泥炭样品当中α-纤维素提取的实验方法探讨

Improved peat α-cellulose extraction procedure

目前,泥炭α-纤维素同位素研究已广泛应用于古气候、古环境重建,因而泥炭α-纤维素的提取也就显得尤为重要,但国内外泥炭α-纤维素的提取方法存在差异,并未形成比较统一的α-纤维素提取流程,在一定程度上限制了各实验室之间泥炭α-纤维素同位素数据的对比分析。在前人树轮、湖泊和泥炭α-纤维素提取流程的基础之上进行改善,经过反复的条件实验,最终建立了适合泥炭岩芯样品的α-纤维素提取方法。对泥炭α-纤维素提取流程的改进主要表现在4个方面:(1)样品处理前增加了清洗步骤,并设计了简单的清洗装置,可以有效清除粘土和矿物等杂质。(2)α-纤维素提取自始至终是在10 ml的Teflon离心管中进行,避免了在实验过程中多次转移样品而造成样品的损失,同时使用离心机分离缩短了样品的制备时间,并实现了α-纤维素的批量化提取。(3)NaClO2的漂白和不同浓度的NaOH溶液的碱洗取代有机溶剂的萃取。(4)α-纤维素提取流程中增加了样品的均一化处理,保证了测试样品具有较好的代表性。红外光谱分析结果证明提取的纤维素是比较纯的α-纤维素,对40个泥炭岩芯样品α-纤维素碳同位素的相对误差分析和线性回归分析,进一步强调在α-纤维素提取流程中样品均一化处理的必要性。

Isotopes of peat α-cellulose have been increasingly applied in paleoclimatic and paleoenvironmental reconstructions,therefore,the simplification and unification of the extraction procedure for peat α-cellulose is urgently needed. Until now,the discrepancy in peat α-cellulose extraction procedures largely limited the comparative studies of reported isotopic data of peat α-cellulose from different labs and research groups. Based on the classical peat α-cellulose extraction procedure,and referring to the relevant α-cellulose extraction procedures for tree rings,lacustrine sediments and so on,after a systematically and repeatedly conditional experiment,the paper finally established an effective peat α-cellulose extraction procedure. The improved peat α-cellulose extraction procedure are simply outlined as following：（1）original peat core samples were washed with deionized water in a specific and simple cleaning device,for the effective removal of clay and minerals;（2）the wet samples were dried in the oven（-70 ℃）,and then were finely powdered in an agate mortar with pestle;（3）humus in samples were removed by Na OH（5%）dissolution at room temperature for 24 h;（4）carbonate in samples were removed by HCl（5%）dissolution in a 80 ℃ water bath for 1 h;（5）lignin in samples were removed by sodium chlorite and acetic acid（acetic acid were firstly added）dissolution in a 80 ℃ water bath for 1 h;（6）remains of non-cellulose poly-saccharides（hemicellulose）were removed by Na OH（10%）dissolution in a 80 ℃ water bath for 1 h,and then by Na OH（17%）dissolution at room temperature for 45 min;（7）the samples were neutralized with HCl（1%）,and then washed with a large amount of deionized water;（8）the extracts were homogenized by supersonically treated for 10 min;（9）the extracted α-cellulose samples were dried in a -70 ℃ oven. The purity degree was examined by comparative infrared spectrum analysis of α-cellulose extracted from peat and modern plant leaf with international standard tree ring α-cellulose. Finally,carbon isotopic composition of α-cellulose extracted from 40 peat-core samples were double or triple measured. The analyses on the obtained carbon isotopic data demonstrated that the established peat α-cellulose extraction procedure is effective and efficient. The improvements of the peat α-cellulose extraction procedure are mainly focus on the following 4 aspects：（1）a simple cleaning device was designed for the effective removal of impurities,such as clay and minerals;（2）the whole extraction procedure was performed in the same 10 ml Teflon centrifuge tube to avoid the loss of samples,and a centrifuge machine was used for the reduction of the extraction time;（3）the organic solvent extraction was replaced by bleaching by sodium chlorite solution and alkaline cleaning by sodium hydroxide solution with different concentrations;（4）final homogenization of the extracted α-cellulose for better representativeness. Briefly,a better peat α-cellulose extraction procedure has been established,due to its minor sample loess,easy and quick handling,stable and precise isotopic data.