specifications. Instrumental considerations including corrosion-resistant optics, inert seals, fittings, valves, purge techniques, and calibration procedure details and results are discussed.