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

Metody przygotowania próbek do analizy nieorganicznej zależą od właściwości materiału.
Wiele materiałów nieorganicznych, które są nierozpuszczalne w wodzie, można rozpuścić przy użyciu silnych kwasów mineralnych. Jeśli są one jeszcze nierozpuszczone, stosuje się bardziej intensywną metodę, znaną jako technika fuzji.
Tutaj próbka jest ważona i mieszana z materiałem topnikowym w stosunku około 1 do 10 lub 20. Mieszaninę próbki i topnika podgrzewa się w tyglu platynowym w celu uzyskania stopionej mieszaniny. Po schłodzeniu krzepnie, dając nowy materiał rozpuszczalny w wodzie lub rozcieńczonym kwasie.
Natomiast materiały organiczne są rozkładane metodami suchego popiołu i trawienia na mokro. W przypadku spopielania na sucho próbka jest podgrzewana w piecu muflowym z tlenem atmosferycznym. W tym przypadku spalanie materiału organicznego generuje pozostałość nieorganiczną do dalszej analizy.
Trawienie na mokro wykorzystuje mieszaninę kwasów do rozkładu materiału organicznego.

przygotowanie próbki do analizy: zaawansowane techniki

Dokładna analiza złożonych próbek często wymaga zaawansowanych technik przygotowania, aby uzyskać wiarygodne i powtarzalne wyniki. Próbki zawierające materiały nieorganiczne lub organiczne mogą być trudne do rozpuszczenia lub skutecznego rozkładu. Standardowe metody przygotowania próbek obejmują trawienie kwasem, stapianie, spopielanie na sucho i trawienie na mokro.

Trawienie kwasem przy użyciu mocnych kwasów jest powszechnie stosowane w celu rozpuszczenia materiałów nieorganicznych, które są nierozpuszczalne (nie rozpuszczają się) w wodzie. Ta metoda może być przydatna do analizy próbek gleby lub minerałów. Podczas trawienia kwasem nierozpuszczalna próbka stała jest drobno mielona lub kruszona w celu zwiększenia jej powierzchni, co umożliwia skuteczniejszą reakcję z kwasami. Typowo stosowane kwasy obejmują kwas solny, kwas azotowy, kwas siarkowy i wodę królewską – mieszaninę kwasu azotowego i kwasu solnego. Każdy kwas ma określone zalety dla różnych typów próbek:

<ul style="list-style-type: disc; display: flex; flex-direction: column; gap: 10px; padding: 0 0 0 40px;">
 <li>Kwas solny (HCl) jest często stosowany do rozpuszczania chlorków, tlenków i węglanów, a także jest skuteczny w przypadku materiałów takich jak metale i rudy.
 </li>
 <li>Kwas azotowy (HNO_3) doskonale nadaje się do rozkładania materii organicznej i utleniania metali, co czyni go powszechnym wyborem do analizy tkanek biologicznych lub metali.
 </li>
 <li>Kwas siarkowy (H_2SO_4) jest stosowany, gdy potrzebny jest silny środek odwadniający, na przykład do rozpuszczania bardziej odpornych próbek, takich jak siarczki lub metale.
 </li>
 <li>Woda królewska, mieszanina kwasu azotowego i solnego, jest szczególnie skuteczna w rozpuszczaniu metali szlachetnych, takich jak złoto i platyna, które są odporne na poszczególne kwasy.
 </li>
</ul>
Próbka jest traktowana wybranym kwasem o wysokiej mocy w odpowiednim pojemniku, gdzie jest rozkładana na formy rozpuszczalne lub jony. Można również zastosować ciepło, aby przyspieszyć proces trawienia. Po trawieniu otrzymana mieszanina rozcieńczona wodą nadaje się do dalszej analizy.

Technika fuzji jest alternatywną metodą rozpuszczania materiałów nieorganicznych, których nie można rozłożyć do postaci rozpuszczalnej przez trawienie kwasem. Tutaj ważona próbka jest mieszana z materiałem topnika w określonym stosunku, zwykle około 1 do 10 lub 20. Mieszanina próbki i topnika jest umieszczana w platynowym tyglu, który jest odporny na wysokie temperatury i reakcje chemiczne. Ten tygiel jest podgrzewany w piecu wysokotemperaturowym w celu uzyskania stopionej mieszanki. Po podgrzaniu stopionej mieszance pozwala się ostygnąć, aż powstanie nowy materiał rozpuszczalny w wodzie lub rozcieńczonym kwasie.

Kilka przykładów użycia topnika w przygotowaniu próbki do rozpuszczania związków stałych i ciekłych to:

<ul style="list-style-type: disc; display: flex; flex-direction: column; gap: 10px; padding: 0 0 0 40px;">
 <li>Na_2CO_3 i Na_2O_2 jako topniki do stopów żelaza i chromu: Węglan sodu (Na_2CO_3) jest powszechnie stosowanym topnikiem, ale w niektórych przypadkach stosuje się nadtlenek sodu (Na_2O_2) ze względu na jego silniejsze właściwości utleniające. Ta kombinacja jest szczególnie przydatna do rozpuszczania stopów żelaza i chromu w tyglu niklowym.
 </li>
 <li>Mieszanina Li_2B_4O_7 i Li_2SO_4 do szybkiego rozpuszczania: Mieszanina tetraboranu litu (Li_2B_4O_7) i siarczanu litu (Li_2SO_4) w stosunku wagowym 2:1 jest wyróżniona ze względu na jej szybką zdolność do rozpuszczania ogniotrwałych krzemianów i tlenków.
 </li>
</ul>
Metody suchego spopielania i mokrej trawienia są powszechnie stosowane do rozkładu materiałów organicznych. Podczas suchego spopielania próbka organiczna jest podgrzewana w piecu muflowym w wysokiej temperaturze. Ciepło powoduje spalanie materiału organicznego w obecności tlenu atmosferycznego, pozostawiając nieorganiczne pozostałości, czyli „popiół”. Popiół ten można następnie rozpuścić w odpowiednim rozpuszczalniku w celu dalszej analizy. Mokra trawienie obejmuje użycie kwasów do rozłożenia materiału organicznego.

Przygotowanie próbki do analizy: Zaawansowane techniki

Dokładna analiza złożonych próbek często wymaga zaawansowanych technik przygotowania w celu uzyskania wiarygodnych i powtarzalnych wyników. Próbki zawierające...

sample-preparation-for-analysis-advanced-techniques

Education

JoVE Core

Analytical Chemistry

Chemia analityczna

Unit 1

Jednostka 1

Method Development and Sampling Techniques

Opracowywanie metod i techniki pobierania próbek

method-development-and-sampling-techniques

KEY TERMS AND CONCEPTS

KLUCZOWE POJĘCIA I KONCEPCJE

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...

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Quality Control Charts and Lab Records

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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

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Calibrating Lab Glassware for Accurate Volume

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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

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

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