鹤庆钻孔沉积物总有机碳、氮含量测定的前处理方法及其环境意义

湖泊沉积物中的总有机碳含量(TOC)、总有机氮含量(TN)和碳氮比值(C/N)已被广泛应用于第四纪湖泊古环境研究中。对湖泊沉积物样品进行TOC和TN测定前, 首先要有效去除沉积物中的无机碳酸盐, 同时较好地保留有机质组分, 才能使实验结果较准确地反映古气候环境的变化。选取鹤庆钻孔不同深度的不同岩性样品, 分别进行粒度、盐酸浓度、洗除残留酸方法等对去除碳酸盐和总有机碳测定结果影响的前处理条件实验, 根据测得的TOC、TN和C/N, 结合总无机碳酸盐含量(TIC), 确定了鹤庆钻孔沉积物有机碳含量测定的前处理方法:室温条件下, 将磨得足够细(无需过筛处理)的样品与足量浓度为2mol/L盐酸充分反应24小时, 期间超声震荡3次, 采用离心加速沉淀的方法清洗酸处理样品至中性, 烘干, 研磨均匀上机测定。结果显示, 该流程可有效去除沉积物中的无机碳酸盐, 测得的TOC、TN数值具有很好的稳定性和可重复性。在此基础上测定了鹤庆钻孔沉积物样品的TOC、C/N和TIC, 它们间存在很好的正相关关系, 指示了西南季风强度的变化。 

PRETREATMENT METHODS FOR ANALYZING THE TOTAL ORGANIC CARBON AND NITROGEN CONTENTS OF HEQING CORE SEDIMENTS AND THEIR ENVIRONMENTAL SIGNIFICANCES

Total organic carbon content (TOC),Total organic nitrogen content (TN) and their ration (C/N) of lacustrine sediments have been widely used in the Quaternary palaeoenvironment researches.Before measuring the TOC and TN of the sediments,the first important step is to effectively remove the inorganic carbonate,and preserve organic carbon well at the same time, which is the guarantee to good experiment results and accurate palaeoenvironment reconstruction.In order to apply a proper experimental procedure to the Heqing core sediments in Yunnan province, different lithological sediment samples from different depths are used to examine the influence of pretreatment methods,including grain size,the concentration of hydrochloric acid (HCl),and the method of washing the residual acid,on the analysis of total organic carbon content.According to the results of TOC,TN,C/N,and the total inorganic carbonate content (TIC),the pretreatment procedure of Heqing core sediments prior to TOC analysis is established as the followings: under normal condition,a sediment sample is grinded to be uniform and fine (no sieving process),which reacts with enough HCl whose concentration is 2mol/L for 24 hours; then centrifugal acceleration method is employed to cleaning the treated sample by acid to be neutral.This procedure can effectively remove the inorganic carbonate from the sediments,and the results of TOC and TN show good stability and reproducibility.The obtained sequences of TOC,TN,and C/N show good correlation,which all imply the intensity changes of the southwest monsoon.