重量法测定土壤水溶性盐总量的优化

土壤水溶性盐是表征土壤盐碱化程度的重要指标,也是评价耕地地力的重要参数,被纳入第三次全国土壤普查（“三普”）监测指标体系中。重量法是测定土壤水溶性盐总量的最常用方法,其测定过程易受多种因素影响,导致其测定结果不准。鉴于此,本文设计试验分别验证了水溶性盐浸提和浸提液固液分离这两个过程对测定结果的影响,结果表明浸提液固液分离是影响土壤水溶性盐总量测定准确度和精密度的主要因素。基于此进一步探究4种不同固液分离方式（布氏漏斗过滤、滤膜真空抽滤、离心、滤纸组合过滤）对测定结果的影响,结果表明相较于其它方式,滤纸组合过滤测定结果准确度高,适用于土壤水溶性盐总量的测定。对改进后的重量法测定土壤水溶性盐总量进行方法学确认,结果表明其检出限为0.01 g/kg,测定下限为0.04 g/kg;方法的准确度和精密度、适用范围等均符合相关要求。本文推荐的土壤水溶性盐总量测定方法为：土壤样品采用1:5土水比浸提,180 r/min振荡3 min,浸提液采用滤纸组合自然过滤;其测定结果的准确度和精密度符合相关要求。本文旨在为“三普”内业检测提供参考和借鉴,为全面摸清不同区域土壤水溶性盐含量水平及土壤盐渍化程度提供技术支撑。     

土壤中有效硼含量测定方法优化与对比

为确保第三次全国土壤普查数据真实可靠,需对相关标准检测方法进行反复验证以优选出适合在全国范围内推广的方法。目前NY/T 1121.8-2006甲亚胺-H比色法测定土壤有效硼灵敏度较低,显色温度及光照等因素容易对测定结果造成干扰。鉴于此,本文对沸水浴浸提-甲亚胺-H比色法测定土壤有效硼过程中的浸提时间、浸提方式以及显色条件等关键因素进行了分析,并探究方法测定优化条件。结果表明提取时间选择12 min、加盖浸提以及23 ℃避光显色处理,可以较好地减少有效硼测定过程中的误差,获得更为准确的结果。同时对电感耦合等离子体光谱法（ICP-OES）测定土壤有效硼进行了验证,比色法、ICP-OES法的检出限分别为0.012 mg/kg、0.009 mg/kg,均满足分析测定的要求。方法准确度和精密度验证结果表明二者均可用于土壤有效硼的测定,并且实际样品测定结果无显著性差异。其中,比色法适用于测定高含量（>0.5 mg/kg）样品,ICP-OES法适用于中、低含量样品的测定。结合第三次全国土壤普查内业检测定点工作中的经验,本文建议将ICP-OES法作为第三次全国土壤普查有效硼测定的首选方法,以期为“三普”内业检测提供参考和借鉴。     

ICP-MS法测定土壤中有效态砷的研究

分别以等离子体质谱法和原子荧光法,测定了国标土壤样品中有效态砷的含量,研究了两种方法的准确度;对等离子体质谱测定方法做消除基体干扰的对比研究。两种方法的测定值均在土壤样中有效砷的允许误差范围内,ICP-MS法的检出限为2.8 ng/g,精密度(RSD)在10％以下,符合分析测定要求。     

悬浮液进样石墨炉原子吸收法测定土壤中铋

对于微、痕量元素分析中的试样分解、分离技术和检测手段既要求方法简捷、测试灵敏,并要求分解试样中减少元素污染和损失。其中悬浮液进样石墨炉原子吸收法是很有前途的分析技术,但用于铋的测定未见报道。本文使用悬浮液进样,试样粒度不超过50μm。用铵盐作基体改进剂较有效地解决石墨炉中的基体干扰。本文采用1.5g·L~(-1)磷酸三铵作为土壤中铋的测定基体改进剂。方法不经试样分解、分离等步骤,快速、灵敏、准确测定土壤中微、痕量铋,对有代表性的风化土壤样分析,结果令人满意。     

