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Anal. Chem. 1982, 5 4 , 340-342
Flgure 1. Dlagram of modified flanglng tool: (a) flanging tip, (b) cooling plate, (c) flanger base, (d) ring stand support, (e) Tlrrill burner.
of a high-wattage power resistor which provides the heat when connected to a 110-V ac source. This assembly is then mounted in a small metal cabinet. Unfortunately, such devices are rather slow to warm up (-45 min) and are not very effective once their peak temperature is reached, especially with thick-walled tubing. An easily executed, though extensive modification of a typical commercially available device can increase its operating efficiency dramatically. The commercial device is stripped of all electrical compo-
nents, and only the heavy base and flanging tip are retained. A short length of aluminum rod and standard laboratory hardware are used to bolt the base to a titration stand. A standard Tirrill burner is used as a heat source. The completed device is shown in Figure 1. The flanges produced, even with thick-walled tubing, are superior to the resistively heated unit in both size and uniformity. This design allows one to achieve a warm-up time of about 5 min and to attain a wide range of temperatures with good temperature control. Obviously, one of these units could be easily built from scratch if an electrical unit was not available for modification. The flanger tips are available as separate items from the companies which supply the entire device. This converted device has been in use in our laboratory for over a year with no operational difficulties. Though it is too large to be used in the close confines of an instrument, its size is not usually a problem, as most tubing can be removed from an instrument in order to work on it.
RECEIVED for review September 14,1981. Accepted October 19,1981. Operated for the U. S. Department of Energy by Iowa State University under Contract No. W-7405-ENG-82. This research was supported by the Director of Energy Research, Office of Basic Energy Sciences.
Analysis of Chloride-Doped Cadmium Sulfide by Ion Chromatography William F. Koch" and Jeffrey W. Stolz Center for Analytical Chemistty, Natlonal Bureau of Standards, Washington, D.C. 20234
Cadmium sulfide, doped with various elements, has been used extensively in the photoconductor and solar energy industries (1-4). Recently there has been renewed interest in cadmium sulfide doped with cadmium chloride for use as a possible superconductor at noncryogenic temperatures (5,6) The level of chloride and its manner of incorporation (Le., either within the crystal lattice or merely as an intimate mixture) may be critical parameters to the effectiveness of the compound as a superconductor. In the past, the methods for the determination of halogens in these types of materials have included such instrumental techniques as mass spectrometry (7), neutron activation radioactive tracer techniques (IO),and specanalysis (8,9), trophotometry (11, 12). These techniques yield excellent results but require either expensive instrumentation, extensive sample preparation, or both. Pelosi and co-workers (13)describe a coulometric procedure for chloride determination, but like the classical argentiometric titration on which it is based, the method does not distinguish well between chloride and bromide, and suffers serious interference from sulfide. Techniques involving ion-selective electrodes exhibit similar problems. Murphy et al. (14) discuss a separation procedure for the halogens but it is laborious. In this paper are described procedures for the rapid determination of not only chloride but of all the expected anionic components in cadmium sulfide samples exhibiting super-conducting-like behavior, using ion chromatography.
EXPERIMENTAL SECTION Apparatus and Reagents. The ion chromatograph used in all measurements was a Dionex Model 10, modified with a dual reciprocating-pistonpump to minimize pulsations and with 10-L eluent reservoirs. The chromatographic parameters are detailed in Table I. A commercially available computing integrator was
Table I. Ion Chromatographic Parameters eluent
