基体改进剂在石墨炉原子吸收中的应用.doc

前言自从四年前引入石墨炉原子吸收分析法以后，在许多实验室中已经发展成为一种常规的分析方法。石墨炉法重要的优点之一就是对许多药品不需特殊的制备。通常液体药品可不用预处理直接注入石墨炉。然而，有时机体与分析物相结合，尤其是低挥发的基体组分或高挥发性的分析物，在灰化阶段即要分离基体干扰又要使分析物不挥发几乎是不可能。对这些复杂样品的分析有时可将一种简单的试剂加入到样品中直接注入石墨炉，使其在干燥或灰化阶段改变其化学性质。在石墨炉原子吸收法中把这些化学操作统称为“基体改进”。基体改进剂常具有一个或两个目的：（1）降低分析物的挥发以避免在灰化阶段的损失；（2）提高基体的挥发以促进它在原子化之前被消除。第1章 石墨炉原子吸收分析中的基体改进技术1.1 基体改进技术的应用范围石墨炉原子吸收分析一般比火焰原子吸收分析的绝对灵敏度高3个数量级，现已广泛应用于农业、生物、环境、食品、地质、工业和冶金等领域。但是石墨炉原子吸收分析尚存在许多干扰问题，特别是生物和环境样品中痕量金属元素的测定中，基体干扰还很严重。关于控制和消除干扰的方法，概括起来主要有背景校正技术、石墨管改进技术、预分离富集技术、基体改进技术等，这些技术均可在一定范围内不同程度地消除基体干扰，提高分析灵敏度和改善分析精确度。石墨炉原子吸收分析测定基体复杂的生物和海水样品中易挥发的金属元素时，背景吸收和灰化损失将严重干扰测定。如果待测元素和基体成分挥发性差别较大时，可采用选择性挥发技术。但若挥发性相近或共挥发，则需要采用由Ediger于1973年提出的基体改进技术1。所谓基体改进技术，就是往石墨炉中或试液中加入一种化学物质，使基体形成易挥发化合物在原子化前驱除，从而避免待测元素的共挥发；或提高待测元素的挥发温度以防止挥化过程的损失。12基体改进剂的类型Ediger首先提出了Ni(NO3)2和NH4（NO3）2等无机试剂可作为基体改进剂用于石墨炉原子吸收测某些金属元素以来，随着人们在分析中不断试验应用，到目前，基体改进剂约有60余种。它们可分为无机试剂、有机试剂、和活性气体3种类型。121 无机改进剂 该类基体改进剂主要有铵盐、无机酸、金属氧化物和金属盐类。如NH4NO3、(NH4)2SO4、NH4H2PO4、HNO3、H202、硝酸锂、硫氢化钾、高锰酸钾、Pd、Pt、La、Mo、Ag等三十几种，上述基体改进剂已用于诸如As和Se2、Pb和Cd3，Bi和Ge4等约20种元素的测定。122 有机改进剂某些有机试剂已作为基体改进剂用于石墨炉原子吸收分析。常用的有抗坏血酸、EDTA、硫脲、草酸、酒石酸、柠檬酸等十几种。这些基体改进剂已分别用于下述元素Sn5、Pb、Cd、Cu、Mn、Zn6等20余种元素的分析。123活性气体改进剂为促使基体在灰化过程中烧尽，改善待测元素的热稳定性，防止待测元素的缔合等化学干扰，向石墨炉中通入一定量的活性气体可取得一定的效果。13基体改进的机理孙汉文7总结出了基体改进主要通过以下几条途径降低干扰：(1)使基体形成易挥发的化合物来降低背景吸收。氯化物的背景吸收干扰，通常借助硝酸铵来控制，因为在石墨炉内发生下述化学反应：NH4NO3+NaClNH4Cl+NaNO3表l中列出了该反应相关的4种化合物的熔点和沸点。表1反应物和反应产物的熔沸点()化合物NaClNH4NO3NaNO3NH4Cl熔点801170307335（升华）沸点1431210（分解）380（分解）从表l的数据可以看出，基体改进后形成的硝酸钠，氯化铵及过剩的硝酸铵，在低于400都能蒸发。(2)使基体形成难解离的化合物。试样中过量氯化物对待测元素的吸收产生的化学干扰大多是由于形成了较易挥发但是在气相中解离不完全的待测元素氯化物造成的。其决定性因素是氯化物的稳定性。Lvov8研究了LiN03对0.1%介质中铊1微克吸收抑制效应的释放作用，结果列于表2中。表2 LiN03对铊吸收抑制效应的释放作用NaCl浓度/%LiN03浓度/%Tl的吸光度000.2550.100.0060.130.1800.150.2000.170.2200.1100.215050.260表2数据说明，当无LiN03存在时铊的吸收信号完全被NaCl抑制，随着LiN03浓度增大吸收信号逐步恢复到用纯铊溶液达到的水平。加入基体改进剂的作用是使解离能较少而干扰较大的基体NaCl以转变为解离能较大而干扰较少的氯化锂。(3)使分析元素形成易分解的化合物。Lvov8认为石墨管中碳是主体元素。他利用原子化出现温度Tapp值推测，Li、Na、K、Rb等27个元素存在着稳定的碳化物，稳定的碳化物的生成使得记忆效应大，原子吸收峰低而宽。对于易形成难熔碳化物的元素，可加入某种试剂与分析元素形成比较易熔易分解的化合物，降低原子化温度。基于防止分析元素碳化物的形成，钙可用来提高Ba、Be、Si、Sn的灵敏度。这给测定易形成热稳定碳化物的元素创造了一条途径。(4)使分析元素形成热稳定的化合物。石墨炉原子吸收测定易挥发金属元素的主要困难在挥发损失和背景吸收干扰。灰化温度高，易导致分析元素损失；灰化温度低，基体烧不尽造成在石墨炉内产生分析元素与基体成分的时间重叠。镍可以稳定多种易挥发的金属元素。镍可以把硒的允许灰化温度从300提高到1200，其原因由于生成热稳定的硒化物2。(5)使分析元素形成热稳定的合金。加入某种熔点较高的金属元素，与易挥发的待测金属元素在石墨炉内可形成热稳定的合金，因此提高了原子化温度和最高允许灰化温度。(6)形成强还原环境。一些熔点较高的金属元素与易挥发的元素生成热稳定的化合物和合金，可以提高原子化出现温度和允许灰化温度，防止分析元素灰化损失。而某些有机试剂具有降低原子化出现温度和原子化峰值温度以及允许灰化温度。原因在于有机试剂的加入改变和改善了待测元素原子化的历程。如何实现低温原子化，使待测元素的原子吸收信号与基体成分所引起的背景吸收信号相分离，已引起人们的兴趣。(7)改善基体的物理性质。这一基体改进方法包含两层含义：其一是针对碱金属和碱土金属对分析物的包藏而产生的干扰，解决方法是加入过氧化钠作基体改进剂。过氧化钠能产生氧气炸裂基体的结晶，其氧化作用对消除基体干扰也起定作用。例如在没有过氧化钠存在时铜在石墨铊的吸收炉内生成了绿色的氧化铜，而当过氧化钠存在时，氯化铜溶液干燥后生成了黑色的氧化铜。氧化铜因分子较大和难熔不易进入氯化物结晶而减弱了包藏引起的干扰。另一层含义是加入一种有机试剂，使溶液表面张力下降，从而改善了基体与炉壁的热接触，结果促进了基体的热分解，这或许就是许多有机试剂具有相同的基体改进效应的原因。 第2章 基体改进技术的应用21无机基体改进剂的应用211应用无机酸作为基体改进剂文献9应用无机酸来降低碱金属氯化物的干扰。