MS2000激光粒度仪测量第四纪沉积物粒度的定量进样研究

粒度是第四纪古气候与古环境重建的常用替代指标,目前通常采用Mastersizer2000激光粒度仪进行分析,该测试仪器优点是速度快、精度高、重复性好,缺点是进样过程未实现定量化,对部分沉积样品的分析结果出现一定的随机性和不确定性,分析结果易产生人为误差。为探究样品量和进样方法对测试结果可能造成的影响,本研究选取6类代表性第四纪松散沉积物,预处理后分别采用倾倒法、吸管法及定量进样法进行多次重复实验。结果显示:粒度组分越单一,不同进样方法造成的结果误差越小;如果沉积物含有多个粒度组分,而预处理样品量过多,倾倒法容易造成粒度结果偏细,吸管法往往造成实验结果偏粗,定量进样法实验结果居于前两者之间。采用烧失量法计算沉积物中碳酸盐、有机质含量,结合马尔文激光粒度仪测试原理及多次定量重复实验结果,计算了一次实验所需样品量,发现其与中值粒径和碳酸盐、有机质(合称杂质)含量呈线性正相关。根据该线性关系式,在分析第四纪沉积物中值粒径范围及杂质含量的前提下,可计算一次测试所需样品量,将全部预处理后样品倒入测试烧杯中,可有效避免样品量和进样方法对样品粒度实验结果造成的误差。

Quantitative sampling for grain size analysis by MS2000 laser analyzer

Grain size is a proxy commonly used for Quaternary paleoclimate and paleoenvironment reconstruction.The Mastersizer 2000 laser analyzer is widely adopted to measure the grain size.The facility is advantaged by fast speed,high precision and good repeatability.However,the sampling introduction of it is not quantified and there may occur great randomness and uncertainty prone to human errors.In order to study the possible influences of sample amount and sample introduction methods on the test results,six types of representative Quaternary sediments were selected for repeated experiments,respectively with methods of dumping,pipette and quota sample introduction after pretreatment.The results show that the more uniform the grain size component,the smaller the difference in various sample introduction methods.If the sediment contained multiple types of grain size components and the pretreated sample amount was much enough,the grain size result of the dumping method was prone to be finer,while that of the pipette method was often coarser,and the quota sample introduction method resulted in between.Loss-of-ignition was used to calculate the content of carbonate and organic matter in the sediments.Upon the principle of the Mastersizer 2000 laser grain size analyzer and the results of repeated quantification experiments,we calculate the sample amount needed for one test.It is found that the needed amount has positive linear correlation with median grain size and impurity content.Afterwards the linear relation was calculated.Based on the universal linear relation,the median diameter range and the content of carbonate and organic matter and other impurities in the Quaternary sediments, the sample amount needed for one test could be calculated. Pouring all the pretreated samples into the test beaker couldeffectively avoid the unknown impacts on experimental results caused by sample amount and sample introduction methods.