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

Os métodos de preparação de amostras para análise inorgânica dependem das propriedades do material.
Muitos materiais inorgânicos que são insolúveis em água podem ser solubilizados usando ácidos minerais fortes. Se ainda não estiverem dissolvidos, um método mais intensivo, conhecido como técnica de fusão, é usado.
Aqui, a amostra é pesada e misturada com um material de fluxo em uma proporção de cerca de 1 para 10 ou 20. A mistura amostra-fluxo é aquecida em um cadinho de platina para obter uma mistura fundida. No resfriamento, isso se solidifica para produzir um novo material solúvel em água ou ácido diluído.
Em contraste, os materiais orgânicos são decompostos por cinzas secas e métodos de digestão úmida. Na incineração a seco, a amostra é aquecida em mufla com oxigênio atmosférico. Aqui, a combustão do material orgânico gera um resíduo inorgânico para posterior análise.
A digestão úmida usa uma mistura de ácidos para quebrar o material orgânico.

preparação de amostras para análise: técnicas avançadas

A análise precisa de amostras complexas geralmente requer técnicas avançadas de preparação para a obtençao de resultados confiáveis ​​e reprodutíveis. Amostras contendo materiais inorgânicos ou orgânicos podem ser desafiadoras para se dissolver ou decompor efetivamente. Os métodos padrão de preparação de amostras incluem digestão ácida, fusão, incineração a seco e digestão úmida.

A digestão ácida com ácidos fortes é comumente utilizada para dissolver materiais inorgânicos que são insolúveis (não se dissolvem) em água. Este método pode ser útil para analisar amostras de solo ou minerais. Durante a digestão ácida, a amostra sólida insolúvel é finamente moída ou triturada para aumentar sua área de superfície, o que permite uma reação mais eficaz com os ácidos. Os ácidos normalmente usados ​​incluem ácido clorídrico, ácido nítrico, ácido sulfúrico e água régia – uma mistura de ácido nítrico e clorídrico. Cada ácido tem vantagens específicas para diferentes tipos de amostra:

<ul style="list-style-type: disc; display: flex; flex-direction: column; gap: 10px; padding: 0 0 0 40px;">
 <li>O ácido clorídrico (HCl) é frequentemente usado para dissolver cloretos, óxidos e carbonatos, e também é eficaz em materiais como metais e minérios.
 </li>
 <li>O ácido nítrico (HNO_3) é ​​excelente para quebrar matéria orgânica e oxidar metais, tornando-o uma escolha comum para tecidos biológicos ou análise de metais.
 </li>
 <li>O ácido sulfúrico (H_2SO_4) é usado quando um agente desidratante forte é necessário, por exemplo, para dissolver amostras mais resistentes, como sulfetos ou metais.
 </li>
 <li>A água régia, uma mistura de ácidos nítrico e clorídrico, é particularmente eficaz para dissolver metais nobres como ouro e platina, que são resistentes a ácidos individuais.
 </li>
</ul>
A amostra é tratada com o ácido de alta resistência escolhido em um recipiente adequado, onde é quebrada em formas solúveis ou íons. Calor também pode ser aplicado para acelerar o processo de digestão. Após a digestão, a mistura resultante diluída com água é adequada para uma análise posterior.

A técnica de fusão é um método alternativo para dissolver materiais inorgânicos que não podem ser quebrados em uma forma solúvel por digestão ácida. Nele, a amostra ponderada é misturada com um material de fluxo em uma proporção específica, normalmente cerca de 1 para 10 ou 20. A mistura amostra-fluxo é colocada em um cadinho de platina que é resistente a altas temperaturas e reações químicas. Este cadinho é aquecido em um forno de alta temperatura para a obtenção de uma mistura fundida. Após o aquecimento, a mistura fundida é deixada para esfriar até produzir um novo material solúvel em água ou ácido diluído.

Vários exemplos de uso de fluxo na preparação de amostras para dissolver compostos sólidos e líquidos são:

<ul style="list-style-type: disc; display: flex; flex-direction: column; gap: 10px; padding: 0 0 0 40px;">
 <li>Na_2CO_3 e Na_2O_2 como fluxos para ligas de ferro e cromo: carbonato de sódio (Na_2CO_3) é um fluxo comumente usado, mas o peróxido de sódio (Na_2O_2) é empregado devido à sua capacidade oxidante mais forte em certos casos. Esta combinação é particularmente útil para dissolver ligas de ferro e cromo em um cadinho de níquel.
 </li>
 <li>Mistura de Li_2B_4O_7 e Li_2SO_4 para Dissolução Rápida: Uma mistura de tetraborato de lítio (Li_2B_4O_7) e sulfato de lítio (Li_2SO_4) em uma proporção de 2:1 por peso merece destaque por sua capacidade de dissolver rapidamente silicatos e óxidos refratários.
 </li>
</ul>
Os métodos de incineração a seco e digestão úmida são popularmente utilizados ​​para decompor materiais orgânicos. Na incineração a seco, a amostra orgânica é aquecida em um forno mufla a uma temperatura alta. O calor causa a combustão do material orgânico na presença de oxigênio atmosférico, deixando para trás um resíduo inorgânico, ou "cinzas". Essas cinzas podem então ser dissolvidas em um solvente apropriado para análise posterior. A digestão úmida envolve o uso de ácidos para quebrar o material orgânico.

Preparação de Amostras para Análise: Técnicas Avançadas

A análise precisa de amostras complexas geralmente requer técnicas avançadas de preparação para obter resultados confiáveis e reprodutíveis. Amostras contendo ...

sample-preparation-for-analysis-advanced-techniques

Education

JoVE Core

Analytical Chemistry

Química Analítica

Unit 1

Unidade 1

Method Development and Sampling Techniques

Desenvolvimento de Métodos e Técnicas de Amostragem

method-development-and-sampling-techniques

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

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

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quantitative analysis

Measuring Analyte Concentration

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instrument calibration

Calibrating Lab Instruments for Accurate Results

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Calibrating Lab Glassware for Accurate Volume

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Preparing Standard Solutions in the Lab

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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...

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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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