且指出过渡金属氯化物的干扰。可用高沸点的酸来控制。HNO3可降低氯化物对铅的干扰，这是由于生成的HCl在干燥灰化过程中易被除去，而生成的硝酸钠背景吸收很小。另一方面硝酸的加入使铅转变成氧化物而避免了生成挥发性氯化铅和二氧化铅所引起的挥发损失。H3P04和H2SO4,之所以可消除氯化铜对铅镍的干扰，是因为生成的HCl易挥发除去之外，生成的磷酸盐和硫酸盐的背景吸收很小。何金兰等考察了HCl、硫酸、硝酸 、亚硫酸及硼酸中的锡的石墨炉原子吸收特性，发现硼酸是一种较好的基体改进剂。212铵盐作基体改进剂用铵盐作基体改进剂的报道已见诸于许多文献中，张宁10以磷酸二氢铵为基体改进剂，不经消化处理，直接测定全血中的Pb、Cd。陈淑怡11采用硝酸做基体改进剂标准系列加氯化钠，解决基体的化学干扰，不需要消化样品，可直接测定尿中镉。郑衍生12等利用EDTA铵盐做基体改进荆，全热解石墨管石墨炉原子吸收直接测定河泥中痕量锶。213以高熔点金属元素为基体改进剂 姚金玉13等采用镍和钯混合液做基体改进荆，不需要分离样品基体，采用平台石墨炉法直接测定高温镍基合金中硒，镍钯混合液使灰化温度和原子化温度分别提高200。孙汉文14对Pt、Pd、Au在分析铅过程中基体改进效果进行了研究，指出加入微克量的Pt、Pd、Au，水溶液中的铅最高允许灰化温度分别提高到1200、1150和850。文献15采用钯为基体改进剂使锗的灰化温度提高到1400，成功地测定了灵芝中的痕量锗。22有机基体改进剂的应用有机试剂的基体改进机理在于使石墨管内金属氧化物被有机物的热分解产物还原为金属，石墨炉内还原气氛的增强加速了金属氧化物的还原，致使待测元素原子化温度下降，避开了高温原子化时基体蒸发面产生的背景吸收干扰。文献16用磷酸氢二铵吐温80作为基体改进剂石墨炉原子吸收法直接测定全血样品中的铅，收到满意的效果。抗坏血酸作基体改进剂已用于石墨炉原子吸收直接测定海水中的Cu、Co、Mn17。Dolinse 18等人研究指出，加入mg/ml EDT有助于石墨管内的还原反应，可将Cd .Zn、Pb、Ag的原子化温度明显地向低温位移。硫脲和柠檬酸已作为基体改进剂用于铅和锌的直接测定。柠檬酸可消除氯化镁对测定锌的干扰。23活性气体改进剂的应用文献19在灰化阶段往石墨炉内气体中掺入适量的氧气，可降低原子化阶段的光散射与分子吸收干扰。氧气的掺入将促使有机物的氧化，使有机物气体在灰化阶段完全烧尽。文献20研究指出钢铁中的铅在没有氧气存在时，铅以氯化物的形式挥发，如果通入适量的氢气，则由于生成了极易挥发的氯化氢从而避免了铅的挥发损失。第3章 基体改进技术的发展方向由于基体改进技术的上述作用，得到了越来越多的分析工作者的推广和深入研究，使某些元素的分析灵敏度得到了很大提高，并改善了分析精度。然而目前对于基体改进效应机理方面的研究尚不多，一般只停留在方法的试验及使用上，更谈不上有成熟的理论来解释众多的基体改进效应。笔者认为，今后这一工作的方向将从以下几个方面加以突破：(1)利用新的物理及化学理论，借助其它分析手段研究石墨炉内基体改进效应作用机理。杨凡源21等用气相色谱法分析了柠檬酸在石墨炉内的热解产物。实验证实，柠檬酸在石墨炉加热过程中的热解产物主要是甲烷、氢气、一氧化碳以及新生碳等还原性物质。还原气体的增强则加速了金属氧化物的还原致使待测元素原子化温度下降。随着分析研究的不断深入，其它的分析手段诸如发射光谱法、X射线荧光法等都将为基体改进技术插上翅膀。 (2)简化石墨炉原子吸收分析的分析过程，基体改进技术将扮演重要角色。石墨炉原予吸收分析的样品前处理以及干燥、灰化、原子化、清洁等程序使其分析流程加长，固体进样、悬浮物进样及省掉某些升温程序的研究将会使石墨炉分析的应用前景大大拓展，而所有这些方法的应用都离不开基体改进剂的使用。宣维康22采用塞曼背景校正的仪器以硝酸为基体改进剂在铁基样品中分析嵌、镉、镍3个元素初步证明了缩短干燥时间和取消灰化阶段在冶金分析的可行性。赵泰等23用直接固体进样法，用1g/L钯和lg/L钽盐的溶液作为基体改进剂成功测定了混纺棉纱(90棉+10聚酯)中的磷含量。(3)基体改进技术与溶剂萃取相结合，分析生物和环境样品中痕量易挥发金属元素。经有机相萃取后的体系，大大减少了干扰元素的存在量及种类，这使基体改进剂更能有效地发挥作用。(4)试制专用含有基体改进剂的石墨管。借助贵金属元素进行基体改进分析的例子前面已讨论过，在石墨管内壁涂覆基体改进剂的渡层是进行基体改进分析的一条便捷途径。石墨管改进技术与基体改进技术相结合将为石墨炉原子吸收分析开辟广阔前景。(5)基体改进剂的应用，使石墨炉原子吸收分析范围拓宽至有机领域。周秋香24等采用Pd-Rb化学基体改进剂，建立了GFAAS间接测定氨基酸的新方法。谢 辞感谢*老师指引我们的论文的写作的方向和架构，并对本论文初稿进行逐字批阅，指正出其中误谬之处，使我们有了思考的方向。在此，谨向*老师表示崇高的敬意和衷心的感谢！谢谢*老师在我们撰写论文的过程中给与我的极大地帮助。 同时，论文的顺利完成，离不开其它各位老师、同学和朋友的关心和帮助。在整个的论文写作中，各位老师、同学和朋友积极的帮助我查资料和提供有利于论文写作的建议和意见，在他们的帮助下，论文得以不断的完善，最终帮助我们完整的写完了整个论文。 另外，要感谢在大学期间所有传授我们知识的老师，是你们的悉心教导使我们有了良好的专业课知识，这也是论文得以完成的基础。 感谢所有给我们帮助的老师和同学，谢谢你们！ 通过此次的论文，我们学到了很多知识，跨越了传统方式下的教与学的体制束缚，在论文的写作过程中，通过查资料和搜集有关的文献，培养了自学能力和动手能力。并且由原先的被动的接受知识转换为主动的寻求知识，这可以说是学习方法上的一个很大的突破。在以往的传统的学习模式下，我们可能会记住很多的书本知识，但是通过毕业论文，我们学会了如何将学到的知识转化为自己的东西，学会了怎么更好的处理知识和实践相结合的问题。 在论文的写作过程中也学到了做任何事情所要有的态度和心态，首先做学问要一丝不苟，对于发展过程中出现的任何问题和偏差都不要轻视，要通过正确的途径去解决，在做事情的过程中要有耐心和毅力，不要一遇到困难就达退堂鼓，只要坚持下去就可以找到思路去解决问题的。而且要学会与人合作，这样做起事情来就可以事倍功半。 总之，此次论文的写作过程，我们收获了很多，即为大学*年划上了一个完美的句号，也为将来的人生之路做好了一个很好的铺垫。 再次感谢我的大学和所有帮助过我并给我鼓励的老师，同学和朋友，谢谢你们！