Name: preparing complex samples for analysis
Uploaded: 2024-12-05T18:31:55.000Z
Duration: 1 min 8 s
Channel: JoVE

Методы подготовки образцов для неорганического анализа зависят от свойств материала.
Многие неорганические вещества, нерастворимые в воде, могут быть солюбилизированы с помощью сильных минеральных кислот. Если они еще не растворены, используется более интенсивный метод, известный как техника плавления.
Здесь образец взвешивается и смешивается с флюсовым материалом в соотношении примерно 1 к 10 или 20. Смесь образца и флюса нагревается в платиновом тигле для получения расплавленной смеси. При охлаждении он затвердевает с образованием нового материала, растворимого в воде или разбавленной кислоте.
В отличие от них, органические материалы разлагаются методами сухого озоления и влажного сбраживания. При сухом озолении образец нагревают в муфельной печи с кислородом воздуха. В этом случае при сгорании органического материала образуется неорганический остаток для дальнейшего анализа.
При влажном сбраживании используется смесь кислот для расщепления органического материала.

Подготовка образцов для анализа: передовые методы

Точный анализ сложных образцов часто требует передовых методов подготовки для достижения надежных и воспроизводимых результатов. Образцы, содержащие неорганические или органические материалы, могут быть трудно растворимыми или разлагаемыми. Стандартные методы подготовки образцов включают кислотное разложение, сплавление, сухое озоление и мокрое разложение.

Кислотное разложение сильными кислотами обычно используется для растворения неорганических материалов, которые нерастворимы в воде. Этот метод может быть полезен для анализа образцов почвы или минералов. Во время кислотного разложения нерастворимый твердый образец тщательно измельчается или дробится для увеличения площади его поверхности, что обеспечивает более эффективную реакцию с кислотами. Обычно используемые кислоты включают соляную кислоту, азотную кислоту, серную кислоту и царскую водку — смесь азотной и соляной кислот. Каждая кислота обладает специфическими преимуществами для разных типов образцов:

<ul style="list-style-type: disc; display: flex; flex-direction: column; gap: 10px; padding: 0 0 0 40px;">
 <li>Соляная кислота (HCl) часто используется для растворения хлоридов, оксидов и карбонатов, а также эффективна для таких материалов, как металлы и руды.
 </li>
 <li>Азотная кислота (HNO_3) отлично подходит для расщепления органических веществ и окисления металлов, что делает ее обычным выбором для анализа биологических тканей или металлов.
 </li>
 <li>Серная кислота (H_2SO_4) используется, когда требуется сильный дегидратирующий агент, например, для растворения более устойчивых образцов, таких как сульфиды или металлы.
 </li>
 <li>Царская водка, смесь азотной и соляной кислот, особенно эффективна для растворения благородных металлов, таких как золото и платина, которые устойчивы к воздействию отдельных кислот.
 </li>
</ul>
Образец обрабатывается выбранной высококонцентрированной кислотой в подходящем контейнере, где он разлагается на растворимые формы или ионы. Для ускорения процесса разложения можно также применять тепло. После разложения полученная смесь, разбавленная водой, пригодна для дальнейшего анализа.

Метод слияния является альтернативным методом растворения неорганических материалов, которые не могут быть разложены до растворимой формы путем кислотного разложения. Здесь взвешенный образец смешивается с флюсом в определенном соотношении, обычно около 1:10 или 1:20. Смесь образца и флюса помещается в платиновый тигель, устойчивый к высоким температурам и химическим реакциям. Этот тигель нагревается в высокотемпературной печи для получения расплавленной смеси. После нагрева расплавленную смесь оставляют остывать до тех пор, пока она не даст новый материал, растворимый в воде или разбавленной кислоте.

