Measurements of carbon dioxide with the air-gap electrode: Determination of the total inorganic and the total organic carbon contents in waters

Abstract

The newly developed air-gap electrode has been used in water analysis for a study of the carbon balance in waste waters and lake waters. The total inorganic carbon (TIC) content is determined directly; the total carbon (TC) and the total organic carbon (TOC) content are determined after wet chemical oxidation of the sample, directly or after acidification, by an aikalinc potassium persulphatc solution. The resulting total carbonate content can be determined directly if the concentration exceeds 2 m M. In order to cover the range down to 0.1 m M total carbonate, a preconcentration technique was developed, based on precipitation of very slightly soluble lead carbonate in alkaline solution. The analysis can be done quickly and reliably in this way. The relative standard deviation is less than 3% and the method is highly selective, as only carbonate is sensed after selective release as CO 2 The peculiarities of carbon dioxide measurements with gas-sensing electrodes are indicated. Optimal measuring parameters for the air-gap carbon dioxide sensor are suggested.