Anal. Chem. 1082, 5 4 , 2627-2628
2627
Determination of Water in Hydrogen Bromide Gas
'
Robert Welntraub" and Alexander Apelblat' Bromine Compounds Ltd., Beer Sheva, Israel
The moisture content of HBr gas was found to be needed during the course of corrosion studies. No published results were found by the prerrent investigators concerning an analytical method. Karl Fischer titrations cannot directly be used in this case due to the extreme reactivity and corrosivity of HBr gas. The analytical method described here involves the reaction of HBr gas with excess pyridine to form the C6H6N.HBrsalt. The HBr is quickly removed from the reaction by precipitation of this salt. The mixture which contains both excess pyridine and the precipitated salt is titrated with Marl Fischer reagent to determine the water content.
EXPERIMENTAL SECTION Sample Cell. A Karl Fischer cell has been employed which enables HBr gas to flow into it and react with pyridine. The unique design of the cell enables the solid pyridine salt to be formed by avoiding the common problem of clogged connections. The cell contains an internal funnel which extends from one of the openings almost to the bottom of the cell. The details of this three-mouth cell are shown in Figure 1. Due to the pyridine level being higher than the level of the bottom of the internal funnel, no HBr can escape to the atmosphere without having to first pass through the pyridine. Three gound glass joints are provided. During the collection of the HBr sample, one fitting contains a drying tube with alumina, one an inlet tube for HBr gas, and the other a ground glass stopper. During the Karl Fischer titration, the three joints contain desiccant, the Karl Fischeir reagent inlet, and the electrode. Procedure. About 60 mL of dried pyridine is transferred from a closed bottle to a dried cell, all the time excluding any contact with the air outside. This was performed by storing the pyridine in a Karl Fischer titration reagent bottle from Metrohm and using the Multi-Dosimat E415 for all transfers. The cell is prepared by first washing with water, rinsing with acetone, and allowing it to dry overnight at over 100 "C in an oven. The cell is subsequently cooled while exposed to a stream of dried Nz gas. HBr (supplied by Matheson Gas Products) is allowed to flow into the cell containing the pyridine. The cell is cooled by an ice-water bath. Stirring is effected inside the sample cell by means of a Teflon magnetic stirring bar during sample collection. After a sample of about 4-6 g hias been collected, the cell is stoppered, weighed, and transferred to a Metrohm titrator. The Karl Fischer reagent is the commerciallly available Merck Reagent with a factor of about 0.00526 g of water/mL of reagent. After the end point is signaled on the titrator, the cell is shaken to dislodge any materials adhering to the walls. After the cell was shaken, the sample is again titrated t o the end point. This procedure is repeated three times in order to ensure attainment of the true end point. Tests for unreacted HBr gas present in the reaction vessel, by means by watching for the formation of white fumes with ammonia, always proved negative. The water content of the pyridine is determined with the same quantity of pyridine as that employed in the collection of HBr. It was desirable to keep the technique for the titration of the pyridine as similar as possible as to the titration of the HBr sample. Therefore, the end point for the pure pyridine was located three times successively, with mixing of the cell between titrations. The water content of the pyridine was found to be independent of the presence of pretitrated methanol. Microliter calibrated syringes were used to add a known volume of water to the glass section of the cell leading from the gas cylinder to the cell (see Figure 1). This section of glass tubing was heated by a heating fan during the course of the HBr flow to evaporate Present address: Department of Chemical Engineering, Ben Gurion University of the Negev, Beer Sheva, Israel. 0003-2700/82/0354-2627$0 1.25/0
Table I. Results of Analysis of Samples with a Known Amount of Water Addeda run 1 2 3 4 5 6 7 8 9 10 l l b
12b 13 14 15 16 17 18 19b 20b 21 22
g of HBr collected 3.75 3.76 4.00 4.24 4.61 4.64 5.19 5.32 5.40 5.84 7.50 4.67 7.96 6.30 5.89 5.54 4.80 4.65 2.80 1.67 4.97 2.01
ppm of H,O added found 0 0 0 0 0 0 0 0 0 0 133 214 628 794 84 9 903 1042 1075 1286 1856 201 2 2537
260
-7 70 32 78 96 1 12 32 -125 - 70 126 623 820 690 1047 1041 929 1071 1904 2086 2664
a The volume of pyridine employed was from 61.13 to 61.21 mL. The volume of Karl Fischer reagent varied from 3.8 to 5.5 mL. See text.
