Submitted to: Frontiers in Environmental Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/2017
Publication Date: 11/28/2017
Citation: Loughrin, J.H., Antle, S.W., Polk, J. 2017. A gas chromatographic method for the determination of bicarbonate and dissolved gases. Frontiers in Environmental Science. 5:65. https://doi.org/10.3389/fenvs.2017.00065.
Interpretive Summary: Determining the concentration of carbon dioxide in water is important due to its importance in many biological processes including wastewater treatment. Carbon dioxide dissolved in water exists in different forms such as solvated carbon dioxide, carbonic acid, and bicarbonate. The determination of dissolved carbon dioxide is usually done by neutralization of its alkaline form, bicarbonate, with an acid. A more rapid method for the rapid determination of the concentrations of dissolved carbon dioxide in water and its assortment into its solvated and bicarbonate forms is presented. Small water samples were collected in the field and injected into vials partially filled with dilute hydrochloric acid. A portion of the gas sample in the vials was injected onto a gas chromatograph instrument to measure the carbon dioxide and using the measured pH of the sample and well-known equations, the concentrations of carbon dioxide and its various forms could be measured. Natural water samples as well as wastewater from a sewage treatment plant and a swine rearing operation were analyzed by this method and the results compared favorably to those obtained by titration. The method can also be used to measure other dissolved gases such as methane and nitrous oxide.
Technical Abstract: A gas chromatographic method for the rapid determination of aqueous carbon dioxide and its speciation into solvated carbon dioxide and bicarbonate is presented. One-half mL samples are injected through a rubber septum into 20-mL vials that are filled with 9.5 mL of 0.1 N HCl. A one mL portion of the headspace is withdrawn and injected onto a gas chromatograph equipped with a thermal conductivity detector. Using the dimensionless Henry’s constant for carbon dioxide and an adaptation of the Henderson-Hasselbalch equation, carbon dioxide in the samples can be categorized among solvated, bicarbonate, and carbonate forms. Natural water samples as well as wastewater from a municipal sewage treatment plant and a swine rearing operation were analyzed by this method and the results compared favorably to those obtained by titration. Samples stored for up to five weeks showed no significant changes in carbon dioxide concentrations. In addition, using flame ionization and electron capture detectors, methane and nitrous oxide concentrations in the samples were also measured.