连续流同位素质谱测定水中溶解无机碳含量和碳同位素组成的方法研究

用连续流同位素质谱对水样中溶解无机碳含量和碳同位素组成的测量方法进行了研究,使用德国Finnigan公司DeltaPlusXP同位素质谱仪和GasBenchⅡ在线制样装置对实验室制备的四个实验室标准进行了反应流程、平衡时间、信号强度、数据精度、标准稳定性等检测,结果显示平衡时间大于4h检测信号达到稳定,同时发现44CO2信号强度和水样中溶解无机碳(DIC)浓度具有很好的相关性,因此可以利用信号强度来计算原样品中的DIC浓度。在四个实验室标准中,由NaHCO3配置的标准具有非常好的稳定性和精度,可以作为测试的工作标准。本方法测量水样中溶解无机碳的δ13C分析精度为0.1‰。本方法可以广泛应用于自然界各种水体中溶解无机碳(DIC)含量及其稳定碳同位素组成的分析。     

内陆水体溶解无机碳同位素研究进展及展望

碳是陆地生态系统中最重要的生命元素,能够在各个圈层之间相互转换和运移。碳循环作为地球各圈层相互连接的纽带,被认为是地表系统最重要的元素地球化学循环。碳在水体中主要以溶解性有机碳（dissolved organic carbon,简称DOC）和溶解性无机碳（dissolved inorganic carbon,简称DIC）形式存在。内陆水体（包括河水、地下水、湖水和水库等）尽管只占陆地表面1%,但它们在碳循环过程中发挥了重要作用。其DIC浓度(CDIC)和DIC同位素组成(δ13CDIC)可以为碳循环研究提供线索,因此成为近年来国际研究的热点之一。本文系统总结了全球内陆水体DIC同位素的研究进展。DIC同位素具有广泛的地质应用,不同碳源具有独特的同位素特征。因此,DIC同位素被用于定性和定量地示踪碳源,指示碳循环过程以及确定河水补给端元。     

Gas BenchⅡ-IRMS测定地下水中溴同位素新技术

建立了利用GasBenchⅡ联用同位素比值质谱仪（GasBench Ⅱ-IRMS）用于测定地下水中溴稳定同位素的方法。基于溴比氯更容易被重铬酸钾氧化的性质,将Br-氧化成Br2,而氯残留在原溶液中,从而把溴与氯分离开;再利用AgNO3将溴以AgBr的形式沉淀下来,然后将AgBr转化成CH。Br进行溴稳定同位素质谱测定。反应中,CHsI用量为20μL,AgBr用量为0．5mg。本测试流程需溴4～10mg,质谱测试时问由1．5h缩短为800s,测试精度优于±0．1‰（2σ）。该方法可以用于地下水中溴同位素测定,在水文地质研究中具有广阔的应用前景。     

