A comparison of methods for the preparation of 14C-labelled plant tissues for liquid scintillation counting

Abstract

Four methods for the preparation of 14C-labelled plant tissues for liquid scintillation counting have been compared for accuracy and precision. The wet oxidation method of Mahin and Lofberg, although easy and rapid, proved to be unsuitable for obtaining a reliable estimate of 14C present in lyophilized plant material, showing non-quantitative recovery and poor reproducibility. Solubilization in Hyamine hydroxide provided accurate and reproducible results, if experimental conditions were strictly adhered to; however, especially when larger samples were employed, severe—and variable—color quenching resulted in very low counting efficiency, which necessitated construction of quench correction curves specific for each source of plant material. Van Slyke wet combustion, in a device slightly modified after Jeffay and Alvarez, on the other hand, always resulted in reproducible and reliable data, irrespective of the carbon compound administered and the nature of the plant material. With samples of up to about 10 mg, Schöniger dry combustion in the Micro-Mat BF 5010 oxidation system even outrivalled Van Slyke wet combustion, because of speed and ease of manipulation. The latter methods are, therefore, evidently superior to the wet oxidation method of Mahin and Lofberg and solubilization in Hyamine hydroxide in preparing plant tissue samples for liquid scintillation counting.