1.1 本规程涵盖了在原子光谱法测定元素之前使用微波辐射进行样品分解的程序。 1.1.1 虽然本规程基于电感耦合等离子体原子发射光谱法（ICP-AES）和原子吸收光谱法（AAS）作为主要测量技术的使用，但如果需要较低的检测限并达到分析性能标准，则可以使用其他原子光谱法技术。 1.2 本规程适用于石油产品和润滑剂，如润滑脂、添加剂、润滑油、汽油和柴油。 1.3 虽然不属于D02委员会的管辖范围，但该做法也适用于其他化石燃料产品，如煤、飞灰、煤灰、焦炭和油页岩。 1.3.1 中给出了一些实际使用微波加热进行化石燃料产品和其他材料元素分析的示例 表1 . （A） 括号中的黑体数字指本标准末尾的参考文献列表。 1.3.2 非化石燃料领域微波辅助分析的ASTM方法的其他一些示例包括在 附录X1 . 1.4 在样品溶解过程中，样品可能会被各种酸混合物分解。为所有类型样品中存在的所有可能元素组合指定适当的酸混合物超出了本规程的范围。但是，如果溶解导致任何可见的不溶性物质，假设不溶性物质包含一些感兴趣的分析物，则本规程可能不适用于所分析的样品类型。 1.5 这种微波辅助分解过程可能导致样品中砷、硼、铬、汞、锑、硒和/或锡等“挥发性”元素的损失。在这种溶解中，元素的化学种类也是一个问题，因为某些种类可能无法消化，并且具有不同的样品引入效率。 1.6 应使用参考材料或合适的NIST标准参考材料来确认分析物的回收。如果这些不可用，则应在微波消解之前用已知浓度的分析物添加样品。 1.7 有关石油产品和润滑剂元素分析的样品制备程序的更多信息，请参见实践 D7455 . 1.8 以国际单位制表示的数值应视为标准值。本标准不包括其他计量单位。 1.9 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全、健康和环境实践，并确定监管限制的适用性。 第节给出了具体的警告声明 6. 和 7. . 1.10 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《关于制定国际标准、指南和建议的原则的决定》中确立的国际公认标准化原则制定的。 ====意义和用途====== 5.1 通常，在原子光谱测量之前，有必要溶解样品，尤其是固体样品。使用微波炉溶解此类样品是有利的，因为它是一种更快速的溶解样品的方法，而不是使用压力分解容器或其他方法在酸性溶液中溶解样品的传统程序。 5.2 微波溶解的优点包括由于密封容器内的高温和高压而更快地消化。使用密闭容器还可以消除样品中存在的或样品溶解过程中形成的挥发性物质的不受控制的微量元素损失。 挥发性元素砷、硼、铬、汞、锑、硒和锡可能会通过一些开放容器酸溶解程序损失。与开放容器程序相比，微波辅助溶解的另一个优点是可以更好地控制空白中的潜在污染。这是因为实验室环境的污染较少，容器不干净，使用的试剂数量较少 ( 9 ) . 5.3 由于令人满意的设备的不同品牌和型号之间存在差异，因此无法提供详细的操作说明。相反，分析员应该遵循特定设备制造商提供的说明。 5.4 微波加热机理- 微波加热一种材料的速度比另一种材料快得多，因为材料吸收微波的能力因其极性而异。 微波炉是一种高能量源，可以快速加热样品。然而，仍然需要进行化学反应，以将样品完全溶解到酸性混合物中。与仅外部加热的传统加热不同，微波加热是内部和外部的。样品颗粒与酸之间更好的接触是快速溶解的关键。因此，重的无孔材料，如燃油或焦炭，不能通过微波加热有效溶解。单个颗粒上发生的局部内部加热可能导致颗粒破裂，从而使新鲜表面暴露于试剂接触。与介电粒子接触的加热的介电液体（水/酸）在粒子表面上方产生几个数量级的热量。 这会产生较大的热对流，从而搅动和清除溶解溶液的停滞表面层，从而使新鲜表面暴露在新鲜溶液中。然而，单纯的微波加热不会破坏化学键，因为质子能量低于化学键的强度 ( 5. ) . 5.4.1 在电磁辐射区，酸性溶液和电磁辐射的结合导致碳质固体中的无机成分几乎完全溶解。显然，电磁能促进酸与无机成分的反应，从而促进这些成分的溶解，而不会破坏任何含碳材料。 据信，电磁辐射是一种高能量源，可快速加热酸溶液以及浆液中单个颗粒的内部和外部。这种快速而强烈的内部加热要么促进无机成分在溶液中的扩散过程，要么使单个颗粒破裂，从而使更多的无机成分暴露于活性酸中。含水液体本身产生的热量将在液-固界面周围的不同点发生变化，这可能会产生较大的热对流，该对流可以搅动并将含溶解无机成分的废酸溶液从含碳颗粒的表层扫走，从而使颗粒表面暴露于新鲜酸中 ( 16 ) . 5.4.2 与其他加热机制不同，微波加热的真正控制是可能的，因为停止能量的应用会立即停止加热（当纯化合物被消化时，放热可能很快）。热流方向与传统加热相反，因为微波能量被容器中的物质吸收，能量被转换为热量，物质的整体温度升高。热量从试剂和样品混合物转移到容器中，并通过传导到周围大气而散失。由轻质而坚固的聚合物制成的新型合成容器可以承受超过240 °C温度和800以上 psi压力。 在含有有机化合物的样品的消化过程中，大部分不溶性气体，如CO 2. 已形成。这些气体在任何温度下与试剂的蒸汽压结合，形成容器内的总压力。由于微波消解容器的热流与电阻装置的热流相反，因此在相同温度下，微波溶解产生的总压力显著低于其他类似加热装置或系统。这意味着，与通常预期的压力容器相比，更大的样品可以在更高的温度和更低的压力下消化。应控制样本量，以防止因过量CO而加剧的快速放热破裂 2. 一代然而，由于试剂产生的蒸汽压，容器的压力限制仍然限制了可使用的样品尺寸和可达到的最高温度 ( 17 ) . 5.4.3 有机和聚合物样品可能特别有问题，因为它们极易挥发，并产生大量气体副产物，如CO 2. 而且没有 x . 因此，较大的样品尺寸将在消解容器内产生更高的压力。一般不超过1 g这些样品类型可以在密闭容器中消化 ( 18 ) . 5.4.3.1 在开放式消化容器系统中，操作温度受酸溶液沸点的限制，温度为200℃ °C至260 °C范围通常可以在密封的消化容器中实现。 这导致反应动力学的急剧加速，使消化反应能够在较短的时间内进行。然而，较高的温度会导致容器内的压力升高，从而产生潜在的安全隐患。快速加热样品溶液可在消化过程中引发放热反应。因此，在现代微波消解系统中，引入了用于温度和压力控制的传感器和联锁装置。由于不同类型的样品在微波场中表现不同，因此在该操作中需要加热控制 ( 19 ) . 5.4.4 微波加热是因为微波反应器产生的电磁场与材料中的极化分子或离子相互作用。 当极化物种竞争使其偶极子与振荡场对齐时，它们旋转、迁移并相互摩擦，导致它们加热。这种微波效应不同于使用热板通过传导实现的间接加热 ( 20 ) .

1.1 This practice covers the procedure for use of microwave radiation for sample decomposition prior to elemental determination by atomic spectroscopy. 1.1.1 Although this practice is based on the use of inductively coupled plasma atomic emission spectrometry (ICP-AES) and atomic absorption spectrometry (AAS) as the primary measurement techniques, other atomic spectrometric techniques may be used if lower detection limits are required and the analytical performance criteria are achieved. 1.2 This practice is applicable to both petroleum products and lubricants such as greases, additives, lubricating oils, gasolines, and diesels. 1.3 Although not a part of Committee D02’s jurisdiction, this practice is also applicable to other fossil fuel products such as coal, fly ash, coal ash, coke, and oil shale. 1.3.1 Some examples of actual use of microwave heating for elemental analysis of fossil fuel products and other materials are given in Table 1 . (A) The boldface numbers in parentheses refer to the list of references at the end of this standard. 1.3.2 Some additional examples of ASTM methods for microwave assisted analysis in the non-fossil fuels area are included in Appendix X1 . 1.4 During the sample dissolution, the samples may be decomposed with a variety of acid mixture(s). It is beyond the scope of this practice to specify appropriate acid mixtures for all possible combinations of elements present in all types of samples. But if the dissolution results in any visible insoluble material, this practice may not be applicable for the type of sample being analyzed, assuming the insoluble material contains some of the analytes of interest. 