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*Department of Anesthesiology and General Intensive Care (B), University of Vienna;
Institute of Applied Synthetic Chemistry, Technical University of Vienna; and
L. Boltzmann Institute for Anesthesiology and Intensive Care, Vienna, Austria
Address correspondence and reprint requests to Erich Knolle, MD, Department of Anesthesiology and General Intensive Care (B), University of Vienna, Waehringer Guertel 18–20, A-1090 Vienna, Austria. Address e-mail to erich.knolle{at}univie.ac.at
Alkali hydroxide-free absorbents change color markedly when they dry, whereas absorbents containing alkali hydroxides do not. We investigated whether this observation can be explained by the weaker hygroscopic properties of pure calcium hydroxide compared with alkali hydroxides. Samples of the alkali hydroxide-free absorbents Amsorb® or Superia® and samples of these two absorbents with 1% or 3% NaOH or 3% KOH added were dried in a moisture analyzer at 105°C to determine their moisture content and to assess the color of the samples during drying (each group, n = 5). Additionally, we repeated the experiments with pulverized samples of Baralyme® and Spherasorb®, which contain approximately 4% KOH and 1% NaOH, respectively. Amsorb® and Superia® changed color long before they were dry. After the addition of 1% NaOH, and as with the Spherasorb® samples, the drying time required for a color change was longer, and the intensity of the resulting violet was less. This effect was even stronger when 3% NaOH was added. The samples with added KOH and the Baralyme® did not change color at all on drying. We conclude that the differences in color change on drying in absorbents with varying NaOH or KOH content cannot be explained by larger water retention because of the hygroscopic properties of the alkali hydroxides.
IMPLICATIONS: In an in vitro study, the moisture content and color change on drying were determined in samples of Amsorb® or Superia® and in the same absorbents with added NaOH or KOH. With increasing concentrations of alkali hydroxide, a delay in the color change upon drying was observed. However, the moisture content did not change.
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  C. D. Barth, M. B. Dunning III, L. Bretscher, and H. J. Woehlck Barium Hydroxide Lime Turns Yellow After Desiccation Anesth. Analg., September 1, 2005; 101(3): 748 - 752. [Abstract] [Full Text] [PDF]
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