Несколько примеров использования флюсов при подготовке образцов для растворения твердых и жидких соединений:

<ul style="list-style-type: disc; display: flex; flex-direction: column; gap: 10px; padding: 0 0 0 40px;">
 <li>Na_2CO_3 и Na_2O_2 в качестве флюсов для сплавов железа и хрома: карбонат натрия (Na_2CO_3) является широко используемым флюсом, но в некоторых случаях используется перекись натрия (Na_2O_2) из-за ее более сильных окислительных свойств. Эта комбинация особенно полезна для растворения сплавов железа и хрома в никелевом тигле. 
 </li>
 <li>Смесь Li_2B_4O_7 и Li_2SO_4 для быстрого растворения: смесь тетрабората лития (Li_2B_4O_7) и сульфата лития (Li_2SO_4) в соотношении 2:1 по массе выделяется своей быстрой способностью растворять тугоплавкие силикаты и оксиды.
 </li>
</ul>
Методы сухого озоления и мокрого разложения широко используются для разложения органических материалов. При сухом озолении органический образец нагревается в муфельной печи при высокой температуре. Тепло вызывает сгорание органического материала в присутствии атмосферного кислорода, оставляя неорганический остаток, или «пепел». Этот пепел затем можно растворить в соответствующем растворителе для дальнейшего анализа. Мокрое разложение подразумевает использование кислот для расщепления органического материала.

Точный анализ сложных образцов часто требует передовых методов подготовки для получения надежных и воспроизводимых результатов. Образцы, содержащие ...

sample-preparation-for-analysis-advanced-techniques

Education

JoVE Core

Analytical Chemistry

Аналитическая химия

Unit 1

Раздел 1

Method Development and Sampling Techniques

Разработка методов и техники отбора проб

method-development-and-sampling-techniques

KEY TERMS AND CONCEPTS

ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

Sample Preparation for Analysis: Advanced Techniques

preparing complex samples for analysis

Preparing complex samples for analysis often requires special digestion and fusion methods. Samples with inorganic or organic material can be hard to dissolve or break down. Common sample preparation methods include acid digestion, fusion, dry ashing, and wet digestion. These steps help turn difficult samples into forms that can be tested reliably and again with similar results.

Acid digestion is often used for inorganic materials that do not dissolve in water. It is useful for soil and mineral samples. The solid sample is first finely ground or crushed to increase surface area, which helps it react better with the acid. Common acids include hydrochloric acid, nitric acid, sulfuric acid, and aqua regia, which is a mixture of nitric and hydrochloric acids.

Each acid has a different use. Hydrochloric acid, or HCl, is often used for chlorides, oxides, and carbonates, and it also works on metals and ores. Nitric acid, or HNO3, is good for breaking down organic matter and oxidizing metals, so it is often used for biological tissues or metal analysis. Sulfuric acid, or H2SO4, is useful when a strong dehydrating agent is needed, such as for more resistant sulfides or metals. Aqua regia is especially effective for noble metals like gold and platinum, which resist individual acids.

During digestion, the sample is placed in a suitable container and treated with the chosen strong acid. Heat may be added to speed up the process. The sample changes into soluble forms or ions, and the final mixture is diluted with water before further analysis. Fusion is another way to dissolve inorganic materials when acid digestion is not enough. In this method, the weighed sample is mixed with a flux in a ratio of about 1 to 10 or 20, then heated in a platinum crucible in a high-temperature furnace until it melts.

After cooling, the fused material becomes soluble in water or dilute acid. Some flux examples are sodium carbonate and sodium peroxide for iron and chromium alloys in a nickel crucible. Potassium disulfate, K2S2O7, works well for refractory oxides and can be made by heating potassium hydrogen sulfate to remove foaming byproducts. A mixture of lithium tetraborate and lithium sulfate in a 2:1 ratio is also used because it dissolves refractory silicates and oxides quickly.

Organic samples are often prepared by dry ashing or wet digestion. In dry ashing, the sample is heated in a muffle furnace at high temperature. The organic material burns in air and leaves behind an inorganic residue called ash. That ash can then be dissolved in a suitable solvent for analysis. Wet digestion also breaks down organic material, but it does so with acids.

