Effects of chemical pretreatments on δ18O measurements, chemical composition, and morphology of chironomid head capsules
Effects of chemical pretreatments on δ18O measurements, chemical composition, and morphology of chironomid head capsules
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化学预处理对摇蚊头胶囊 δ18O 测量、化学成分和形态的影响
DOI：
10.1007/s10933-009-9374-z
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发表时间：
2010
影响因子：
2.1
通讯作者：
A. Lotter
中科院分区：
文献类型：
--
作者：
F. Verbruggen;O. Heiri;G. Reichart;J. D. Leeuw;K. Nierop;A. Lotter
对湖泊沉积物中摇蚊头壳化石的稳定氧同位素测量表明，这些几丁质遗骸可以用来重建过去的湖水δ 18 O，并间接重建过去的气候变化。我们研究了化学预处理程序的化学和稳定的氧同位素组成的影响，和形态的摇蚊幼虫。使用碱、酸和碳酸钠通过选择性去除几丁质或蛋白质来改变摇蚊幼虫的化学组成和形态结构。热解产物的气相色谱图显示，氯酸钠导致脱蛋白，而盐酸和HF的组合使用的结果在部分甲壳素去除。用KOH预处理的头囊含有几丁质衍生部分和蛋白质衍生部分，尽管蛋白质的浓度降低，尤其是在高浓度（28%）和温度（100°C）下的KOH处理后。扫描电子显微镜证实，蛋白质基质仍然存在于现代和化石的头囊KOH处理后。然而，这种基质在用NaClO2预处理的头囊中基本上不存在。甲壳素和蛋白质在我们的样品中的比例的变化与摇蚊δ 18 O值的差异。我们的研究结果表明，脱蛋白导致摇蚊的δ 18 O相对增加，而甲壳素的去除导致δ 18 O值下降。因此，我们不建议在分析摇蚊体δ 18 O之前使用酸或长时间（≥1 h）暴露于热碱（70°C）。甲壳素的提纯过程中，甲壳素的质量损失很大，这可能会影响到对摇蚊体δ 18 O的测量。在对摇蚊δ 18 O分析的样品进行预处理时，需要谨慎和标准化，以确保可靠、可比和可重现的结果。
Stable oxygen isotope measurements on fossil chironomid head capsules from lake sediments show that these chitinous remains can be used to reconstruct past lake water δ18O and, indirectly, past climate change. We examined the impact of chemical pretreatment procedures on the chemical and stable oxygen isotope composition, and morphology of chironomid cuticles. Use of alkali, acids, and sodium chlorite alters the chemical composition and the morphological structure of chironomid cuticles by selective removal of chitin or proteins. Gas chromatograms of pyrolyzates show that NaClO2 causes deproteination, whereas the combined use of HCl and HF results in partial chitin removal. Head capsules pretreated with KOH contained both chitin- and protein-derived moieties, although the concentration of protein was reduced, especially after KOH treatment at high concentration (28%) and temperature (100°C). Scanning electron microscopy confirmed that a proteinaceous matrix is still present in modern and fossil head capsules after KOH treatment. This matrix, however, is largely absent in head capsules pretreated with NaClO2. A change in the proportion of chitin and proteins in our samples was associated with differences in chironomid δ18O values. Our results suggest that deproteination results in a relative increase of chironomid δ18O, whereas removal of chitin leads to decreased δ18O values. We therefore discourage the use of acids or prolonged (≥1 h) exposure to hot alkali (70°C) prior to chironomid δ18O analysis. Chitin purification by sodium chlorite causes significant weight loss, which may preclude down-core chironomid δ18O measurements. Caution and standardization are required when pretreating samples for chironomid δ18O analysis to ensure reliable, comparable, and reproducible results.