海洋沉积物孔隙水中溶解无机碳(DIC)的碳同位素分析方法

海水中往往含有一定量的溶解CO2（以HCO-3存在），其δ13C值组成十分恒定，一般在0‰值附近。赋存在海底沉积物中的孔隙水往往含有比海水更高的溶解CO2含量，且其碳同位素组成变化极大。对这些溶解CO2的碳同位素组成进行分析，能够为我们了解海底沉积物沉积-成岩过程和生物地球化学过程提供十分丰富的信息。为此，开展了沉积物孔隙水中溶解CO2 (DIC)的碳同位素分析方法的研究。 采用的仪器为德国Finnigan公司生产的连续流质谱仪（Delta Plus XP）及与之联机的多功能制样装置(Gas Bench)。 Delta Plus XP为稳定同位素比值质谱仪，可以进行C、H、O、S、N等稳定同位素比值的测定，内精度小于0.1‰，外精度为0.1‰,稳定性好于0.03×10-6nA/h。Gas Bench为多功能在线制样装置，可进行CO2-H2O平衡法氧同位素，溶解二氧化碳碳同位素，碳酸盐碳氧同位素，空气中氮同位素及氮总量的前期制样，由于使用自动制样系统，具有处理时间短，效率高的优点。 样品分析过程：首先在自动进样器中对样品管进行烘烤(45℃)，然后拧紧瓶盖向样品管中充入氦气（16 min/管），充气完毕之后开始加人样品，使用注射器向管中注射0.5 mL样品，下一步使用加酸装置向管中注人磷酸反应平衡，磷酸用量大约0.3 mL左右，反应式如下： H3PO4＋HCO-3 aq===CO2(g)+H2PO- 4…+H2O…… 平衡1h后利用氦气将反应生成的气体CO2送人Delta Plus XP质谱仪测试。 实验过程中，制备了3个水样标准。NJWCS-l为直接取自实验室的Mill-Q纯净水，NJWCS-2为Mill-Q纯净水经蒸沸再冷却后，装人一密封的瓶子中，并向瓶中通人实验室用超纯钢瓶CO2气约4h，使CO2气充分溶解在水中并达到平衡。该瓶气体的δ13C值为-21.85‰。NJWCS-3为南京大学的自来水。 在不同时间对上述标准水样进行碳同位素组成测试结果表1。 实验过程中，选取3个采自南海北部某区海底沉积物孔隙水样品，进行了多次重复测试。结果表明，测试结果十分稳定。其中S-1的δ13C值（-5.11±0.12)‰( n=4); S-2的梦δ13C值（-27.13±0. 02)‰( n=2);S-3的δ13C值（-29.34±0.37)‰（n＝2)。 综上所述，通过笔者建立的分析方法，可对沉积物中孔隙水溶解无机碳碳同位素组成进行准确测试。这一方法的建立，有利于对海洋沉积物孔隙水中可能存在的碳同位素组成异常及其与天然气水合物的关系进行深人探讨。同时，该方法也完全适合于测定自然界中其他水体（如湖水、河水、油田卤水、地下水等）的溶解无机碳的碳同位素组成，因而该方法有着广泛的应用前景。     

激光光谱技术在溶解无机碳碳同位素分析中的应用

天然水溶解无机碳（DIC）碳同位素组成（δ13CDIC）分析是研究碳元素循环及相关生物地球化学过程的重要手段之一。近年来,激光光谱技术的发展为碳同位素比值测定提供了一种新的方法。文中阐述了一种总有机碳仪—激光光谱同位素仪联用在线测定水中DIC含量及δ13CDIC值的技术方法。该方法具有较高的测试精度,DIC含量测试结果相对标准偏差能控制在1%以内,δ13CDIC值精度优于±0.1‰（1σ）。不同类型岩溶水δ13CDIC值的测试结果与质谱仪法结果接近,差值总体≤0.3‰,表明该测试技术具有较高的准确度。由于吸收光谱信号与目标气体浓度有关,较低的CO2浓度会影响激光光谱仪的稳定性,在测试时需要根据DIC浓度控制样品进样量,最好采用多标样法来校准仪器测量值。激光光谱技术因其具有低成本、测试快速可靠,且仪器小巧便携等特点,在岩溶水溶解无机碳碳同位素分析中具有较大应用前景。     

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

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δ13CDIC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δ13CDIC值变化无规律且幅度大,而加了饱和氯化汞的水样δ13CDIC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δ13CDIC值逐渐偏重,主要受温度升高有利于HCO3-水解并释放CO2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δ13CDIC值较初始值偏重,混合水和非岩溶区水δ13CDIC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,δ13CDIC最大变化值为0.42‰;用顶空样品瓶采集的水样保存时间长,δ13CDIC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。      

重庆地区岩溶地下河水溶解无机碳及其稳定同位素特征

稳定碳同位素是指示岩溶动力系统碳来源及转化的重要指标。为揭示重庆地区岩溶地下水中溶解无机碳基本特征和碳来源,本文对该地区63条岩溶地下河水样进行了水化学和碳同位素分析。研究结果表明,重庆地区地下河水溶解无机碳主要表现形式为HCO3-,雨季由于稀释作用其浓度低于旱季。重庆岩溶地下河水δ13C-DIC（V-PDB）旱季变化范围为-15.34 ‰～-5.89 ‰,雨季变化范围为-17.40 ‰～-4.23 ‰。根据δ13C同位素质量平衡方法,计算得到重庆地下河旱季碳酸盐岩溶蚀对DIC贡献为45.1 % ～79.7 %,雨季平均为34.6 %～82.1 % 。计算结果表明,在人类活动不断增强的情况下,岩溶水体DIC通量中碳酸盐岩溶解来源的DIC和其参与岩溶地下水δ13C值的形成并不一定是岩溶作用理论方程中所计算的50 %,而是有一定的变化范围。因此在计算岩溶作用碳汇时,建议通过δ13C值扣除碳酸盐岩溶蚀形成DIC的通量后再来推算岩溶作用形成的碳汇量。     

