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

Les méthodes de préparation des échantillons pour l'analyse inorganique dépendent des propriétés du matériau.
De nombreuses matières inorganiques insolubles dans l’eau peuvent être solubilisées à l’aide d’acides minéraux forts. S’ils ne sont pas encore dissous, une méthode plus intensive, connue sous le nom de technique de fusion, est utilisée.
Ici, l’échantillon est pesé et mélangé à un matériau fondant dans un rapport d’environ 1 à 10 ou 20. Le mélange échantillon-flux est chauffé dans un creuset en platine pour obtenir un mélange fondu. En refroidissant, celui-ci se solidifie pour donner un nouveau matériau soluble dans l’eau ou l’acide dilué.
En revanche, les matières organiques sont décomposées par des méthodes d’incinération sèche et de digestion humide. Dans le cas de la cuisson à sec, l’échantillon est chauffé dans un four à moufle avec de l’oxygène atmosphérique. Ici, la combustion de la matière organique génère un résidu inorganique pour une analyse plus approfondie.
La digestion humide utilise un mélange d’acides pour décomposer la matière organique.

préparation d'échantillons pour analyse : techniques avancées

L’analyse précise d’échantillons complexes nécessite souvent des techniques de préparation avancées pour obtenir des résultats fiables et reproductibles. Les échantillons contenant des matières inorganiques ou organiques peuvent être difficiles à dissoudre ou à décomposer efficacement. Les méthodes standard de préparation d’échantillons comprennent la digestion acide, la fusion, la calcination à sec et la digestion humide.

La digestion acide avec des acides forts est couramment utilisée pour dissoudre les matières inorganiques insolubles (qui ne se dissolvent pas) dans l’eau. Cette méthode peut être utile pour analyser des échantillons de sol ou de minéraux. Pendant la digestion acide, l’échantillon solide insoluble est finement broyé ou concassé pour augmenter sa surface, ce qui permet une réaction plus efficace avec les acides. Les acides généralement utilisés comprennent l’acide chlorhydrique, l’acide nitrique, l’acide sulfurique et l’eau régale, un mélange d’acide nitrique et chlorhydrique. Chaque acide présente des avantages spécifiques pour différents types d’échantillons :

<ul style="list-style-type: disc; padding-left: 35px; margin: 0;">
	<li>L’acide chlorhydrique (HCl) est souvent utilisé pour dissoudre les chlorures, les oxydes et les carbonates et est également efficace sur des matériaux tels que les métaux et les minerais.</li>
	<li>L’acide nitrique (HNO_3) est excellent pour décomposer la matière organique et oxyder les métaux, ce qui en fait un choix courant pour les tissus biologiques ou l’analyse des métaux.</li>
	<li>L’acide sulfurique (H_2SO_4) est utilisé lorsqu’un agent déshydratant puissant est nécessaire, par exemple pour dissoudre des échantillons plus résistants comme les sulfures ou les métaux.</li>
	<li>L’eau régale, un mélange d’acides nitrique et chlorhydrique, est particulièrement efficace pour dissoudre les métaux nobles comme l’or et le platine, qui résistent aux acides individuels.</li>
</ul>

L’échantillon est traité avec l’acide à haute concentration choisi dans un récipient approprié, où il est décomposé en formes solubles ou en ions. De la chaleur peut également être appliquée pour accélérer le processus de digestion. Après digestion, le mélange obtenu dilué avec de l’eau peut être utilisé pour une analyse plus approfondie.

La technique de fusion est une méthode alternative pour dissoudre les matières inorganiques qui ne peuvent pas être décomposées en une forme soluble par digestion acide. Ici, l’échantillon pondéré est mélangé à un matériau de flux dans un rapport spécifique, généralement d’environ 1 à 10 ou 20. Le mélange échantillon-flux est placé dans un creuset en platine résistant aux températures élevées et aux réactions chimiques. Ce creuset est chauffé dans un four à haute température pour obtenir un mélange fondu. Après chauffage, le mélange fondu est laissé refroidir jusqu’à ce qu’il donne un nouveau matériau soluble dans l’eau ou l’acide dilué. 
Plusieurs exemples d’utilisation de flux dans la préparation d’échantillons pour dissoudre des composés solides et liquides sont les suivants :

<ul style="list-style-type: disc; padding-left: 35px; margin: 0;">
	<li>Na_2CO_3 et Na_2O_2 comme flux pour les alliages de fer et de chrome : Le carbonate de sodium (Na_2CO_3) est un flux couramment utilisé, mais le peroxyde de sodium (Na_2O_2) est utilisé en raison de sa plus forte capacité oxydante dans certains cas. Cette combinaison est particulièrement utile pour dissoudre les alliages de fer et de chrome dans un creuset en nickel.</li>
	<li>Mélange Li_2B_4O_7 et Li_2SO_4 pour une dissolution rapide : Un mélange de tétraborate de lithium (Li_2B_4O_7) et de sulfate de lithium (Li_2SO_4) dans un rapport de 2:1 en poids est mis en évidence pour sa capacité rapide à dissoudre les silicates et les oxydes réfractaires.</li>
</ul>

Les méthodes de calcination à sec et de digestion par voie humide sont couramment utilisées pour décomposer les matières organiques. Dans la calcination à sec, l’échantillon organique est chauffé dans un four à moufle à haute température. La chaleur provoque la combustion de la matière organique en présence d’oxygène atmosphérique, laissant derrière elle un résidu inorganique, ou « cendre ». Cette cendre peut ensuite être dissoute dans un solvant approprié pour une analyse plus approfondie. La digestion humide implique l’utilisation d’acides pour décomposer la matière organique.

Préparation d'échantillons pour analyse : techniques avancées

L’analyse précise d’échantillons complexes nécessite souvent des techniques de préparation avancées pour obtenir des résultats fiables et reproductibles. Échantillons contenant ...

sample-preparation-for-analysis-advanced-techniques

Education

Enseignement

JoVE Core

Analytical Chemistry

Chimie analytique

Unit 1

Unité 1

Method Development and Sampling Techniques

Développement de méthodes et techniques d'échantillonnage

method-development-and-sampling-techniques

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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