Anal. Chem. 1988, 58,1903-1904 (2) Nygren, S.;Anderson, S. Anal. Chem. 1985, 5 7 , 2748-2751. (3) Arnold, A. P.; Dalgnautt. S. A,; Rabenstein, D. L. Anal. Chem. 1985, 5 7 , 1112-1116. (4) Gampp, H.; Maeder, M.; Zuberbuhler, A. D.; Kaden, T. A. Tabnta 1980, 2 7 , 513-518. (5) Stradling, R. S.; Ryan, P. A.; Wood, J. D. Comput. Enhanced SpecWOSC.1983, 1 , 25-30. (6) Wong, C. M.; Crawford, R. W.; Kunz, J. C.; Kehler, T. P. I€€€ Trans. N u c ~ SCl. . 1984, 3 1 , 805-810. (7) White, R. L. Compot. Enhanced Spectrosc. 1988, 3 , 35-40.
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(8) Koval, C. A.; Rutkowskl, C. J.; Cowan, J. P. Anal. Chem. 1985, 5 7 , 1163-1 165. (9) Seyer, M. D. RS-232 Made Easy: Conmting Computers, Prlnters, Terminals, and Modems; Prentlce-Hall: Englewood Cliffs, NJ, 1984. (IO) Microelectronics Data Catalog; General Instrument Corp.: Hlcksville, NY, 1982.
RECEIVED for review February 21,1986. Accepted April 14, 1986.
Determination of Water in Hydrogen Chlorlde Gas by a Condensation Technique Edward Flaherty, Christopher Herold, and Donald Murray Matheson Gas Products, Inc.,932 Paterson Plank Road, East Rutherford, New Jersey 07073
Scott R. Thompson* Matheson Gas Products, Inc.,6775 Central Avenue, Newark, California 94560 The determination of trace amounts of water in gaseous hydrogen chloride has been of considerable interest to manufacturers of semiconductor materials. Many different methods have been postulated in the detection of water in hydrogen chloride, including Karl Fischer titrations (I-3), infrared spectrometric techniques ( 4 ) , and gravimetric procedures using desiccants (5). Despite varying degrees of succe9s at high-moisture concentration ranges, lo00 ppm (v/v) and up, these methods become tedious and unreliable for measuring water in hydrogen chloride in the 1-1000 ppm range. We have found a method for moisture in hydrogen chloride, analogous to dew point determinations used for inert gases, that is rapid and reproducible. A calibration curve of parts per million (v/v) water in hydrogen chloride vs. condensation temperature was constructed by dynamically blending a low part per million moisture balance nitrogen standard with dried hydrogen chloride gas. In addition, variation of the condensation temperature was monitored as the dried hydrogen chloride was diluted with dried gaseous nitrogen.
EXPERIMENTAL SECTION Apparatus. A dew point detector was obtained from the Hamada Electric Works, Ltd.(Tokyo, Japan), and is designated a Hads dewpoint indicator. Corrosion-resistant fluorocarbon resin is used as the body of the detection cylinder, with a platinum mirror at one end and a quartz viewing window at the other. Temperature monitoring of the platinum mirror is done by using a copper constantan thermocouple attached to the back of the mirror. Cooling is provided by a stream of nitrogen that has been passed through a liquid nitrogen heat exchanger directed to the point of attachment of the thermocouple and the mirror. This method allows the mirror to cool and warm rapidly. Sample exhaust from the dew point detector is vented at atmospheric pressure to a caustic scrubber. Mixing of the water balance nitrogen standard with the dried hydrogen chloride gas stream was done with a 316 stainless-steel gas proportioner (Matheson, Model 7372T) equipped with calibrated rotameter tubes (Matheson: no. 600 for water balance nitrogen, no. 603 for hydrogen chloride). The rotameter tubes were calibrated for the individual gases to a delivery pressure of 20 psig and an accuracy of 5%. All plumbing was done by using 1/8-in.-o.d. 316 stainless-steel tubing and Swagelok connectors. A schematic of the apparatus is shown in Figure 1. Reagents. Hydrogen chloride used in the experiment was stock Matheson Gas Products' semiconductor purity. Three water balance nitrogen standards were prepared at concentrations of 40,200, and lo00 ppm (v/v) water with nitrogen (Matheson UHP grade) as the balance gas. These standards were verified with an electrolytic cell (Beckman Instruments), aluminum oxide sensor 0003-2700/86/0358-1903$01.50/0
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TO CAUSTIC SCRUBBER
DEWAR HYDROGEN CHLORIDE
Figure 1. Schematic of apparatus used to collect data for the cali-
bration curve. (Shaw Instruments), dew point techniques, and chromatographic determination of acetylene evolved by contacting the gaseous water standard with calcium carbide. Desiccants used to dry the hydrogen chloirde gas stream were packed into 12-in. X 1/2-in.diameter stainless-steel pipe and treated as follows: magnesium perchlorate (VWR), used as received; silica gel (8 mesh, Aldrich) and molecular sieves (3A, 4A, 5A; Union Carbide); desiccant-filled traps were heated at 200 "C while under a vacuum of less than 1 mmHg for 6-8 h. Procedure. The dew point detector is kept under constant purge using nitrogen predried by flowing through a phosphorus pentoxide moisture trap. The lower limit of the temperature monitoring range is -90 "C, and when no condensation from the nitrogen purge is detected at this temperature, the sample system and detection cell have dried sufficiently. Typical determinations of the condensation temperature of a hydrogen chloride sample require 30 min with the sample flowing at a rate of 1 L/min. Fifteen minutes after hydrogen chloride flow has been established, a determination of the temperature at which condensation develops is made and immediately repeated. At temperatures less than 0 "C the condensation appears as a fine white solid occluding the reflectivity of the mirror; temperatures above 0 "C may also have formation of liquid droplets in the condensation. The determination of the condensation temperature is repeated every 15 min until two successive determinations are within 1 ' C . Calibration curve data were collected in the same manner, using a total sample flow rate of 1 L/min to calculate individual component flow rates. The hydrogen chloride gas stream was dried by installation of the desiccant bed in line between the gas cylinder and gas proportioner. To determine if the desiccant bed is working, no condensation should appear before the condensation of hydrogen chloride, visible as a clear puddle of liquid on the 0 1986 American Chemical Society
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ANALYTICAL CHEMISTRY, VOL.