参考文献1:R D Ediger,Perkin-Eimer Absorption Application Study nmer，1973.5502:R D Ediger,At Absorpt newal，1975.14:1273:龙仁俊等.环境科学与技术，1992.(1):344:宣维康.分析化学，1992,20(2):345:蔡伯圣等，冶金化学，1992,12(3):236:R Guevremont,Anal chem，1980,52:15747:孙汉文，分析化学译刊，1987,9-12:2798:B V Lvov,Spectrchim Anal chem，1978,50:29:E J Czobik,JP Matousek,Anal chem，1980,50:210:张宁，光谱仪器与分析，1991,11(6):611:程淑怡，光谱学与光谱分析，1991，11(6):6112:郑衍生等，岩矿测试，1992,11(3):23613:姚金玉等，分析化学，1993，21(7):84614:孙汉文，中国科学院环境研究所研究生论文，198115:陈则树，分析化学，1991,19(2):140516:丁耀伟，光谱实验室，19918(4,5);12917:D J HYDES,Anal 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Seawater used in the determination of zinc in zinc-sensitive lines at 3076 to study a variety of salts in seawater interference. The experimental results show that sodium chloride, potassium chloride, sodium sulfate, calcium chloride magnesium chloride in particular, to inhibit zinc. Adding citric acid to eliminate these disturbances, generated by atoms of hydrogen chloride in the tube before escaping, magnesium citrate magnesium into heated and no longer interfere with the recovery of zinc to 10 of a 20% to 95% , the proposed method is suitable for water content higher than lx10-Og / l zinc were determined. The results with the results of anodic stripping law in line with ten times the standard deviation for the determination of 3.4-7.1%. 2. Soil mercury study of the direct determination of ascorbic acid with citric acid, EDTA hydrochloride as amine, organic reagents such as oxalic acid to reduce the mercury atoms of the role of temperature. Lemon twist in which the background value as a result of low-acid, not vulnerable to the effects of the matrix, for the most suitable for matrix modifier. In the presence of citric acid, mercury at 400 on the atoms of a complete, no citric acid to lower than 500 . At this point, the soil matrix, only a small portion of the volatile, the background absorption can be fully deducted from vapor lamp. Plus ion investigated the effects of mercury on the determination results show that soil ions no significant interference. Standard addition method using an analysis of soil samples, analyze results and the cold vapor atomic absorption spectrometry results. Determination of mercury in the capacity of 0.028 and 0.046 ADPL g / g soil samples, the determination of ten times the relative standard deviations were 6.8% and 5.6%, applicable to direct analysis of mercury greater than 20 ADPL g / g of soil samples do not need any chemical treatment. Similar methods have not yet found in the literature. 