Determination of Chlorine in a Polyvinyl Chloride Matrix Using the Schoniger Oxygen Flask and Atomic Absorption Spectrometry Estelle D. Truscott B. F. Goodrich Chemical Company, Development Center, Avon Lake, Ohio 44012
ONLYA FEW CHLORIDE procedures employing atomic absorption spectrometry have been described in the literature (1-5). These publications were concerned with the determination of chloride by flame photometry in aqueous solutions. The procedure outlined in this paper describes the determination of the total chlorine content in a polyvinyl chloride matrix. The samples are first ashed in a Schoniger (6) oxygen flask, and then the chloride is determined by atomic absorption employing a technique similar to that which has been reported for determining sulfur in fuel oil (7). The present procedure involves reducing with hydrogen peroxide any chlorine released by combustion and absorbing the chloride into a sodium hydroxide solution. Dilute nitric acid is added to destroy the hydrogen peroxide and to neutralize the sodium hydroxide. A measured amount of silver ion in excess of the chloride present is added to the solution,
A Thomas-Ogg combustion apparatus with infrared light ignition was employed to initiate combustion of the sample. Reagents. A standard stock solution of silver was obtained from Hartman-Leddon Company, Philadelphia, Pa. Procedure. A 0.05-gram sample is combusted in the Schoniger Oxygen flask. The combustion products are absorbed by the method of Viebock (8) in a solution containing 50 ml of 0.1N NaOH, 0.5 ml of 30% H202, and 70 ml of distilled HzO. The absorption is facilitated by mixing on a high speed magnetic stirrer for 10 minutes until all the vapors have disappeared. The solution is quantitatively transferred to a 1-liter volumetric flask. Dilute HNO, (2:l) is added (2 ml) and mixed for 1 minute. Standardized 0.05N AgN03 (8.5 ml) is added, mixed, and diluted to 1 liter. To ensure complete precipitation, the solutions are stored overnight in the dark. A 10-ml aliquot of the slurry is centrifuged for 10 minutes at 2700 RPM and is then ready for analysis.
Table I. Chlorine in PVC Plastisols Containing K2CO3 Wt C1 in PVC matrix Schonigera AASa analysis Recoverybratio analysis Recoverybratio 27.35 1.004 27.47 1.008 23.26 1.007 22.33 0.967 20.42 0.980 19.71 0.946 19.93 0.995 19.19 0.958 17.33 0.980 16.44 0.929
z
X-ray corrected Theoretical for matrix 27.24 27.24 23.42 23.09 20.84 20.82 20.01 20.03 18.18 17.69 a Average of two analyses. Z C1, analyzed Recovery ratio = C1, theoretical’
Wt
Z KzC03
in PVC matrix 0
15.25 23.52 26.47 35.06
z
resulting in the precipitation of silver chloride. The excess silver is measured by atomic absorption. The difference between the total silver added and the silver analyzed in the supernatant liquid is the amount of silver precipitated as the chloride. The silver ion concentration difference is calculated as the per cent chlorine in the polymer by using the silver-tochloride weight relationship. EXPERIMENTAL Apparatus. A Perkin-Elmer Model 303 atomic absorption spectrophotometer equipped with a silver, hollow-cathode lamp was used to obtain the experimental data. The following instrumental parameters were used : range = UV, wavelength 328, slit = 4, source = 12 mA. The Schoniger flask was used as the combustion vessel.
(1) J. B. Ezell, Jr., At. Absorption Newslett., 6, 84 (1967). (2) U. Westerlund-Helmerson, ibid., 5 , 97 (1966). (3) H. Bartels, ibid., 6, 132 (1967). (4) 0. Menis, H. P. House, and T. C. Rains, ANAL.CHEM.,29, 76 (1957). ( 5 ) W. Reichel and L. Acs, ibid., 41, 1886 (1969). (6) W. Schoniger, Mikrochim. Acta, 1955, 123-9. (7) Harry W. Lautenbacker and H. Weldon Baker, Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Cleveland, Ohio, 1969.
Standard solutions containing the same reagents as the combusted samples are prepared. RESULTS AND DISCUSSION
The matrices prepared for these analyses included a PVC plastisol (100 parts PVC 100 parts dioctyl phthalate fused at 350 OF for 5 minutes) and a series of plastisols containing various levels of potassium carbonate. Attempts to analyze these samples by conventional Schoniger produced results which were low when compared to the theoretical. The AAS analysis was obtained with standards containing the same reagents as the combusted samples to compensate for any matrix effects. The analyzed results were within =t0.4z of the theoretical chlorine content of the polymer samples. X-ray fluorescent chlorine analysis (9) was also obtained for cross-checking the AAS analysis. Table I tabulates the data of the three methods for chlorine analysis of PVC/K2C03 plastisols.
+
RECEIVED for review April 13, 1970. Accepted August 31, 1970. (8) Franz Viebock, Chem. Listy, 16, 248 (1922). 40, 1080 (1968). (9) J. W. Criss and L. S. Birks, ANAL.CHEM.,
ANALYTICAL CHEMISTRY, VOL. 42, NO. 13, NOVEMBER 1970
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