北江河水溶解无机碳同位素的季节变化

在有碳酸盐岩分布的河流流域, 河水地球化学主要反映的是风化速率较高的碳酸盐矿物风化的信息, 而硅酸盐矿物风化的信息往往被掩盖掉.北江流域碳酸盐岩和硅酸岩分布广泛, 为追踪其中的硅酸盐矿物风化的信息, 分析了北江河水中溶解无机碳同位素的时空变化.河水样品按4个季节自北江的上游到下游采集6个样点, 分析结果显示, 除上游武江的采样点同位素值季节变化不大外, 中下游采样点的同位素值有明显季节变化, 主要表现在6月份的δ13C_DIC显著变轻(-16‰~-19‰).在详细剖析矿物风化过程对碳同位素的影响后, 指出除了显著的碳酸盐矿物风化过程外, 北江流域在夏季还存在明显的硅酸盐矿物风化过程, 大大提高了流域的碳汇作用.      

岩溶水库热结构变化对水体溶解无机碳及其同位素的影响过程

以中国南方亚热带地区典型的地下水补给型水库——大龙洞水库为对象,于2018年1月、4月、7月、10月、12月分别在上、中、下游三个监测点进行采样,探究水库热结构变化对于水体无机碳及其同位素的影响过程及机理。结果表明：（1）大龙洞水库水体在一个水文年中呈现周期性的混合期—分层期—混合期的热结构变化,4月热分层开始显现,7月逐渐显著呈现完整的热分层,10月以后热分层逐渐消失,水体逐渐实现混合;（2）水体热分层是溶解无机碳（DIC）浓度与碳稳定同位素（δ¹³C_DIC）值变化的主要驱动力。表水层中DIC主要受水—气界面二氧化碳脱气、水生生物光合作用控制,其DIC浓度与δ¹³C_DIC值分别为3.22 mmol·L⁻¹和−9.15‰;温跃层中DIC主要受有机质降解过程影响,其DIC浓度与δ¹³C_DIC值分别为3.43 mmol·L⁻¹和−9.70‰;底水层中DIC主要受碳酸盐沉淀过程影响,其DIC浓度与δ¹³C_DIC值分别为4.32 mmol·L⁻¹和−11.89‰;（3）三种过程伴随水库热结构的变化而变化,驱动DIC浓度及其同位素的变化梯度 G (DIC)与 G (δ¹³C_DIC)的变化,表现为底水层＜表水层＜温跃层。热分层结束进入混合期后,DIC浓度与δ¹³C_DIC值的时空差异均逐渐消失,最终表现出DIC浓度与δ¹³C_DIC值的均一化。     

土地利用变化对岩溶地下水溶解无机碳及其稳定同位素组成的影响

土地利用变化对岩溶地下水溶解无机碳（DIC）的影响关系到岩溶作用强弱及其相关的全球碳循环的正确评价。对贵州茂兰原始森林内的板寨岩溶地下河流域和普定岩溶石漠化强烈的陈旗、灯盏河泉域三种不同的土地利用下的地下水的DIC及其稳定同位素进行了分析,结果表明,地下水的DIC表现形式主要为HCO3^-。对于缺少土壤覆盖的板寨和灯盏河岩溶地区,雨季主要因为稀释作用,HCO3^-含量出现年内最低值;而对于较多土壤覆盖的陈旗岩溶地区,雨季主要受土壤CO2效应控制。HCO3^-含量出现年内最高值,反映了土壤在岩溶作用及其碳循环中的特殊重要性。此外,夏季由于生物量的增加,δ^13DIC值较冬季偏轻1‰～2‰。而对于不同土地利用而言,石漠化影响下的地下水δ^13DIC较原始森林下的地下水偏重2．5‰-3．0‰,且随着石漠化的发展,土壤的进一步流失,地下水δ^13DIC进一步偏重,反映了石漠化后生物量比例减少和大气成因CO2比例增加对地下水δ^13DIC升高的影响。     

