Freeze-drying pretreatment improves organic carbon determinations of marine sediments
海洋沉积物有机碳分析方法中干燥预处理过程人为误差的发现及其意义

Using one fresh hemipelagic and two fresh coastal marine sediment samples collected on the continental slope of the South China Sea and in Jiaozhou Bay near Qingdao, China, we compared sample pretreatment schemes of organic carbon determination. By replacing the heat-drying step in the sample pretreatment scheme with a freeze-drying-under-vacuum step, the organic carbon content values of all three samples were more than 20% higher. GC-MS examination of the vapor phases collected during the heat-drying step confirmed the presence of organic carbon in these phases and revealed the composition of this organic carbon. When each sample was subjected to freeze-drying for different times, identical results were obtained and no organic carbon loss was observed. Based on these observations, we believe that there is a large systematic error (>20%) caused by the heat-drying step in the common sample pretreatment scheme and that this error could be effectively corrected if a freeze-drying-under-vacuum step is used instead. Considering the significance of this error, we believe that some previously published organic carbon data, as well as the scientific understandings that were based on those data, may need to be re-evaluated.