3. Modifier mechanism of organisms by gas chromatography confirmed that the citric acid in the graphite furnace in the pyrolysis product is mainly methane, hydrogen, carbon monoxide. Observed with the naked eye can be left on the walls of the new carbon. Graphite furnace in the atmosphere can affect the number of elements in the mechanism of atom formation. Pyrolysis of organic reagents have a strong reducing atmosphere, will speed up the reduction reaction oxide, resulting in some volatile elements in atomic temperature decline. Application of self-assembly of the temperature, measured before and after adding organic reagents of zinc, lead and secret of the atomic temperature T. , P, and thus that of graphite furnace atomic two graduate students to generate the response of the type of abstract. The results showed that after adding citric acid, zinc, lead, and the Yu T., p value, respectively, from n40K. IO50K and 119oK down to 670K, 870K and 83oK. Calculated by the three elements of the r Tapp are correspondingly reduced. Close to reduced heat of reaction in the atom H: (M). It can be speculated in the graphite furnace after adding citric acid,: zinc and other metal atoms close to the mechanism of generation of reduced oxides. General chemical equilibrium calculations and set-bed reactor simulation program preliminary study Xu Yuanyuan (Institute of Chemical Metallurgy, Chinese Academy of Sciences) 1.1 General calculation of chemical equilibrium and thermo-chemical database link, the progress of the adjustment method using a multi-system multi-phase chemical equilibrium calculation program. In this paper, an independent element in the selection algorithm proposed improvements can reduce the computational complexity. In addition, the function of the expansion of the program, so that the procedures in the importation of the following three conditions can be calculated, including: (1) to the set of atomic matrix elements of the standard Gibbs free energy generation and the initial molar; ( 2) given a set of independent measurement of chemical reaction coefficient matrix, equilibrium constants and the elements of the initial molar; (3) to the set of atomic matrix elements of the standard Gibbs free energy and the system generates the elements of group into. This article also on how this algorithm is used to dilute solution in the ion balance calculation to participate in the chemical analysis and derived the formula for calculating the corresponding. Of seven different types of system is calculated, the results show that: This procedure can be used for simultaneous chemical and phase equilibrium between the value calculated; even in response to a phase or some components tend to disappear, there is no difficulty computing ; computing speed faster than the general equilibrium but includes non-ideal system, the calculation results are not entirely satisfactory fashion. 