Preparing Complex Samples for Analysis

development of analytical methods

Analytical Methods: Technique to Protocol

Analytical methods follow a clear path from technique to protocol. In analytical chemistry, a technique is the scientific principle used to explain a chemical measurement. A method applies that technique to a sample of interest. The next steps are procedure and protocol. A procedure gives the directions for carrying out the analysis with an analytical method. A protocol is the detailed set of guidelines for that procedure, and it should be followed closely to get the desired results. <br...

quality control

Quality Control Charts and Lab Records

Quality control charts, proficiency testing, and lab records are key parts of quality control in a laboratory. These steps help keep a system under statistical control. They also help track data, show trends, and spot variations that may affect the accuracy of an analysis. One common tool is a quality control chart. This chart plots one or more analytical characteristics over time. The measured values are taken at different times during the analysis and compared with the known value of...

quality assurance

Quality Checks in Analytical Testing

Quality assurance in analytical testing brings together the checks that help a system perform properly. It includes quality control, quality assessment, and internal corrective measures. These parts work in a cycle to support reliable results. Quality control happens before and during the analysis. Quality assessment takes place during and after the investigation. Internal corrective measures are then based on the results of post-analysis quality assessment, or they may be applied before a new...

data validation

How Analytical Methods Are Checked

Method validation checks whether an analytical chemistry method gives reliable results. It is especially important when the same method is used with different sample matrices or when the procedure is changed. Validation helps show that the method still meets acceptable standards in each case. Several key checks are used in method validation. Specificity means the method can measure the target analyte without interference from other substances. Linearity means the result changes in direct...

qualitative analysis

Classical and Instrumental Sample ID

Qualitative analysis identifies the elements, ions, or compounds in an unknown sample. It is the first step in the hierarchy of analytical goals. That makes it the starting point for scientific study before quantitative analysis or other forms of analysis. Two main approaches are used in qualitative analysis: classical methods and instrumental methods. Classical methods depend on the visible or sensory result of a chemical reaction, such as a color change, a precipitate, or even a smell. These...

quantitative analysis

Measuring Analyte Concentration

Quantitative analysis measures the amount of a specific substance, called the analyte, in a sample. If the sample composition is unknown, qualitative analysis comes first. That step identifies the components so the correct substances can be measured during the quantitative phase. This method depends on two key measurements. Scientists measure the sample quantity and also a property that is proportional to the amount of analyte. Together, these measurements help determine the analyte...

instrument calibration

Calibrating Lab Instruments for Accurate Results

Calibration helps lab instruments produce accurate and consistent results. It is important in manufacturing, healthcare, testing laboratories, and scientific research. Each instrument needs a calibration process that matches its design and function. This process improves data accuracy and helps results stay reliable. An analytical balance measures mass and needs regular calibration to stay precise. It is calibrated by comparing its readings with known standard weights. These weights act as...

glassware calibration

Calibrating Lab Glassware for Accurate Volume

Calibrating lab glassware helps students measure liquids accurately in the analytical laboratory. It reduces volume errors and supports consistent results across measurements. This matters when using volumetric flasks, pipettes, burettes, and other tools that depend on precise volume readings. Volumetric flasks are used to prepare aqueous solutions with a precise final volume. They have a calibration line on the neck. To calibrate one, fill it with distilled water until the meniscus, the...

standard solutions

Preparing Standard Solutions in the Lab

Standard solutions are prepared to have a precisely known concentration or composition. In analytical chemistry, this accuracy is important because it supports reliable results. A primary standard is a highly pure, stable substance with a high molar mass. It is fully soluble in water, which is the most commonly used solvent in analytical chemistry. A primary standard solution can be used to standardize a secondary standard. Secondary standards have known concentrations, but they are usually...

