摘要
扩散法与质谱测定技术相结合,被广泛应用于环境、生态和农业领域中土壤、水等样品中无机氮15N同位素丰度的测定。为建立一套可快速、准确测定土壤无机氮15N同位素丰度的扩散培养体系,针对土壤样品无机氮量的变化特点,从培养温度、培养时间、试剂选择和用量等方面对扩散条件进行优化。结果发现,对于大部分无机氮浓度大于2 mg L^(-1)的土壤样品,20 ml土壤提取液,在不小于250 ml的蓝盖瓶中,悬挂两张各滴加了10μl 1 mol L^(-1)草酸的滤纸,加入0.1 g的Mg O,25℃下以140 r min-1的转速振荡培养24 h即可完成对样品中NH4+-N的扩散与回收;换入2张加酸滤纸继续摇培48 h可基本去除残余的NH4+-N;再换入2张加酸滤纸并加入0.1 g的戴氏合金振荡培养24 h即可。对于无机氮浓度低于2 mg L^(-1)的土壤提取液,需用50 ml提取液按以上条件进行扩散培养即可保证测定结果的准确性。本方法大大缩短了扩散法所需的实验周期,实现在一份样品内同时完成NH4+-N和NO3--N的扩散与回收,减少了样品的需要量,并通过优化Mg O、戴氏合金(Devarda’s alloy)的用量减少杂质氮可能带来的污染。
[ Objective ] The use of the diffusion method coupled with mass spectrometry to determine δ^15N of inorganic nitrogen in soil and water samples in researches in the environmental, ecological and agricultural fields. Compared with the distillation method, the diffusion method consumes less labor and material resources, and can be used in massive operation. The diffusion method not only works when the sample is low in nitrogen content, but also avoids the risk of cross contamination and the need for fractionation. However, for application of the diffusion method, it is essential for the researchers in China to have a sound diffusion-incubation system which is able to perform rapid and accurate determination of δ^15N of inorganic N in the soil. [Methods] The diffusion method proceeds as follows： put a set amount of soil extract in a small airtight grass container; add some alkaline reagent to convert NH4^＋-N into NH3, which is adsorbed by acid-spiked filter paper; for determination of NO3^--N, titrate some alkaline reagent to remove NH4^-N in the sample; and add some Devarda＇ s alloy to reduce NO3^--N into NH4^＋-N. In the light of characteristics of the variation of inorganic nitrogen in soil extracts, diffusion conditions, such as incubation temperature, incubation time, type and rate of reagents were tested and optimized. [Results] Results show that for soil extracts, 〉 2 mg L^-1 in inorganic N concentration, only 20 ml soil extract is needed, put it into a 250 ml flask; hang 2 pieces of filter paper spiked with 10 -tl 1 mol L-1 H2C204 each in the flask; add 0.1 g MgO, and then incubate the sample for 24 h at 25℃ on a rotator running at 140 r min^-1 to complete the processes of diffusion and recovery of NH4^＋-N; and then replace the used filter paper with two new ones also spiked with H2C2O4; incubate it on a rotator running at 140 r min^-1 for 48 h to remove remaining NH4^＋-N; and again replace the used filter paper with two new acid-spiked ones, add 0.1 g Devarda＇ s alloy, and incubate it for 24 h to complete the processes of diffusion and recovery of NO3^--N. For soil extracts 〈 2 mg L-1 in inorganic nitrogen concentration, 50 ml is needed to ensure accuracy of the determination once the same incubation procedure is followed. The experiment also reveals that nitrogen impurities that may affect accuracy of the determination, come mainly from highly purified water, filter paper, acid absorbent, MgO and Devarda＇ s alloy. To avoid the effects of the nitrogen impurities, samples should be incubated at 25℃ for 24 h, and filter paper dried as far as possible in NH3-free environment. In addition, results of the determination should be calibrated against that of the control. [ Conclusions ] It can be concluded that this method greatly shortens the incubation cycle of the general incubation method and is capable of accomplishing diffusion and recovery of both NH--N and NO--N simultaneously, decreasing the amount required of a sample and reducing the risk of contamination by nitrogen impurities by optimizing the rate of MgO and Devarda＇ s alloy. However, the diffusion method discussed here is oriented towards determination of ^15N-labeled soil extracts, 2 - 8 mg L^-1 in inorganic N concentration, but not applicable to determination of soils samples natural in ^15N abundance or low in nitrogen concentration. Consequently, in future studies, efforts should be devoted to such issues as how to remove nitrogen impurities and quickly, how to rule out the interference of soluble organic nitrogen in the soil.
出处
《土壤学报》
CAS
CSCD
北大核心
2017年第4期948-957,共10页
Acta Pedologica Sinica
基金
国家自然科学基金项目(41501254)
江苏高校优势学科建设工程资助项目资助~~