1.5 It is possible that this microwave-assisted decomposition procedure may lead to a loss of “volatile” elements such as arsenic, boron, chromium, mercury, antimony, selenium, and/or tin from the samples. Chemical species of the elements is also a concern in such dissolutions since some species may not be digested and have a different sample introduction efficiency. 1.6 A reference material or suitable NIST Standard Reference Material should be used to confirm the recovery of analytes. If these are not available, the sample should be spiked with a known concentration of analyte prior to microwave digestion. 1.7 Additional information on sample preparation procedures for elemental analysis of petroleum products and lubricants can be found in Practice D7455 . 1.8 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific warning statements are given in Sections 6 and 7 . 1.10 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 Often it is necessary to dissolve the sample, particularly if it is a solid, before atomic spectroscopic measurements. It is advantageous to use a microwave oven for dissolution of such samples since it is a far more rapid way of dissolving the samples instead of using the traditional procedures of dissolving the samples in acid solutions using a pressure decomposition vessel, or other means. 5.2 The advantage of microwave dissolution includes faster digestion that results from the high temperature and pressure attained inside the sealed containers. The use of closed vessels also makes it possible to eliminate uncontrolled trace element losses of volatile species that are present in a sample or that are formed during sample dissolution. Volatile elements arsenic, boron, chromium, mercury, antimony, selenium, and tin may be lost with some open vessel acid dissolution procedures. Another advantage of microwave aided dissolution is to have better control of potential contamination in blank as compared to open vessel procedures. This is due to less contamination from laboratory environment, unclean containers, and smaller quantity of reagents used ( 9 ) . 5.3 Because of the differences among various makes and models of satisfactory devices, no detailed operating instructions can be provided. Instead, the analyst should follow the instructions provided by the manufacturer of the particular device. 5.4 Mechanism of Microwave Heating— Microwaves have the capability to heat one material much more rapidly than another since materials vary greatly in their ability to absorb microwaves depending upon their polarities. Microwave oven is acting as a source of intense energy to rapidly heat the sample. However, a chemical reaction is still necessary to complete the dissolution of the sample into acid mixtures. Microwave heating is internal as well as external as opposed to the conventional heating which is only external. Better contact between the sample particles and the acids is the key to rapid dissolution. Thus, heavy nonporous materials such as fuel oils or coke are not as efficiently dissolved by microwave heating. Local internal heating taking place on individual particles can result in the rupture of the particles, thus exposing a fresh surface to the reagent contact. Heated dielectric liquids (water/acid) in contact with the dielectric particles generate heat orders of magnitude above the surface of a particle. This can create large thermal convection currents which can agitate and sweep away the stagnant surface layers of dissolved solution and thus, expose fresh surface to fresh solution. Simple microwave heating alone, however, will not break the chemical bonds, since the proton energy is less than the strength of the chemical bond ( 5 ) . 