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Articles

Measurement of CO₂ Dissolved in Aqueous Solutions Using a Modified Infrared Gas Analyzer System ¹

Department of Crop and Soil Sciences, Michigan State University, East Lansing, Michigan 48824-1114

Total dissolved inorganic carbon (CO₂) and aqueous carbon dioxide (H₂CO₃^*) in nutrient solutions may be measured by the injection of small gas or liquid samples (1 microliter to 8 milliliters) into a gas stripping column connected in-line with an infrared gas analyzer. The measurement of CO₂ in solution requires sample acidification, while H₂CO₃^* and gaseous CO₂ are measured without the addition of lactic acid. The standard curve for CO₂ was linear up to 300 nanomoles CO₂. Maximum sensitivity was approximately 300 picomoles. Measurements of H₂CO₃^* were independent of pH. Consequently, CO₂ and H₂CO₃^* could be used to calculate the pH, HCO₃^–, and CO₃^2– values of nutrient solutions. Injection and complete analyses required from 0.8 to 2 minutes.