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Evaluation of sample pre-treatment and potential contamination of soluble carbon in soil extracts during lyophilisation

Coppens, Filip, Alavoine, Gonzague, Delfosse, Olivier, Recous, Sylvie
Soil biology & biochemistry 2009 v.41 no.6 pp. 1335-1337
soil analysis, solubility, soil organic carbon, pretreatment, freeze drying, carbon, accuracy, storage temperature, sampling
Lyophilisation of K2SO4 soil extracts has been proposed as a sample preparation technique before elemental analysis of carbon or nitrogen. However, previous measurements, based on wet oxidation or catalytic combustion, indicated that C measurements in lyophilised samples not always proved to be accurate. To determine whether the C analysis was affected by the lyophilisation process, an exploratory study was conducted to investigate the potential effects of the sample pre-treatment and of the lyophilisation process itself. This paper puts forward that the use of soil extracts, previously stored at -20 °C, may affect the recovery of salt in the samples and that contamination of the soluble carbon with exogenous C during lyophilisation is feasible. Therefore we recommend to use freshly prepared soil extracts for lyophilisation and always to include an internal standard among the unknown samples to account for a possible contamination.