电感耦合等离子体发射光谱（ICP-OES）法测定石灰性土壤中交换性盐基K+、Na+、Ca2+、Mg2+

石灰性土壤的交换性盐基常规检测方法过程手续繁琐、消耗乙醇量大、交换液过滤淋洗定容至250 mL容量瓶耗时过长。通过改变取样量和氯化铵-乙醇交换液的比例关系,选择合适的震荡时间,一次性交换完全,直接干过滤部分提取液到25 mL比色管中,再将滤液转移至聚四氟乙烯烧杯中,电热板加热挥发掉乙醇,用盐酸提取,使得乙醇体系转换为盐酸体系。该方法减少了乙醇的用量、缩短了前处理时间、解决了等离子体引入有机物熄火的问题,建立了电感耦合等离子体发射光谱（ICP-OES）法直接测定石灰性土壤盐基K+、Na+、Ca2+、Mg2+的方法。选用4个石灰性土壤有效态国家一级标准物质按照本方法进行处理,测定结果均在认定值的误差范围内;采用8个全国第三次土壤普查实际样品与标准方法进行比对实验,各组分检测结果无显著差异。各元素的光谱强度在0～100 μg/ mL浓度范围内呈良好的线性关系,相关系数（r）均在0.999 9以上,方法检出限值为0.004～0.015 cmol/kg,相对标准偏差RSD（n=12）为0.74 %～8.52 %。满足第三次全国土壤普查全程质量控制规范中对石灰性土壤基盐检测质量技术要求。     

土壤中铅的含量及其化学形态分析

对广州市黄埔港区所取土壤中铅的化学形态分析进行了研究。采用含不同组分提取剂的连续提取程序对1 g土壤进行提取,使之分成8种形态的铅,并用火焰原子吸收光谱法(FAAS)对每种提取所得的形态中的铅进行了测定。另在一份试样中直接测定其总铅量,对提取剂的组成及其溶液的浓度及提取操作条件进行了研究和优化,对FAAS测定方法的仪器工作条件作了说明。试验结果表明,所取试样中大部分铅以稳定的结合形态存在,以可交换态和碳酸盐结合态存在的铅仅达6%,总铅量随土壤深度的增加而减少。FAAS测定方法的灵敏度和检出限依次为0.007 mg.L-1及0.01 mg.L-1,分析和测定了4个试样中8种形态的铅量,其加和量为147.9 mg.kg-1,与直接测得的总铅量(159.9 mg.kg-1)之间的偏差小于10%。     

不同因素对柠檬酸浸提-硅钼蓝比色法测试土壤有效硅的影响及优化措施

准确测定土壤中有效硅含量可以了解土壤硅素肥力状况,有助于指导施肥、改善土壤质量。同时土壤中有效硅含量作为第三次全国土壤普查必测的一项参数,有利于全面摸清土壤硅的含量水平。文章通过改变浸提方式、浸提剂浓度以及显色方式等参数对柠檬酸浸提-硅钼蓝比色法测试土壤有效硅进行了探讨,对测试过程中的影响因素进行了分析,并进行针对性的优化 ,最后对改进后的测试条件进行方法学研究。结果表明,浸提时间不足、浸提剂浓度偏低以及显色时温度不稳定均会导致所测的有效硅含量偏低。采用连续震荡2h的方式浸提,同时增加浸提剂浓度为0.050mol/L,显色过程全程于35℃水浴中操作等措施可以较好的减少上述因素导致的误差,获得更准确的结果。改进后的方法线性良好,相关系数r为0.9996,检出限为1.0mg/kg,精密度RSD（n=6）最大为2%,准确度相对误差最大为-4.7%。测定结果可靠,可以为第三次全国土壤普查内业检测提供参考和借鉴。     

气相分子吸收光谱法和分光光度法测定土壤中氨氮的比较

对气相分子吸收光谱法和分光光度法的分析结果进行了对比。分别采用这两种方法对6种不同区域的土壤进行氨氮含量的测定,通过样品标准偏差、回收率和操作步骤的繁琐程度对两种方法进行了比较。研究结果表明:与分光光度法相比,气相分子吸收光谱法在测定土壤中氨氮时,实验步骤简单,分析速度快、消耗的实验试剂较少,精密度、准确性更高,更能胜任实验样品较多时的实验任务。     

测定土壤中重金属元素的样品消解方法

探讨适用于重金属分析的土壤样品处理方法。利用原子吸收光谱法测定土壤中Cu,Mn,Ni,Pb和Zn 5种元素的含量,对电热板、微波和水浴3种消解方法进行比较,结果表明:3种样品预处理方法的检出限、准确度和精密度均满足分析检测要求。其中,电热板法样品消解较彻底,Cu和Pb的测定结果准确,但试剂、时间和人力消耗多,且为敞开式消解,高温及产生的大量酸雾危害环境与健康;微波法为密闭式消解,样品和试剂用量少,耗时短,自动化程度高,消解彻底,安全环保,Mn的测定结果准确,但成本高,不适于大批量样品分析;水浴法为半封闭式消解,简单易行,Ni和Zn的测定结果准确,但消解剂中不含氢氟酸,不适于含有大量硅酸盐样品的处理。     