5.4.1 In the electromagnetic irradiation zone, the combination of the acid solution and the electromagnetic radiation results in near complete dissolution of the inorganic constituents in the carbonaceous solids. Evidently, the electromagnetic energy promotes the reaction of the acid with the inorganic constituents thereby facilitating the dissolution of these constituents without destroying any of the carbonaceous material. It is believed that the electromagnetic radiation serves as a source of intense energy which rapidly heats the acid solution and the internal as well as the external portions of the individual particles in the slurry. This rapid and intense internal heating either facilitates the diffusion processes of the inorganic constituents in solution or ruptures the individual particles thereby exposing additional inorganic constituents to the reactive acid. The heat generated in the aqueous liquid itself will vary at different points around the liquid-solid interface and this may create large thermal convection currents which can agitate and sweep away the spent acid solution containing dissolved inorganic constituents from the surface layers of the carbonaceous particles thus exposing the particle surfaces to fresh acid ( 16 ) . 5.4.2 Unlike other heating mechanisms, true control of microwave heating is possible because stopping of the application of energy instantly halts the heating (except the exotherms which can be rapid when pure compounds are digested). The direction of heat flow is reversed from conventional heating, as microwave energy is absorbed by the contents of the container, energy is converted to heat, and the bulk temperature of the contents rises. Heat is transferred from the reagent and sample mixture to the container and dissipated through conduction to the surrounding atmosphere. Newer synthesized containers made up of light yet strong polymers can withstand over 240 °C temperatures and over 800 psi pressure. During the digestion process of samples containing organic compounds, largely insoluble gases such as CO 2 are formed. These gases combine with the vapor pressure from the reagents, at any temperature, to produce the total pressure inside the vessel. Since the heat flow from a microwave digestion vessel is reversed from that of resistive devices, the total pressures generated for microwave dissolutions are significantly lower at the same temperature than other comparably heated devices or systems. This means larger samples can be digested at higher temperatures and lower pressures than would normally be expected from such pressurized vessels. Sample size should be controlled to prevent rapid exotherm rupture, exacerbated by excess CO 2 generation. However, the pressure limitations of the vessel still restrict both the sample size that can be used and the maximum temperature that can be achieved due to the vapor pressure resulting from the reagents ( 17 ) . 5.4.3 Organic and polymer samples can be especially problematic because they are highly volatile and produce large amounts of gaseous by-products such as CO 2 and NO x . As a result larger sample sizes will produce higher pressures inside the digestion vessel. Generally, no more than 1 g of these sample types can be digested in a closed vessel ( 18 ) . 5.4.3.1 While in open digestion vessel systems the operating temperatures are limited by the acid solutions’ boiling points, temperatures in the 200 °C to 260 °C range can be typically achieved in sealed digestion vessels. This results in a dramatic acceleration of the reaction kinetics, allowing the digestion reactions to be carried out in a shorter time period. The higher temperatures, however, result in a pressure increase in the vessel and thus in a potential safety hazard. Rapid heating of the sample solution can induce exothermic reactions during the digestion process. Therefore in modern microwave digestion systems, sensors and interlocks for temperature and pressure control are introduced. Since different types of sample behave differently in microwave field, heating control is necessary in this operation ( 19 ) . 5.4.4 Microwave heating occurs because microwave reactors generate an electromagnetic field that interacts with polarizable molecules or ions in the materials. As the polarized species compete to align their dipoles with the oscillating field, they rotate, migrate, and rub against each other, causing them to heat up. This microwave effect differs from indirect heating by conduction achieved by using a hot plate ( 20 ) .