样品采集和保存方法对水中溶解无机碳同位素分馏的影响

The influence of different pretreatment methods on the δ^(13)C value of dissolved inorganic carbon in water

为探明不同的样品前处理方法对水中溶解无机碳同位素的影响,寻找最佳的样品前处理方法,本文系统研究了不同样品采集方法(顶空样品瓶和聚乙烯瓶)和保存方法(不同的温度和是否加饱和氯化汞)以及储存时间对不同类型水样溶解无机碳同位素值的影响。结果表明:在水样类型相同的情况下,顶空瓶法较聚乙烯瓶法采集的水样δ^(13)C_(DIC)值更稳定;用聚乙烯瓶采集水样,加入饱和氯化汞能抑制微生物生长,不加饱和氯化汞的水样δ^(13)C_(DIC)值变化无规律且幅度大,而加了饱和氯化汞的水样δ^(13)C_(DIC)值更接近初始值,但随保存温度的升高和保存时间的推移,其δ^(13)C_(DIC)值逐渐偏重,主要受温度升高有利于HCO_3^-水解并释放CO_2的影响;不同类型水样在不加饱和氯化汞条件下,随保存时间加长,岩溶水的δ^(13)C_(DIC)值较初始值偏重,混合水和非岩溶区水δ^(13)C_(DIC)值较初始值偏轻。实验表明,用顶空样品瓶采集的水样保存100天,δ^(13)C_(DIC)最大变化值为0.42‰;用顶空样品瓶采集的水样保存时间长,δ^(13)C_(DIC)值变化小,最能反映样品的初始值,是最佳的样品前处理方法。用聚乙烯瓶采集的水样加饱和氯化汞并保存在5℃能满足样品短时间的保存。

In order to research the influence of different sample preparation methods on the dissolved inor- ganic carbon isotope in water samples, and to establish the best sample preparation method, this paper systematically study the sample collection （headspace vial and polyethylene bottle） methods, storage temperature, saturation mercuric chloride and storage duration which affect the dissolved inorganic carbon isotope value in different types of water samples. The results show that δ13CDIC headspace vial collection method is more stable than the polyethylene bottle collection method for the same water type. Using polyethylene bottle collection method and adding saturated mercury chloride may inhibit the growth of microorganisms. Theδ13CDIC value irregularly varies in a big range in case of no saturated mercury chloride added. In contrast, the δ13CDIC value roughly stabilizes at its initial value. The value increased in the case of the relative high temperature or long duration, which is mainly attributed to the release of CO2 in this condition of sample preserva- tion. Different types of water samples without saturated mercuric chloride and with prolonged preservation, the karst water δ13CDIC was more positive than the original value, and the mixed water and non- karst water was negative than the original value. The experiment results show, the maximum difference of δ13C value was merely 0.42‰ after 100 days of storage by using headspace vial sample collection, which is proved to be the best way of sample collection and preservation. In the meantime, the water sampled by polyethylene bot-tle collection method and stored in a 5℃ condition can last a short time to maintain the reliable δ13CDIC value.