湖泊有机质的来源与生物地球化学循环：稳定氮同位素示踪技术

氮循环是水生生态系统中重要的营养循环，对它的研究能够为水环境评价以及解决日益严重的湖泊富营养化问题中的氮治理提供理论依据。水体中的有机质分为颗粒态有机质(POM)和溶解态有机质(DOM)两部分，它们在水体中与无机氮相互转化、相互作用，共同控制着整个水生生态系统内部的氮循环过程。稳定氮同位素技术作为有效的地球化学工具能够被用于追溯水生生态系统中的物质来源以及指示相关的生物地球化学循环作用。因此对有机质稳定氮同位素比值的测定有利用帮助我们了解它在水生生态系统中所扮演的角色，尤其是得到有机质参与的地球化学循环作用的直接证据，从而进一步完善对水生生态系统内部整个氮循环过程的研究。 本研究首先从根本上解决了限制溶解有机氮(dissolved organic nitrogen，DON)稳定氮同位素比值应用的测定技术上的难题。然后选择贵州高原湖泊―红枫湖和百花湖作为研究对象，测定了2003~2004年两湖水体中颗粒态有机氮同位素比值(δ15NPON)的季节及剖面变化，探讨了两湖季节性变化存在差异的原因以及红枫湖纵向水体剖面上δ15NPON的变化规律及影响因素。最后，在前人对红枫湖研究的基础上重点选择了2006~2007年间湖泊热分层不同时期具有代表性的几个月份进行了剖面采样。测定了不同月份纵向水体剖面上的DON、PON与NO3-三种氮形态的含量、δ15N值以及其它水化学参数，揭示了水体内部氮循环过程中的相关生物地球化学作用。同时，结合冬季湖泊枯水期外源输入河流以及湖泊水体横向剖面上的DON、PON与NO3-三种氮形态的含量及其δ15N值的变化，追溯了湖泊水体中各种氮形态的来源以及外源输入河流对湖泊水体的贡献。本研究得到以下几点结论： 1. δ15NPON值的季节性变化可以用于评价水生生态系统的营养状况，指示外源人为活动产生的工业废水和生活污水的影响。对2003~2004年间红枫湖和百花湖两湖表层湖泊水体中PON的δ15N季节性变化研究表明，红枫湖表层颗粒态有机质δ15NPON的变化范围为+3.7～+14.9‰；百花湖颗粒态有机质δ15NPON的变化范围为+1.3～+8.7‰。其季节性变化趋势不同。红枫湖表现为冬季(2月)和夏末秋初(9月)出现高值；冬季高值的出现主要受外源输入的工业废水中富含15N的无机氮源和有机颗粒的影响。百花湖在冬季(2月)出现最低值，夏末秋初(9月)出现高值；冬季最低值的出现则可能归功于生活污水中富含14N的有机颗粒的贡献。 2. 首次从整体角度得到了δ15NDON值变化区间的信息。红枫湖2006~2007年不同采样月份水体内部的δ15NDON测定结果显示，δ15NDON的变化范围为+1.0~+12.3‰，它与δ15NNO3-的变化范围：5.9~+22‰和δ15NPON变化范围：+2.8~+16.8‰接近。同时，研究还发现在浮游植物生长季节，表层水体不同形态氮的同位素比值普遍存在下述规律：δ15NNO3->δ15NPON>δ15NDON。原因是此时浮游植物是PON的主要组成部分，且吸收利用NO3-的过程是δ15NPON变化的主要控制因素，浮游植物通过分泌细胞外液等方式分解产生了的富含14N的DON，从而使得三种形态的氮同位素具有一定的继承关系。 3. 三种氮形态δ15N值的季节性变化趋势能够反映其来源的差异。纵向剖面水体中，2007年1月的δ15NNO3-最大，湖泊受外源河流携带的高δ15N及高含量NO3-的影响。2006年4月和2007年3月的δ15NNO3-较小，水体内部发生的强烈的硝化作用产生了大量富含14N的NO3-，是湖泊水体NO3-的重要内源。δ15NDON值表现为：除2007年3月表现异常外(出现异常高值)，浮游植物生长季节(2006年4月和2006年7月)的 δ15NDON普遍小于其余月份，且纵向水体剖面上变化幅度均不太大，这与浮游植物生长季节DON主要来源于浮游植物分泌等作用产生的富含14N的组分有关。δ15NPON值表现为冬季(2007年1月)具有最高值，受外源输入河流中富含15N的有机颗粒的影响。 4. PON降解方式的不同可能引起生成的δ15NDON存在差异。PON在有氧条件下发生硝化降解时，由于富含14N的组分优先被释放，因此生成的DON组分的δ15N值较小，如2006年4月10m以上水体和2006年7月10m以上水体；而当PON在厌氧条件下发生反硝化降解时，富含15N的组分则优先被释放，从而使得生成的DON其δ15N较大，如2006年4月18m以下水体和2006年7月10m以下水体。 5. 纵向水体剖面上δ15NPON的显著变化来源于其组成的变化，并且不论是硝化细菌还是反硝化细菌，当它们作为PON的主要组分时均会造成δ15NPON的减小，如2006年7月和2007年3月中下部水体。 6. 三种氮形态同位素比值的结合能够更加有效地示踪有机质来源的变化。如2007年1月纵向水体剖面，整个水体剖面氮含量无明显变化，而氮同位素比值则有显著变化。20m处δ15NPON、δ15NNO3-和δ15NDON均在此发生转折，显示20m可能是外源输入与内部水体的分界层。此时，横向水体剖面上，采样点4处NO3-显著增加，而δ15NNO3-保持不变；δ15NDON显著减小。说明采样点4处可能有新的氮源出现。初步估计是由于先前网箱养鱼的积累影响还有高含量的NO3-，低δ15N值的DON输出。 以上的研究结果充分证实了有机质的稳定氮同位素比值的变化能够更加直接地用于追溯有机质的来源以及追踪有机质在湖泊水体中参与的生物地球化学循环作用。