58, NO. 8, JULY 1986
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Flgwe 2. Effect of varying background concentrations of hydrogen chloride and nitrogen on the condensation temperature while holding the moisture concentration constant at 11 ppm (v/v).
Figure 3. (1)Moisture in hydrogen chloride;graph represents equation y = (in ( x / A ) ) / B ,y = condensation temperature, x = parts per million water added, A = 830, B = 0.14, coefficient of correlation ( r ) = 0.9530. (2) Moisture in inert gases derived from the vapor pressure
mirror with a corresponding temperature of approximately -85 "C at atmospheric pressure.
of water over ice, total pressure assumed to be 101.3 kPa.
RESULTS AND DISCUSSION Addition of the water balance nitrogen standard to the dried hydrogen chloride gas stream diluted the background of hydrogen chloride and presented a possible source of error in the calibration curve data. We originally kept this dilution at a maximum of 15% added nitrogen to minimize any error; we were later able to add another dried gaseous nitrogen source to the system and vary the background levels of nitrogen and hydrogen chloride while holding the moisture level constant. Figure 2 illustrates the behavior of the condensation point as the background matrix was varied from 100% nitrogen to 9O:lO hydrogen chloride/nitrogen while the amount of water was held constant at 11ppm (v/v). Dilution only becomes a factor when the nitrogen content exceeds 50% of the background matrix. This behavior is an example of the interactive forces betwen water and hydrogen chloride, which has been a major problem in the determination of water in hydrogen chloride. Another example is seen in the direct comparison of the calibration curve obtained in this work against a curve constructed by using the vapor pressure of water over ice (6),which is used for dew point determinations of water in inert gases, illustrated in Figure 3. Fifty data points of parts per million water in hydrogen chloride vs. condensation temperature were used to fit a logarithmic equation using the method of least squares. Errors for the concentration of added moisture in hydrogen chloride are estimated at 10% of a given value based upon flow meter error, water balance nitrogen standard preparation error, and atmospheric pressure fluctuations over the course of data collection. Significant reduction in error could be made by using mass flow controllers in all gas stream mixing. The difference in the two curves obtained is a displacement in the y axis of
approximately 30 "C, or, for a given amount of water, the condensation temperature in a hydrogen chloride background is 30 "C higher than the condensation temperature in an inert (argon, nitrogen, helium, etc.) background. We originally suspected that the condensation observed was not uncomplexed water, but some hydrated specie of hydrogen chloride. The evidence found here supports our suspicion and indicates that free water may not exist in a hydrogen chloride matrix; hence we have avoided the term "dew point" when referring to water in hydrogen chloride. In conclusion, we assert that the observed condensation temperatures are directly related to the moisture concentration of gaseous hydrogen chloride, and the deviations between this empirically derived calibration curve and curves constructed using the vapor pressure of ice or water are easily rationalized by the interactive force between hydrogen chloride and water. This evidence is supported by the findings of Shatalov and Levinskii (7) concerning condensation temperatures of water at percentage levels in hydrogen chloride. Registry No. H20, 7732-18-5; HCl, 7647-01-0.
LITERATURE CITED (1) Beider, T. B. Zavod. Lab. 1965, 3 1 , 1327. (2) Milberaw. E. D.: Uhria, K.: Becker, H. C.; Levin, H. Anal. Chem. 1949, 21. i i w - 1 1 9 4 . Kaname, M.; Mitsumasa, 0. Mlcrochem. J. 1973, 78, 234-239. J. Chem. SOC.,Faraday Trans. 1975, 69(11), 1628. Encyclopedia of Industrial Chemical Analysis; Snell, F. D., Hilton, C. L., Eds.; Interscience: New York, 1966-1970; 20-volume series. Goff, J. A.; Gratch, S. Trans. Am. SOC.Heat. Vent. Eng. 1946, 52, 95- 122. Shatalov, B. I.: Levinskii, M. I. Zavod. Lab. 1969, 35(3),383-364.
RECEIVED for review December 11,1985. Accepted February 27, 1986.
