Published: Jan 1966
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Acetate grinding aids were analyzed quantitatively using a gas chromatograph equipped with a hydrogen flame detector. The acetate first had to be concentrated and converted to acetic acid. With mechanical stirring, 100 g of cement was added to 400 ml of phosphoric acid. The portion of the mixture which distilled at 115 C within 1 hr was collected. The pH of the distillate was adjusted to 11, and the distillate concentrated to 5 ml. The pH of the concentrate was adjusted to 1 with hydrochloric acid and the volume brought up to 10 ml with water. A 0.001 ml sample of this solution was injected into the chromatograph. The column was packed with Fluoropak support coated with 8 per cent Carbowax and 2 per cent terephthalic acid, and was operated at 175 C. Helium at a flow rate of 70 ml/min was the carrier gas. The column first had to be primed with large doses of water containing 0.1 per cent acetic acid. Acetate content was determined by a comparison of the peak height of the known amounts of acetic acid. With 10 samples, the coefficient of variation was 5.0 per cent for interground cement. It was 14.7 per cent for 9 millground samples. Sensitivity was about 25 ppm for unconcentrated acetate. Concentration increased the sensitivity about 20 times. With special techniques the limit of detection can be lowered to 25 ppb.
chemical analysis, cement, acetate, gas chromatography, acetic acid, quantitative analysis
Wexle, A. S.
Manager of the Analytical Laboratory, W. R. Grace & Co., Cambridge, Mass.