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

I metodi di preparazione dei campioni per l'analisi inorganica dipendono dalle proprietà del materiale.
Molti materiali inorganici insolubili in acqua possono essere solubilizzati utilizzando acidi minerali forti. Se non sono ancora disciolti, viene utilizzato un metodo più intensivo, noto come tecnica di fusione.
Qui, il campione viene pesato e miscelato con un materiale fondente in un rapporto di circa 1 a 10 o 20. La miscela campione-flusso viene riscaldata in un crogiolo di platino per ottenere una miscela fusa. Al raffreddamento, questo si solidifica per produrre un nuovo materiale solubile in acqua o acido diluito.
Al contrario, i materiali organici vengono decomposti mediante incenerimento a secco e metodi di digestione a umido. Nell'incenerimento a secco, il campione viene riscaldato in un forno a muffola con ossigeno atmosferico. Qui, la combustione del materiale organico genera un residuo inorganico per ulteriori analisi.
La digestione a umido utilizza una miscela di acidi per scomporre il materiale organico.

preparazione del campione per l'analisi: tecniche avanzate

Un'analisi accurata di campioni complessi richiede spesso delle tecniche di preparazione avanzate per ottenere dei risultati affidabili e riproducibili. I campioni contenenti materiali inorganici, o organici, possono essere difficili da sciogliere o decomporre in modo efficace. I metodi standard di preparazione del campione includono la digestione acida, la fusione, l’incenerimento a secco e la digestione a umido.

La digestione acida con gli acidi forti è comunemente usata per sciogliere materiali inorganici insolubili (che non si sciolgono) in acqua. Questo metodo può essere utile per analizzare campioni di terreno o minerali. Durante la digestione acida, il campione solido insolubile viene finemente macinato, o frantumato, per aumentarne l'area superficiale, il che consente una reazione più efficace con gli acidi. Gli acidi che vengono tipicamente usati includono l’acido cloridrico, l’acido nitrico, l’acido solforico e l’acqua regia, una miscela di acido nitrico e cloridrico. Ogni acido ha dei vantaggi specifici per i diversi tipi di campione:

<ul style="list-style-type: disc; display: flex; flex-direction: column;">
	<li>L'acido cloridrico (HCl) è spesso utilizzato per sciogliere i cloruri, gli ossidi e i carbonati ed è efficace anche su materiali come i metalli e i minerali.</li>
	<li>L'acido nitrico (HNO_3) è eccellente per la scomposizione della materia organica e per l'ossidazione dei metalli, il che lo rende una scelta comune per i tessuti biologici o l’analisi dei metalli.</li>
	<li>L'acido solforico (H_2SO_4) viene usato quando è necessario un forte agente disidratante, ad esempio per sciogliere i campioni più resistenti come i solfuri o i metalli.</li>
	<li>L'acqua regia, una miscela di acido nitrico e cloridrico, è particolarmente efficace per sciogliere dei metalli nobili come l’oro e il platino, che sono resistenti ai singoli acidi.</li>
</ul>

Il campione viene trattato con l'acido ad alta resistenza scelto in un contenitore adatto, dove viene scomposto in forme solubili o ioni. Si può anche applicare del calore per accelerare il processo di digestione. Dopo la digestione, la miscela risultante diluita con l’acqua è adatta per ulteriori analisi.

La tecnica di fusione è un metodo alternativo per sciogliere i materiali inorganici che non possono essere scomposti in una forma solubile tramite la digestione acida. In questo caso, il campione pesato viene miscelato con un materiale di flusso in un rapporto specifico, in genere circa 1 a 10 o 20. La miscela campione-flusso viene posta in un crogiolo di platino resistente alle alte temperature e alle reazioni chimiche. Questo crogiolo viene riscaldato in un forno ad alta temperatura per ottenere una miscela fusa. Dopo il riscaldamento, la miscela fusa viene lasciata raffreddare fino a quando non produce un nuovo materiale solubile in acqua o acido diluito.

Diversi esempi di utilizzo del flusso nella preparazione del campione per la dissoluzione di composti solidi e liquidi sono:

<ul style="list-style-type: disc; display: flex; flex-direction: column;">
	<li>Na_2CO_3 e Na_2O_2 come flussi per leghe di ferro e cromo: il carbonato di sodio (Na_2CO_3) è un flusso comunemente utilizzato, ma il perossido di sodio (Na_2O_2), in alcuni casi, viene impiegato per la sua maggiore capacità ossidante. Questa combinazione è particolarmente utile per la dissoluzione di leghe di ferro e cromo in un crogiolo di nichel.</li>
	<li>Una miscela di Li_2B_4O_7 e Li_2SO_4 per una rapida dissoluzione: una miscela di tetraborato di litio (Li_2B_4O_7) e solfato di litio (Li_2SO_4) in un rapporto di 2:1 in peso è evidenziata per la sua rapida capacità di sciogliere i silicati e gli ossidi refrattari.</li>
</ul>

I metodi di incenerimento a secco e di digestione a umido, sono comunemente utilizzati per decomporre materiali organici. Nell'incenerimento a secco, il campione organico viene riscaldato in un forno a muffola ad alta temperatura. Il calore provoca la combustione del materiale organico in presenza di ossigeno atmosferico, lasciando dietro di sé un residuo inorganico, o "cenere". Questa cenere può quindi essere disciolta in un solvente appropriato per ulteriori analisi. La digestione a umido comporta l'uso di acidi per scomporre il materiale organico.

Preparazione del campione per l'analisi: tecniche avanzate

L'analisi accurata di campioni complessi richiede spesso tecniche di preparazione avanzate per ottenere risultati affidabili e riproducibili. Campioni contenenti ...

sample-preparation-for-analysis-advanced-techniques

Education

Didattica

JoVE Core

Analytical Chemistry

Chimica Analitica

Unit 1

Unità 1

Method Development and Sampling Techniques

Sviluppo del Metodo e Tecniche di Campionamento

method-development-and-sampling-techniques

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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

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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

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sampling methods: sample types

Sampling Materials in Solid, Liquid, Gas

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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

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