盐酸消解-原子荧光光谱仪测定土壤中总汞

本研究利用原子荧光光谱仪,探寻适合本实验室测定土壤总汞的方法。实验中对沸水浴消解和电热板消解这两种土壤样品的前处理方法、消解液种类以及仪器检测等因素进行条件试验,结果表明：土壤样品选用(1+1)盐酸溶液在沸水浴下加热消解、在热汞条件下分析待测液中的总汞含量是最佳样品消解及测定方法,该方法标准曲线的相关系数大于0.999,仪器最低检出限为0.006μg/g,精密度为1.2%~4.8%(n=7),样品准确度满足标准土样的要求。该方法快速简单,空白背景低,样品精密度准确度较高,适用于土壤中总汞的测定。     

Photopyroelectric method

High resolution measurements have been performed with a photopyroelectric (PPE) technique to study the static and dynamic thermal parameters behaviour in the critical region of different liquid and solid samples. In particular the specific heat (c), the thermal diffusivity (D) and the thermal conductivity (k) have been simultaneously determined in the critical region around the antiferromagnetic/paramagnetic (AP) phase transition occurring in FeF₂ and around the Smectic-A/Nematic (AN) phase transition occurring in the 8S5 liquid crystal.The high resolution of the measuring technique has allowed the determination of thec andD critical exponents and amplitude ratio of their critical terms.     

A quotient method of evaluation for the catalytic-kinetic difference method

A new variant of the catalytic-kinetic difference method is presented.The course of a catalyzed reaction, which proceeds simultaneously in two mixtures containing different catalyst concentrations, is followed by photometry. The maximum of the difference in transmittance being measured is a function of the quotient of the catalyst concentrations in the two mixtures and is independent of the rate constant. With this method of evaluation, a single calibration graph suffices for the determination of two different catalysts activating the same reaction. The maximum of the difference in transmittance is independent of temperature. The reaction between cerium(IV) and arsenic(III) catalyzed by iodide or osmium serves as an example. Two further examples are mentioned.     

Practical method validation: Validation sufficient for an analysis method

Validation of an analysis method depends on the purpose of the method, the chosen technique and the procedure in question. Methods are used for different research, product development, process control and quality control purposes. The human and economical importance of results vary. Each of the techniques used, such as chromatography-(HPLC, HRGC, TLC), capillary electrophoresis-(CE), spectrophotometry-(UV/VIS, IR, fluorescence, AAS, ICP) or spectrometric techniques (NMR, MS) as well as the hyphenated methods, have their own special features and deficiencies which must be considered. The method can include a simple pretreatment or it may include many demanding steps, it can use automation and data processing in various ways, it can have an official status, it can be a thoroughly verified or less studied one. How should these differences be accounted for during the validation? What would be a sufficient certainty that the method does what is expected, that the method fits for the purpose it was intended? The client (or authority) decides the required timetable, cost and quality level. This is why within a laboratory different quality levels and associated levels of validation exist. This paper tries to outline a practical test frame for validation efforts to assist the analyst when planning validation of a method.     

Advanced isoconversional method

A nonlinear algorithm has been suggested to increase the accuracy of evaluating the activation energy by the integral isoconversional method. A minor modification of the algorithm has made it possible to adapt the isoconversional method for an arbitrary variation of the temperature. This advanced isoconversional method allows for trustworthy estimates of the activation energy when the thermal effect of a reaction makes the temperature of a sample deviate from a prescribed heating program.     

Improved tight-binding method

An improved tight-binding method, taking into exact account the kinetic energy oerator, is proposed. The potential part of the Hamiltonian is represented by its matrix elements on some set of localized functions (like the LCAO method). The spectrum and the density matrix are determined by means of solving the nonlinear eigenvalue problem. © 1994 John Wiley & Sons, Inc.     

Comprehensive method based on model free method and IKP method for evaluating kinetic parameters of solid state reactions

This article presents, firstly, a short review of methods for evaluating kinetic parameters of solid state reactions and a critical analysis of the isoconversional principle of model free methods. It shows theoretically that the activation energy for complex reactions is not only a function of the reaction degree but also of heating programs, and points out that any method that attempts to extract the dependences of activation energy on conversion degree without considering the dependences of heating programs is problematic. Then an analysis is given of the invariant kinetic parameters (IKP) method and recommends an incremental version of it. Based on the incremental IKP method and model free method, a comprehensive method is proposed that predicts the degree of the dependences of activation energy on heating programs, selects reliable values of activation energy and extracts the values of variable pre‐exponential factor. This comprehensive method is tested using both simulation data and experimental data, the results of which show it can not only give reliable values of kinetic parameters but also be helpful in explaining inconsistencies of kinetic results in solid state reactions. © 2012 Wiley Periodicals, Inc.