1.2-bed reactor to save simulation process gas in accordance with the preliminary study of the whole series for a number of mixed reactor, solid-phase plug flow assumption for the establishment of a set-bed reactor of the simulation program, spreadsheet results with published literature basically in line with the measured data. Lead is an accumulation of harmful elements, widely distributed in nature. The source of lead in foods, including animal and vegetable materials, food additives and food contact of the pipe, container packaging materials, equipment and paint, etc., the transfer will lead to food 1. Lead long-term consumption of food containing harmful to the human body can cause chronic lead poisoning, also caused severe anemia in the absence of hemoglobin, vascular spasm, hypertension and other diseases. Therefore, food in particular is indispensable to daily life in the lead content of soy sauce seasoning test is especially important. China National Accreditation Board for Conformity Assessment of heavy metals detected sauce had laboratory proficiency testing as an important element. At present, the laboratory of lead in soy sauce Method for Determination of GB / T 5009.12-2003 the determination of lead in food, 2 The first method of graphite furnace atomic absorption spectrometry. I used to digest samples wet digestion, graphite furnace atomic absorption spectrometry to determine that the test should be paid attention to the following questions: Reagent blank Reagent blank with the reagents used in sample purity and cleanliness of the containers. In addition, the lead is widely distributed in nature. Therefore, it is easy to detect lead contamination, with low limits of trace analysis, the lower gap, the higher the accuracy. Therefore, gaps in the entire experiment to be very low, the experiment is necessary to strictly control. 2.1 Experimental water should be in line with GB / T 6682-2008 Laboratory analysis of water requirements and test methods 3 the requirements of the secondary water. 2.2 Experimental reagents superior level should be used pure, if there is no requirement in line with the purity of reagents, to be used in chemical purification method, but in the purification process, the solvent should be taken to avoid the possibility of secondary contamination, while the experimental selection of reagents, but also elements of a non-staining test for the baseline (in the experiment, if the sensitivity in the range of equipment under test can not detect the absorption signal elements can be selected that do not staining reagent test elements). 