Re-evaluation of linearity and precision of Gas Bench II-IRMS system and potential implications for carbon and oxygen isotope measurements on small-sized carbonate samples

In this study, the δ^13C and δ^18O values were systematically measured on NBS-18, NBS-19 and IAEA-CO-1 with different sample sizes, with the objective to examine the stability and reproducibility of previously developed linearity correction strategy especially for small-sized samples （e.g. 〈50 μg）. Firstly, the δ^13C and δ^18O values of NBS-19 standards （6-10 samples per run） with sample sizes scattered below -100 μg were determined in three different runs. The logarithmic regressions were performed on the plots of δ-values vs. peak area （sample size） for each run and the correction was applied using peak area of the first peak. Results show that two of the three data sets have almost the same regressive equations for both δ^13C and δ^18O values. The maximum difference in δ^13C values calculated by three equations when sample size varies between -10 and -100 μg is better than 0.15‰, compared with the maximum 0.82‰ for δ^18O values. Since alteration of phosphoric acids could not influence carbon isotope, the 〈0.15‰ difference in calculated δ^13C values should reflect the stability of mass spectrometer conditions. In contrast, the large difference in regressive equations for δ^18O values may be attributed to changed oxygen isotope in phosphoric acids due to exchange with atmosphere through time. It means that standards with sample sizes properly distributed should be arranged in every run for subsequent linearity correction of δ^18O values of small-sized samples （e.g. marine ostracode）.     

Diel behavior of stable isotopes of dissolved oxygen and dissolved inorganic carbon in rivers over a range of trophic conditions,and in a mesocosm experiment

Rates of diel (24-h) biogeochemical processes in rivers and their effect on daily changes in the concentration of metals and metalloids have been well documented in the literature over the last 20 years. Investigations into the effects of these processes on aquatic systems and the underlying mechanisms that control the processes can significantly improve our understanding of how natural aquatic environments function and will respond to changing environmental conditions and anthropogenic impacts. Daily changes in the rates of biogeochemical processes have, more recently, been shown to influence the stable isotope composition of dissolved oxygen and dissolved inorganic carbon in natural waters. Here we present a comprehensive picture of the persistence and reproducibility of diel cycles of the ¹⁸O composition of dissolved molecular oxygen (δ¹⁸O-DO) and the ¹³C composition of dissolved inorganic carbon (δ¹³C-DIC) across five Montana, USA rivers investigated over a 4-year period. A mesocosm experiment showed the same behavior in δ¹⁸O-DO and δ¹³C-DIC as seen in riverine settings across light and dark periods.A cross plot of δ¹⁸O-DO and δ¹³C-DIC from each stream exhibits a clockwise elliptical pattern which is attributed to the daily changes in the balance of metabolic rates as well as air–water gas exchange. The amplitude of the change in the isotope composition is shown to be directly related to the trophic state of the river and a relationship between net productivity and diel changes in δ¹⁸O-DO and δ¹³C-DIC is presented. This relationship between trophic status with δ¹⁸O-DO, δ¹³C-DIC and production emphasizes the significance of how rates of biogeochemical processes in natural systems can influence the daily changes in the composition of surface waters.     

硫酸侵蚀碳酸盐岩对长江河水DIC循环的影响

对长江及其主要支流河水水化学和溶解无机碳（DIC）同位素组成（δ13GDIC）进行了研究。河水阳离子组成以Ca^2＋、Mg^2＋为主,阴离子以HCO3-、SO4^2-为主,水化学组成主要受流域碳酸盐岩矿物的化学侵蚀控制。DIC含量为0．3～2．5mmol／L,从上游到河口逐渐降低。δ13CDIC值为-12．0‰-3．4‰,与DIC含量具有相似的变化趋势。H2CO3溶解碳酸盐岩是控制河水DIC来源及其占δGDIC组成的主要机制。H2SO4溶解碳酸盐岩加剧了流域碳酸盐岩的化学侵蚀,一方面导致了河水的DIC含量增加,另一方面也使河水的δ13GDIC值升高。     

Lithium isotopes in foraminifera shells as a novel proxy for the ocean dissolved inorganic carbon (DIC)

