Coulometric Determination of Inorganic Halide Impurities in Polystyrene after Dissolution in 2-Butanone William R. Carroll’ Testing Laboratory, Bendix Corporation, Kansas City, Mo.
THE USUAL METHOD for the determination of halide ion impurities in polystyrene is to react a small sample (0.4 gram or less) with oxygen in a bomb or microcombustion furnace, collect the residue in appropriate solution, and analyze for halide amperometrically, coulometrically, etc. (1). The sample size permissable and the time required for each combustion limit the detection and number of replicates, thereby reducing reliability of data. The following procedure provides for the dissolution of polystyrene in 2-butanone (2) and the subsequent coulometric titration in 60% ethanol. The amounts determined as chloride were in the 5- to 20-pg range. EXPERIMENTAL
Apparatus. A Cotlove Chloridometer (Buchler Instruments, Fort Lee, N.J.) was used for coulometric measurements. Reagents. 2-Butanone (Eastman Chemical) was used without purification ; other chemicals were reagent grade. Procedure. Dissolve 2 to 3 grams of polystyrene (beads or foam) in 20 ml of 2-butanone. Precipitate the polystyrene by pouring the solution into an equal volume of 95% ethanol. Stir the ethanol mixture to coagulate the precipitate, decant the solution into a beaker, wash the precipitate with 5 ml of ethanol, and add the wash solution to the decantate (solution is turbid). Prepare several 50-ml blanks of 1 :1 butanoneethanol. Add a few glass beads to blank and samples and evaporate to 5 ml. 1 Present address, Chemistry Department, University of Missouri, Rolla, Mo. 65401.
Table I. Chloride Content of Polystyrene Beads as Determined by Coulometry, Mass Spectrometry, and Neutron Activation Coulometry 6.5 pprn; standard deviation = 1.6 (8 replicates) Mass 3, 89 ppm (duplicates) spectrometry Neutron 1, 0.8 ppm (duplicates) activation
Coulometric Measurements. Add 1 ml of 1.00 x lOPM standard sodium chloride, 1 ml of 0.6% gelatin solution, 6 ml of water, and 2 ml of 1M nitric acid to each of several 30-ml titration beakers. Decant the blanks and sample solutions into these beakers, wash the evaporation beakers with several small portions of ethanol, and bring the solution in each titration beaker to 25 ml with ethanol. Titrate blanks and samples alternately. RESULTS AND DISCUSSION
The addition of standard chloride ion was required by the low halide contents of the samples. The difference between blank and sample time to reach an end point was attributed to the halide content of the polystyrene. The rate of silver ion generation of the instrument was determined to be 0.56 pg/sec with standard deviation of 0.02 pg/sec for 23 measurements. Five to 20 pg of chloride were determined in 50 samples of polystyrene. Data (Table I) for one lot of 8 replicates are compared with values available from mass spectrometry (Bell & Howell, Pasadena, Calif.) and neutron activation, (Gulf General Atomic, San Diego, Calif.). No bromide or iodide was detected by either mass spectrometry or neutron activation.
(1) D. M. Coulson and L. A. Cavanaugh, ANAL.CHEM., 32, 1245
(1960). (2) J. Brandrup and E. H. Immergut, “Polymer Handbook,” Interscience, New York, N. Y.,1966, Chapter IV.
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RECEIVED for review August 13, 1969. Accepted September 22, 1969.
ANALYTICAL CHEMISTRY, VOL. 42, NO. 1, JANUARY 1970