提取湖泊碳酸盐碳同位素环境信息的理论模式的辨识不同源碳酸盐的实验技术

作者通过对淡水、分层、富营养湖泊光合作用对水体碳同位素组成影响的系统分析，对争论长达20年的， 湖水上层碳源问题从理论上和实测资料上绘出了一个有说服力的解释模式－“生物泵模式”。利用这种模式，有效地解释了大量预测到以前不能很好被说明的实测数据。作者提出和建立了辨识湖泊的同源碳酸盐的实验方法和实验交流。通过理论和实测数据的分解，说明了该实验系统的可行性和有效性。利用这种技术，提高了对碳酸盐同位系环境信息的分辨能力。

A study on the ignition process for the catalytic partial oxidation of methane to synthesis gas by MS-TPSR technique

The ignition processes for the catalytic partial oxidation of methane (POM) to synthesis gas over oxidic nickel catalyst (NiO/Al2O3), reduced nickel catalyst (Ni-0/Al2O3), and Pt-promoted oxidic nickel catalyst (Pt-NiO/Al2O3) were studied by the temperature-programmed surface reaction (TPSR) technique. The complete oxidation of methane usually took place on the NiO catalyst during the CH4/O-2 reaction, even with a pre-reduced nickel catalyst, and Ni-0 is inevitably first oxidized to NiO if the temperature is below the ignition temperature. It is above a certain temperature that Ni-0 is formed again, which leads to the start of the POM. The POM can be initiated at a much lower temperature on a Pt-NiO catalyst because of Pt promotion of the reduction of NiO. The POM in a fluidized bed can be easily initiated due to the addition of Pt.

On the evaluation of diffusivities in gels using the diffusion cell technique

Modeling of the gel-immobilized cell system requires accurate measurement of diffusion coefficients. Three methods of the quasi-steady-state (QSS) method, the time-lag (TL) method and a variant quasi-steady-state (VQSS) method were critically assessed and compared for the evaluation of diffusivities using the diffusion cell technique. Experimental data from our laboratory were used for the analysis of the influence of crucial theoretical assumptions not being fulfilled in each method. The results highlighted a risk in obtaining highly variable diffusion coefficients by not validating the QSS and the accuracy of the measurements. In the TL method, the estimation of diffusivities based on the plot intercept that was mostly used in the literature, results in a many fold lower value when compared to that based on the plot slope. The comparison with the QSS and VQSS methods confirmed similar diffusivity obtained by the TL method based on the plot slope. It thus suggested that the correct estimation of diffusivities by the TL method could be based on the plot slope only. Furthermore, the errors associated with the solute mass in the gel, the sample withdrawal and the non-negligible concentration changes in the chambers were also discussed. It is concluded that diffusion cell technique has to be employed cautiously for a correct evaluation of diffusivities. (C) 2001 Elsevier Science B.V. All rights reserved.

Drug-protein interaction studied by technique of microdialysis combined with high performance liquid chromatography

Drug-protein binding is an important process in determining the activity and fate of a pharmaceutical agent once it has entered the body. This review examines the method of microdialysis combined with high-performance liquid chromatography (HPLC) that has been developed;by ours to study such interactions, in which the microdialysis was applied to sample the free drug in the mixed solution of drug with protein, and HPLC to quantify the concentration of free drug in the microdialysate. This technique has successfully been used for determining various types of binding interactions between the low affinity drugs, high affinity drugs and enantiomers to HSA. For the case of competitive binding of two drugs to a protein in solution, a displacement equation has been derived and examined with four nonsteroidal anti-inflammatory drugs and HSA as model drugs and protein, respectively. Microdialysis with HPLC was adopted to determine simultaneously the free solute and displacing agent in drug-protein solutions. The method is able to locate the binding site and determine affinity constants even up to 10(7) L/mol accurately.

Application of liquid pre-column capillary electrophoresis technique to the study of interaction between drug enantiomers and human serum albumin

Based on the chiral separation of several basic drugs, dimetindene, tetryzoline, theodrenaline and verapamil, the liquid pre-column capillary electrophoresis (LPC-CE) technique was established. It was used to determine free concentrations of drug enantiomers in mixed solutions with human serum albumin (HSA). To prevent HSA entering the CE chiral separation zone, the mobility differences between HSA and drugs under a specific pH condition were employed in the LPC. Thus, the detection confusion caused by protein was totally avoided. Further study of binding constants determination and protein binding competitions was carried out. The study proves that the LPC technique could be used for complex media, particularly the matrix of protein coexisting with a variety of drugs.