2.3 Experimental apparatus used to use acid water glass, and other equipment should be clean as possible. Emergency equipment such as glass, can be 10% 20% nitric acid boil 1 hour, and then冲净tap water and then deionized water冲净. It should be noted that the nitric acid solution immersion equipment can not be repeated long-term use, because of the long-term solution to use so that an increase in impurities such as lead, but pollution. Sample pre-treatment Using graphite furnace atomic absorption spectrometry determination of lead in soy sauce, the need for sample pre-treatment, that is to digest samples. A lot of sample digestion methods, I used wet digestion method, in the wet digestion of samples of soy sauce, it is necessary to note the following: 3.1 the use of reagents such as nitric acid, perchloric acid are corrosive, dangerous, and in the course of the experiment will produce a large number of acid fog and smoke. Therefore, the digestion should be carried out in the ventilation cabinet. 3.2 digestion process should be heated slowly at low temperature to prevent overheating, resulting in an instant a large amount of foam-like liquid spill and affect the accuracy of the results; digestion fluid changed as soon as brownish-black, should be cooled by adding nitric acid digestion continued until the digestive juice clarification until transparent or slightly yellow. 3.3 Of particular note is that the use of perchloric acid digestion of samples should be strict compliance with the rules, and to ensure that when the temperature reaches 200 degrees, only the existence of a small amount of organic ingredients. Otherwise, the oxidation potential of perchlorate at this temperature will rise rapidly and could lead to violent explosions. Therefore, the proposed resolution by adding nitric acid and perchloric acid mixture soak overnight, so that samples part of the organic component of the first oxidation, or to join the nitric acid, easily oxidized material damage, and then adding nitric acid or perchloric acid. 3.4 Digestion fluid can not be dry in order to prevent the loss of the elements measured. 3.5 as a result of too much acidity method of graphite furnace elements of a great impact, especially for the graphite tube of the damage is very great. Therefore, the digestion solution can not be too high concentration of acid. Transparent in the digestive juice clarification, the general need to increase water-soluble acid salts also in time. Acid rush to control temperature, to prevent the temperature is too high, leading to liquid splash, resulting in the loss of elements, so that the low results. Sample matrix modifier when the rational use of Fluid volume after digestion with atomic absorption spectrophotometer to measure, attention should be paid to the determination: 4.1 adjustment to the best state apparatus, in particular, sampling depth and about the appropriate location. Sample must be accurate and stable, it determines the standard curve linearity and reproducibility of the experiment. 4.2 According to the sensitivity of equipment and soy sauce samples of lead content of elements reasonable choice a