Table 11. Analysis of Wet HBr Gas at Room Temperature after Being Bubbled through a Saturated H,O-HBr Solution of 8 cm Height sample size, g of HBr
ppm of H,O in HBr
4.85 3.49 4.65
280 660 3 50
the moisture. The heating was kept on until all the water had evaporated into the gas stream as determined by visual observation. A white film attributed to a C6H6N.HBrlayer remained after heating. The loss of water due to incomplete vaporization was not a factor since any water that failed to vaporize remained in the cell. Several trials were run whereby the water was added to the inlet tube leading to the cell. This meant that incomplete vaporization would lead to a low result. This was not observed. These trials are indicated with a superscript b in Table I. Corrosion and moisture buildup in the gas outlet valve of the cylinder were of concern. In order to keep these phenomena to a minimum, we dried the valve of the HBr gas cylinder several hours with dry nitrogen before and after each use. Moisture buildup in the HBr cylinder was suspected as being a source of error in the analysis. When HBr gas was passed through the cylinder valve for about 10 min before collecting the sample, however, no change in accuracy was observed.
RESULTS AND DISCUSSION The results of the analysis of known samples are summarized in Table I. The average error for the analysis is found to be less than 100 ppm, corresponding to approximately 0.0004 g water for a 5 g sample. The negative numbers in the 0 1982 Amerlcan Chemical Society
Anal. Cham. 1962. 54. 2628-2629
2620
without additional water added to them were not wet enough to he sensitive within the limits of error to confirm or deny the presence of water. The samples shown in Table I1 were prepared hy huhhling HBr gas through a saturated H,O.HBr solution of 8 cm depth, a t room temperature. The gas was then passed through an empty trap and then was analyzed for water content. The results are shown for the analysis, performed three times. In looking a t these results, i t must he remembered that no attempt was made to achieve reproducible conditions between experiments in relation to attainment of isothermal equilibrium between the phases. However, the moisture content of this “wet” HBr gas can he considered as a rough approximation to the equilibrium value. It is clear that the Matheson HBr gas is not a “wet” gas as it leaves the cylinder as compared to the HBr stream analyzed after passing through the water (see results of samples numbered 1through 10 on Table I and compare with those in Table 11).
I
ACKNOWLEDGMENT
npure 1. Sample cell.
column =ppm of H,O found” in Table I have the meaning that less water was found in the sample than was determined to be present in the pyridine itself. These negative numbers are due to random experimental error. The samples analyzed
The authors wish to thank M. Dariel, former Director of the Research Division of Bromine Compounds Ltd.,for suggesting this topic and constant encouragement. We are indebted to Chaim Amit, the present Director of the Research Division, for permission to publish this work. The fine technical assistance of Z. Tannenhaum is greatly appreciated. The entire staff of the Research Division is noted for their willingness to share their experience and for technical assistance whenever needed. REcEnm, for renew March 2,1982. Accepted August 16,1982.
Glass and Teflon Closed-Loop Pumping System for Ultraviolet Absorbance Measurements Dennis R. MlgneauH and R. Ken Forci’ D8pariment of chemistry, University of Rhode wand, Kingston. Rhode Island 02881
Frequently the simultaneous acquisition of ultranolet absorhance spectra along with the measurement of some other parameter such as electrode potentials is desirable during the course of an experiment. Also, in order that solution experimental conditions be maintained the same for both measuring processes, a closed-loop system with pumping is frequently the optimum situation. In addition, since ultraviolet absorbance measurements in long path cells are very sensitive to trace levels of contaminants, the design of the system must be such that the construction materials are inert and, if adsorption of trace element contaminants be possihly suspected, the system must he available for the proper cleaning procedures such as acid leaching. Many commercially available pumps contain a variety of2ifferent types of plastic components, and many of these components are in contact with the working solution. Ultraviolet absorbing plasticizers and contaminants, under mildly acidic conditions, can frequently he leached from these plastics and into the solution. Of a simple flow-through system We report here the connecting a Cary Model 210 ultraviolet-nsihle spectrophotometer with a potentiometric experiment. The apparatus was designed with the following criteria in mind (1)materials of construction do not contaminate the solution of interest,
(2) the mixing time for the whole system he minimal, (3) the installation of the apparatus and the removal from the Cary he simple and quickly accomplished, and (4) constant temperature in the solution he maintained.
EXPERIMENTAL SECTION The instrumentation used is the Cary 210 spectrophotometer with 10-cm fused silica cells. The electrodes employed were a Coming m p l e Purpose pH electrode with either a doublejunction SCE or double junction Ag/AgCI reference electrode. The double junction was filled with 4.0 M NaNO, in a viscous aqueous carbohydrate medium, The electrode potentials were monitored hy a Commodore PET Model 2001 mimmmputer with the necessary analog and digital interfacing as described elsewhere (1). The potentiometric cell was therkostated from a 50-L water bath controlled by a Haake water heater and pumped through coils surrounding the IeaCtion The design of the pump is simple and straightforward (Figure 1,, A 4,2-cm hole was through the bottom of a Pyrex beaker and a Pyrex petri dish of approximately the same size was attached to the bottom of the beaker by the chemistry department glassblower. An 8 mm 0.d. Pyrex glass tube was attached tangentidy to the side of the petri dish to provide egrw for the solution. A ret- tube f ” the spectrophotometer comea over the top edge of the beaker and hack into the solution. A
ooo3-27ool82io35c282s~Ol.2SlO 0 1982 American Chnmknl Socishl