Past ocean pH and pCO₂ are critical parameters for establishing relationships between Earth's climate and the carbon cycle. Previous pCO₂ estimates are associated with large uncertainties and are debated. In this study, laboratory cultures of the foraminiferan genus Amphistegina were performed in order to examine the possible factors that control the Li isotope composition (δ⁷Li) of their shells. δ⁷Li is insensitive to temperature and pH variations but correlates positively with the Dissolved Inorganic Carbon (DIC) of seawater. Li/Ca ratio in the shells shows negative correlation with δ⁷Li, consistent with published data for planktonic foraminifera from core tops and from short periods during the Cenozoic. We propose that the sensitivity of δ⁷Li and Li/Ca ratio to DIC is a biological phenomenon and is related to biomineralization mechanisms in foraminifera. We used the published foraminiferal δ⁷Li records, and our experimental results, to determine the paleo-ocean DIC and pH for the last glacial–interglacial cycle. The results are consistent with published estimates of pH and pCO₂ based on boron isotopes and ice cores. We suggest Li and its isotopes may serve as a new complementary proxy for the paleo-ocean carbonate chemistry.     

A new method for analysis of osmium isotopes and concentrations in surface and subsurface water samples

We describe a new method for the determination of osmium (Os) content and ¹⁸⁷Os/¹⁸⁸Os isotopic ratio in water samples, particularly adapted to analysis of reducing waters such as groundwaters. The critical feature of the method is the improved oxidation step. We use a high pressure asher (HPA-S) to achieve oxidation of all Os species at high pressure (~ 130 bars) and high temperature (250 °C). A series of tests was performed on two groundwater samples in order to study the general behavior of Os during oxidation and to optimize the various parameters of the method. At high temperature (≥ 250 °C), using hydrogen peroxide as an oxidant, complete spike-sample equilibration and oxidation of Os species to the highest oxidation state (OsO₄) are obtained in less than 10 h. A strong contrast in oxidation behavior was observed between tests performed at high (250 °C) and low temperature (100 °C). The results for both samples indicate a difference in the oxidation kinetics between spike and sample. They also demonstrate that a non-negligible proportion of each sample is easily oxidized at low temperature whereas high temperatures are required to oxidize the rest of the sample. This last observation could provide evidence for the existence of several species of osmium in groundwater samples. Our results underscore the need for high temperatures to assure spike-sample equilibration and complete oxidation of all Os species potentially present in water. The method presented here, which is adapted to various matrices, opens the possibility of analyzing Os concentrations and isotopic compositions in groundwater and thus to better constrain the potential sources of osmium delivered to the ocean.     

单生卵囊藻对DIC的利用及其对CaCO3沉积影响的研究

以生长在钙华池中的单生卵囊藻（Oocystis solitaria Wittr）为研究对象,利用pH漂移方法,探讨了封闭系统中单生卵囊藻在岩溶水和非岩溶水环境下对溶解无机碳（DIC）利用及其对水体Ca^2＋沉积影响的差异。结果表明,单生卵囊藻在低CO2浓度时,通过胞外碳酸酐酶的催化,以HCO3^-作为无机碳源进行光合作用。在岩溶水环境下单生卵囊藻DIC利用能力要高于非岩溶水环境（4．78倍）,而在此过程中对水体中Ca^2＋沉积的影响也更高（2．13倍）。在岩溶水（非岩溶水）环境下,有42．6％（8．9％）的Ca^2＋通过物理化学效应以CaCO3形式沉积,其余Ca^2＋可能被藻体生长而吸收利用．．     

Behavior of stable isotopes of dissolved oxygen,dissolved inorganic carbon and nitrate in groundwater at a former wood treatment facility containing hydrocarbon contamination

The speciation and mobility of a variety of chemical species in groundwater are strongly influenced by redox and pH conditions. Dissolved O₂ (DO) and dissolved inorganic C (DIC) concentrations are significant controls of these conditions, respectively. It is not always clear what the major processes are that influence changes in the concentration of DO and DIC across a groundwater flowpath. The combined use of the stable isotope compositions of DO (δ¹⁸O–DO) and DIC (δ¹³C–DIC) has the potential to help investigators discriminate between sources and sinks of DO and DIC in groundwater systems.