Liquid scintillation counting can underestimate 14C-activity of 14CO2 trapped in NaOH

• Published in: Soil biology & biochemistry Vol. 166; p. 108576
• Main Authors: Boos, Elinor F., Magid, Jakob, Bruun, Sander, Jørgensen, Niels O.G.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.03.2022
• Subjects: 14C-activity loss; 14CO2; 14CO32; Base trap; Liquid scintillation counting; Scintillation cocktail; 14CO2; Liquid scintillation counting; Base trap; Scintillation cocktail; 14CO32; 14C-activity loss
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2022.108576

Mineralization of organic matter in environmental samples is frequently quantified by trapping 14CO2 released from the degradation of 14C-labelled compounds. However, when 14CO2 trapped in NaOH is quantified by liquid scintillation counting, 14C-activity can be gradually lost from the scintillation vials. When combining different molarities and volumes of NaOH and five commercial scintillation cocktails, we observed in some mixtures a rapid loss in 14C-activity of up to 10% after 0.5 h and 60% after 96 h, while other mixtures showed no loss of 14C-activity for at least 96 h. The 14C-activity loss depended on molarity, volume, and CO2 saturation of NaOH, as well as the scintillation cocktail used and the mixing ratio of the two components. We show that the decline of 14C-activity may be caused by the loss of 14CO2 from the scintillation vials. The loss of 14C-activity must be prevented and therefore we provide recommendations how to accurately quantify 14C-activity of 14CO2 trapped in NaOH using liquid scintillation counting. •14CO2 trapped in NaOH can be released when mixed with scintillation cocktail.•14C-activity lost can be as much as 10% after 0.5 h and 60% after 96 h.•14C-activity loss varies for different scintillation cocktails.•Greater molarity and volume, lower CO2-saturation of NaOH stabilize trapped 14CO2.