ANALYTE: QUALITATIVE AND QUANTITATIVE ANALYSIS, STEPS - CHEMISTRY - 2025

The analyte is a chemical species (ions, molecules, polymeric aggregates), whose presence or concentration is desired to know in a chemical measurement process. When talking about the measurement process, it refers to any of the existing analytical techniques, whether classical or instrumental.

To study the analyte, a "chemical magnifying glass" is needed to allow its visualization in order to identify it within the environment that surrounds it; this medium is known as the matrix. Also, a rule is needed, which is built from standards with known concentration and response values ​​(absorbances, voltage, current, heat, etc.).

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The classical techniques to determine or quantify the analyte usually consist in making it react with another substance whose composition and concentration are exactly known. This is a comparison with a standard unit (known as a titrant) in order to determine the purity of the analyte through it.

While the instrumental, although they may have the same classical principle, they seek to relate a physical response to the concentration of the analyte. Among these techniques we can mention globally: spectroscopy, calorimetry, voltammetry and chromatography.

Qualitative and quantitative analysis of the analyte

Qualitative analysis is about the identification of the elements or substances present in a sample through a set of specific reactions. And quantitative analysis seeks to determine how much of a particular substance is present in a sample.

The determined substance is often called the desired component or analyte, and it can constitute a small or large part of the sample studied or analyzed.

If the analyte is more than 1% of the sample, it is considered to be a major component; while if it constitutes between 0.01 to 1%, it is considered a minor component of the sample. And if the substance represents less than 0.01% of the sample, the analyte is considered to be a trace component.

The quantitative analysis can be based on the size of the sample taken, and the analyzes can generally be divided as follows:

-Macro, when the weight of the sample is greater than 0.1 g

-Semimicro, with samples between 10 to 100 mg

-Micro, with samples from 1 to 10 mg

-Ultramicro, they are related to the use of samples of the order of micrograms (1 μg = 10 ^-6 g)

Steps in quantitative analysis

A quantitative analysis of a sample consists of four stages:

-Sampling

-Convert the analyte in a suitable form for its measurement

-Measurement

-Calculation and interpretation of measurements.

Analyte sampling

The selected sample must be representative of the material from which it was extracted. This implies that the material must be as homogeneous as possible. Therefore, the composition of the sample should reflect that of the material from which it was taken.

If the sample is selected with due care, the concentration of the analyte found in it will be that of the material under study.

The sample consists of two parts: the analyte and the matrix in which the analyte is immersed. It is desirable that the methodology used for the analysis eliminates as much as possible the interference of the substances contained in the matrix.

The material in which the analyte is going to be studied can be of different natures; for example: a liquid, a portion of a rock, a portion of a soil, a gas, a sample of blood or other tissue, etc. So the method for taking a sample may vary depending on the nature of the material.

If a liquid is to be analyzed, the complexity of the sampling will depend on whether the liquid is homogeneous or heterogeneous. Likewise, the method of taking a sample of a liquid depends on the objectives that are intended to be developed in the study.

Transformation of the analyte into a measurable form

The first step in this phase of using the quantitative analytical method is the dissolution of the sample. The method used for this purpose varies with the nature of the material under study.

Although each material can present a specific problem, the two most common methods used to dissolve samples are:

-Treatment with strong acids, such as sulfuric, hydrochloric, nitric or perchloric acids

-Melting in an acidic or basic flux, followed by a treatment with water or an acid.

Before making the determination of the concentration of the analyte in the sample, the problem of interferences must be solved. These can be produced by substances that respond positively to the reagents used in the analyte determination, which can cause false results.

Also the interference can be of such magnitude that it prevents the reaction of the analyte with the reagents used in its determination. Interferences can be eliminated by altering their chemical nature.

The analyte is also separated from the interference by precipitation of the interference, using the specific reagents for each case.

Measurement

This step can be carried out by physical or chemical methods, in which specific or selective reactions are carried out for the analyte. At the same time, standard solutions are processed in the same way, allowing for the determination of the analyte concentration by comparison.

In many cases, it is necessary to use instrumental techniques designed to solve problems in the chemical analysis of substances, such as: absorption spectroscopy, flame photometry, gravimetry, etc. The use of these techniques allows the identification of the presence of the analyte in the sample and its quantification.

In the course of the quantitative instrumental analysis, solutions of known concentration (standards or standards) must be prepared to which the response is determined in the application of the method to construct a calibration curve (which serves as a "chemical rule")..

It is important to design and use suitable blanks that can provide information on possible errors in the analysis, and on the minimum amount of analyte that can be determined with the method used.

The blanks provide information about the quality of the reagents and the applied methodology.

Calculation and interpretation of measurements

Once the results are obtained, they proceed to their statistical analysis.

Initially, the mean of the results is calculated, as well as the standard deviation using the appropriate methodology. Subsequently, the error of the application of the method is calculated, and by comparing it with the statistical tables, it is determined if the error made in obtaining the results of the analyte concentration falls within the allowed limits.

References

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2. Chapter 3: The Vocabulary of Analytical Chemistry.. Recovered from: agora.cs.wcu.edu
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5. Denton R. Braun. (April 1, 2016). Chemical analysis. Encyclopædia Britannica. Recovered from: britannica.com