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

Los métodos de preparación de muestras para el análisis inorgánico dependen de las propiedades del material.
Muchos materiales inorgánicos que son insolubles en agua se pueden solubilizar utilizando ácidos minerales fuertes. Si aún no se han disuelto, se utiliza un método más intensivo, conocido como técnica de fusión.
Aquí, la muestra se pesa y se mezcla con un material fundente en una proporción de aproximadamente 1 a 10 o 20. La mezcla de muestra y fundente se calienta en un crisol de platino para obtener una mezcla fundida. Al enfriarse, se solidifica para producir un nuevo material soluble en agua o ácido diluido.
Por el contrario, los materiales orgánicos se descomponen mediante métodos de incineración seca y digestión húmeda. En la ceniza seca, la muestra se calienta en un horno de mufla con oxígeno atmosférico. En este caso, la combustión del material orgánico genera un residuo inorgánico para su posterior análisis.
La digestión húmeda utiliza una mezcla de ácidos para descomponer el material orgánico.

preparación de muestras para análisis: técnicas avanzadas

El análisis preciso de muestras complejas a menudo requiere técnicas de preparación avanzadas para lograr resultados confiables y reproducibles. Las muestras que contienen materiales inorgánicos u orgánicos pueden ser difíciles de disolver o descomponer de manera efectiva. Los métodos estándar de preparación de muestras incluyen digestión ácida, fusión, incineración en seco y digestión húmeda.

La digestión ácida con ácidos fuertes se usa comúnmente para disolver materiales inorgánicos que son insolubles (no se disuelven) en agua. Este método puede ser útil para analizar muestras de suelo o minerales. Durante la digestión ácida, la muestra sólida insoluble se muele o tritura finamente para aumentar su área de superficie, lo que permite una reacción más efectiva con los ácidos. Los ácidos que se usan típicamente incluyen ácido clorhídrico, ácido nítrico, ácido sulfúrico y agua regia, una mezcla de ácido nítrico y clorhídrico. Cada ácido tiene ventajas específicas para diferentes tipos de muestras:
<ul style="padding-left: 35px;">
 <li style="list-style-type: disc; margin: 8px 0;">El ácido clorhídrico (HCl) se usa a menudo para disolver cloruros, óxidos y carbonatos y también es efectivo en materiales como metales y minerales.</li>
 <li style="list-style-type: disc; margin: 8px 0;">El ácido nítrico (HNO_3) es excelente para descomponer la materia orgánica y oxidar metales, lo que lo convierte en una opción común para el análisis de tejidos biológicos o metales.</li>
 <li style="list-style-type: disc; margin: 8px 0;">El ácido sulfúrico (H_2SO_4) se utiliza cuando se necesita un agente deshidratante fuerte, por ejemplo, para disolver muestras más resistentes como sulfuros o metales.</li>
 <li style="list-style-type: disc; margin: 8px 0;">El agua regia, una mezcla de ácidos nítrico y clorhídrico, es particularmente eficaz para disolver metales nobles como el oro y el platino, que son resistentes a los ácidos individuales.</li>
</ul>

La muestra se trata con el ácido de alta concentración elegido en un recipiente adecuado, donde se descompone en formas solubles o iones. También se puede aplicar calor para acelerar el proceso de digestión. Después de la digestión, la mezcla resultante diluida con agua es adecuada para un análisis posterior.

La técnica de fusión es un método alternativo para disolver materiales inorgánicos que no se pueden descomponer en una forma soluble mediante digestión ácida. Aquí, la muestra ponderada se mezcla con un material fundente en una proporción específica, típicamente de 1 a 10 o 20. La mezcla de muestra y fundente se coloca en un crisol de platino que es resistente a altas temperaturas y reacciones químicas. Este crisol se calienta en un horno de alta temperatura para obtener una mezcla fundida. Después del calentamiento, la mezcla fundida se deja enfriar hasta que produce un nuevo material soluble en agua o ácido diluido.
Varios ejemplos de uso de fundente en la preparación de muestras para disolver compuestos sólidos y líquidos son:
<ul style="padding-left: 35px;">
 <li style="list-style-type: disc; margin: 8px 0;">Na_2CO_3 y Na_2O_2 como fundentes para aleaciones de hierro y cromo: El carbonato de sodio (Na_2CO_3) es un fundente de uso común, pero se emplea peróxido de sodio (Na_2O_2) debido a su mayor capacidad oxidante en ciertos casos. Esta combinación es particularmente útil para disolver aleaciones de hierro y cromo en un crisol de níquel.</li>
 <li style="list-style-type: disc; margin: 8px 0;">Mezcla de Li_2B_4O_7 y Li_2SO_4 para disolución rápida: una mezcla de tetraborato de litio (Li_2B_4O_7) y sulfato de litio (Li_2SO_4) en una proporción de 2:1 en peso se destaca por su rápida capacidad para disolver silicatos y óxidos refractarios.	</li>
</ul>

Los métodos de incineración en seco y digestión húmeda se utilizan popularmente para descomponer materiales orgánicos. En la incineración en seco, la muestra orgánica se calienta en un horno de mufla a alta temperatura. El calor provoca la combustión del material orgánico en presencia de oxígeno atmosférico, dejando atrás un residuo inorgánico o "ceniza". Estas cenizas pueden disolverse en un disolvente adecuado para su posterior análisis. La digestión húmeda implica el uso de ácidos para descomponer la materia orgánica.

Preparación de muestras para análisis: técnicas avanzadas

El análisis preciso de muestras complejas a menudo requiere técnicas de preparación avanzadas para lograr resultados confiables y reproducibles. Muestras que contienen ...

sample-preparation-for-analysis-advanced-techniques

Education

Educación

JoVE Core

Analytical Chemistry

Química Analítica

Unit 1

Unidad 1

Method Development and Sampling Techniques

Desarrollo de Métodos y Técnicas de Muestreo

method-development-and-sampling-techniques

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

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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Quality Checks in Analytical Testing

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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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Choosing Samples for Reliable Results

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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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Sampling Errors in Sample Preparation

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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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