0.003 mol/L NaHCO, and 0,0018 mol/L Na,CO, (pH 9.75) flow rate 2.0 mL/min separator column 3 X 150 rnm anion precolunm plus 3 X 500 mm standard anion column suppressor column 6 X 250 mm anion suppressor column injection volume 100 pL quantitation peak height chloride, 3.8 min; sulfate, 21.1 min elution time used for data acquisition and manipulation. The extractions of the soluble components in the samples were performed in a 2-L, 125-W ultrasonic bath. The chloride and sulfate standards were prepared from NBS Purified Reagents (15), hydrochloric acid and sulfuric acid, and standardized by controlled-current coulometric titration. With the exception of sample I, the cadmium sulfide samples, doped with chloride, were prepared by S. Block, H. Parker, and G. J. Piermarini at the National Bureau of Standards by either of two procedures: precipitation from solution or solid-state reaction at 400 "C. Sample I was prepared by Alfa Products, Danvers, MA, and was obtained through C. G. Homan of the US.Army Watervliet Arsenal, Watervliet, NY. All other chemicals used in this investigation were ACS reagent grade. Chloride and sulfate blanks were checked on these reagents and found not to be a factor at the level of concentration and precision reported herein. Total Chlorine and Sulfur. Samples of approximately 100 mg of the various preparations of chloride-dopedcadmium sulfide were dissolved in 20 mL of a 1:l mixture of a carbonate buffer solution (0.003 mol/L NaHC03 and 0.0018 mol/L NazC03)and 30% hydrogen peroxide. For the samples which had been prepared by precipitation from solution, heating at 80-90 "C for 30 min in an open flask on a hot plate was sufficient to effect dissolution. However, the samples prepared by solid-state reaction at 400 "C had become sintered and required refluxing in the
This article not subject to US. Copyright. Published I982 by the American Chemical Society
ANALYTICAL CHEMISTRY, VOL. 54, NO. 2, FEBRUARY 1982
Table 11. Recovery of Chloride after Hydrogen Peroxide Treatment sample 1 2 3 4a a
amt of chloride, p g added found 47 05 4614 4445 4501
467 2 4514 4373 4198
99.3 9951 98.4 93.3
C D
E F G
H I J
wt %
wt%
mass balance, wt %
J
3.86 0.83 1.41 1.64 0.86 1.14 1.60
20.1 21.9 21.3 21.4 21.6 21.0 20.9
100.5 100.8 99.6 100.6 99.5 97.6 98.3
K
L M N P
Table 111. Total Chlorine and Sulfur in Doped Cadmium Sulfide (Open Flask Dissolution)
A B
sample
0
Sample 4 was evaporated to dryness.
sample
Table IV. Total Chlorine and Sulfur in Doped Cadmium Sulfide (Reflux Dissolution) chlorine,
recovery, %
chlorine, wt %
sulfur, wt %
mass balance, wt %
3.21 0.83 4.11 0.68 0.71 0.69 3.76 2.80 1.04 3.92
20.2 21.9 19.3 22.2 21.9 22.0 19.7 20.8 21.6 19.9
99.3 100.8 97.6 101.8 100.5 100.9 98.5 100.9 100.0 99.8
RESULTS AND DISCUSSION Previous methods for the analysis of cadmium sulfide generally have used concentrated nitric acid to dissolve the sample (13,16,17). This was deemed unacceptable for this investigation for several reasons: incompatibility of the excess nitrate with ion chromatography (18);loss of sulfur as hydrogen sulfide; and potential oxidation of chloride to chlorine. Hydrogen peroxide is an ideal reagent for this application in that it is available in a high state of purity and adds no anions to the solution (other than hydroxide). In an alkaline solution, hydrogen peroxide quantitatively oxidizes sulfide to sulfate but does not oxidize chloride. To prove this last point, we subjected several solutions with known amounts of chloride added to the alkaline peroxide treatment. The results are shown in Table 11. Even in sample 4 which was inadvertently evaporated to dryness during the peroxide destruction stage, recovery was better than 93%. During the dissolution process, a white precipitate of cadmium carbonate forms. However, this precipitate is so finely divided and the solution so dilute that neither coprecipitation nor occlusion of sulfate or chloride seems to be a problem. Results corresponding to the open flask dissolution procedure are shown in Table I11 and to the reflux procedure in Table IV. Each value represents the mean of at least three
sulfur,
Table V. Soluble Chloride and Sulfate in Doped Cadmium Sulfide sample
chloride, wt %
A B C D
1.48 0.09 2.56 0.07 0.09 1.13 0.44 1.87 0.84 1.21 1.71
E H I J
N
0
alkaline peroxide solution for 8 h for total dissolution. After the samples in the open flasks were dissolved, additional carbonate buffer was added and then boiled to destroy the excess peroxide. The resulting solutions containing chloride and sulfate were diluted to 1 L and injected into the ion chromatograph through a syringe filter. Standards were prepared to approximate the levels of chloride and sulfate in the analyte solutions and were injected to recalibrate the instrument after every three samples. Quantitation was by comparison of peak heights. Soluble Chloride and Sulfate. To analyze the doped cadmium sulfide for leachable anions, 100-mgsamples were placed in Erlenmeyer flasks with 100 mL of the carbonate buffer solution and sonicated for 20 min in an ultrasonic bath. The supernatent liquid was injected into the ion chromatograph through a syringe filter. In the materials analyzed, only chloride and sulfate were evident upon examination of the chromatogram. Had other anionic species (such as fluoride, bromide, nitrate, or phosphate) been present as contaminants in the material, they could also have been determined. Calibration and quantitation were by the methods described in the previous section.
341
P
sulfate, wt % 0.79 0.92 0.34 0.54 0.55 0.04 0.16
