Kroukamp E M, Godeto T W, Forbes P B C
Department of Chemistry, Faculty of Natural and Agricultural Sciences, University of Pretoria, Lynnwood Road, Pretoria, 0002, South Africa.
Spectrum Central Analytical Facility, Faculty of Science, University of Johannesburg, Kingsway Road, Johannesburg, 2006, South Africa.
Environ Monit Assess. 2017 Aug 13;189(9):451. doi: 10.1007/s10661-017-6155-4.
The effects of different sample preparation strategies and storage on metal(loid) fractionation trends in plant material is largely underresearched. In this study, a bulk sample of lichen Parmotrema austrosinense (Zahlbr.) Hale was analysed for its total extractable metal(loid) content by ICP-MS, and was determined to be adequately homogenous (<5% RSD) for most elements. Several subsets of this sample were prepared utilising a range of sample preservation techniques and subjected to a modified sequential extraction procedure or to total metal extraction. Both experiments were repeated after 1-month storage at 4 °C. Cryogenic freezing gave the best reproducibility for total extractable elemental concentrations between months, indicating this to be the most suitable method of sample preparation in such studies. The combined extraction efficiencies were >82% for As, Cu, Mn, Pb, Sr and Zn but poor for other elements, where sample preparation strategies 'no sample preparation' and 'dried in a desiccator' had the best extraction recoveries. Cryogenic freezing procedures had a significantly (p < 0.05) negative effect on metal extractability, and is therefore inappropriate for sequential extraction procedures in lichens. Biotransformation over a period of a month is suspected for most elements, with the exception of Sr and Zn, where changes in the fractionation patterns were statistically significant (p < 0.05), indicating the need for minimal delay in sample cleaning and preservation when species fractionation patterns are of interest. This study also shows that the assumption that species stability can be ensured through cryopreservation and freeze drying techniques needs to be revisited.
不同样品制备策略和储存对植物材料中金属（类金属）分级趋势的影响在很大程度上尚未得到充分研究。在本研究中，通过电感耦合等离子体质谱法（ICP-MS）分析了地衣南方 Parmotrema austrosinense（Zahlbr.）Hale 的大量样品中的总可提取金属（类金属）含量，并确定其对于大多数元素而言具有足够的均匀性（相对标准偏差<5%）。利用一系列样品保存技术制备了该样品的几个子集，并对其进行了改进的连续提取程序或总金属提取。在 4°C 下储存 1 个月后重复了这两个实验。低温冷冻在不同月份之间对于总可提取元素浓度给出了最佳的重现性，表明这是此类研究中最适合的样品制备方法。砷、铜、锰、铅、锶和锌的联合提取效率>82%，但其他元素的提取效率较差，其中“不进行样品制备”和“在干燥器中干燥”的样品制备策略具有最佳的提取回收率。低温冷冻程序对金属的可提取性有显著（p<0.05）负面影响，因此不适用于地衣的连续提取程序。除了锶和锌之外，大多数元素在一个月的时间内都疑似发生了生物转化，其中分级模式的变化具有统计学意义（p<0.05），这表明当关注物种分级模式时，在样品清理和保存方面需要尽量减少延迟。本研究还表明，通过冷冻保存和冷冻干燥技术可以确保物种稳定性的假设需要重新审视。