blank solutions

Blank Solutions in Analytical Testing

Blank solutions are used in analytical testing to show the background signal before a sample is measured. A blank solution does not contain the analyte, which is the substance of interest being tested or measured. It is usually made with the same reagents and procedure as the sample solution, but without the analyte. The main purpose of a blank solution is to control for background interference and contamination. Reagents, solvents, or lab equipment can sometimes create a detectable signal on...

sampling methods: overview

How Sampling Shapes Lab Results

Sampling shapes lab results by determining how a smaller sample represents a larger population. In analytical chemistry, testing an entire population is often impractical or impossible, so samples are collected to make inferences about the whole group. The sampling method is the process used to choose individuals or items for that sample. Common sampling methods include random, judgemental, systematic, stratified, and cluster sampling. Each method can affect the quality of the data in a...

sampling methods: sample types

Sampling Materials in Solid, Liquid, Gas

Sampling materials are grouped as solid, liquid, or gas. The type of sample helps decide the right collection method. Solid samples can include sediments from water bodies, soil, metals, and biological tissues. Sediment sampling from water bodies can be done in two common ways. Grab sampling uses a device to collect a discrete sample from the bottom with minimal disturbance. These samples may not show the full area because conditions can vary from place to place. Piston coring collects a...

sampling plans

Choosing Samples for Reliable Results

Sampling is a key step in analytical chemistry. It helps researchers collect data that represents a larger population. The main sampling methods in this topic are random, judgmental, systematic, stratified, and cluster sampling. Random sampling gives each member of the population an equal chance of being chosen. Researchers often use a random number generator or a lottery-style method. For example, a polymer sheet can be divided into 1 cm x 1 cm sections, and 10 sections can be selected at...

sample preparation for analysis: overview

Preparing Samples by State and Form

Sample preparation depends on the state and form of the sample before analysis. It helps make the sample ready for accurate measurement. The main goal is to extract the analyte, which is the substance being measured, and remove parts that could interfere with the analysis. Solid samples often need the most handling. Large solids are usually ground, crushed, or milled to make them smaller and increase surface area. The sample is then sieved and mixed so it has a uniform composition. After that,...

sample preparation for analysis: advanced techniques

Preparing complex samples for analysis often requires special digestion and fusion methods. Samples with inorganic or organic material can be hard to dissolve or break down. Common sample preparation methods include acid digestion, fusion, dry ashing, and wet digestion. These steps help turn difficult samples into forms that can be tested reliably and again with similar results. Acid digestion is often used for inorganic materials that do not dissolve in water. It is useful for soil and...

sample handling

Sample Transport and Storage Basics

Sample transport and storage help keep specimens intact before testing. Moving a sample from the collection point to the laboratory requires careful handling. The sample should be sealed well and clearly labeled. These steps help prevent cross-contamination and support reliable results. Temperature control is also important during transport. Some samples travel in insulated containers, cool packs, or refrigerated vehicles so they stay within the needed temperature range. After the samples...

contaminants and errors

Sampling Errors in Sample Preparation

Sampling errors in sample preparation can affect the accuracy of laboratory results. Two common problems are concentration bias from poor sample splitting and contamination from reducing particle size by grinding or homogenization. Recognizing these errors helps make analysis more reliable. The number of samples also matters when a target population follows a normal distribution. In that case, the sample size ns can be found with a formula that uses the t-value for the chosen confidence level,...

key terms and concepts

Learn how acid digestion, fusion, dry ashing, and wet digestion prepare complex samples for analysis, including soil, minerals, metals, and organic tissue.

Preparing Complex Samples for Analysis | JoVE K12

analytical chemistry

JoVE Core Analytical Chemistry simplifies complex chemical principles by breaking them down into clear, engaging animations, making topics from SI Units to NMR spectroscopy more accessible and straightforward. Additionally, the scientist-in-action videos highlight the application of these concepts in real-world research conducted in laboratories globally.

Preparing Complex Samples for Analysis

Description

Transcript

Tags