What is analytical chemistry?

The analytical chemistry is the branch of chemistry that is dedicated to study or analyze (hence its name) the composition of the material . This means that it is in charge of determining what substances are made of, as well as in what proportion its components are found.

It is a purely experimental discipline that combines knowledge and skills from different areas ranging from statistics to modern physics and optics to develop analytical methods that allow determining, with an adequate level of confidence, what a sample contains.

In addition to its importance in basic scientific research , this branch of chemistry is applied in practically all industries. This is because it allows monitoring from the quality of a chemical or food product, to the levels of pollutants present in the wastes that are being discharged into the environment.

Brief history of analytical chemistry

The origins of analytical chemistry can be traced to the work of Antoine Lavoisier at the end of the 18th century, who carried out important studies related to the composition of minerals and air, as well as the combustion process and animal respiration.

Mohr did more than just publish his discoveries. He also invented volumetric techniques and designed and built some of the most important volumetric analysis instruments in analytical chemistry, such as the volumetric pipettes and the burette.

Additionally, in his laboratory in Frankfurt, he trained many other apprentices in the techniques that he himself developed. In addition to quantitative techniques such as volumetry and gravimetry, he also taught them qualitative techniques of chemical analysis. For this and much more, he is considered the father of analytical chemistry.

Branches of analytical chemistry

Analytical chemistry can be roughly divided into two classes, depending on the purpose of the chemical analysis:

Qualitative analytical chemistry

The first problem analytical chemistry seeks to solve is determining what is in an unknown sample. That is, find or identify what its components are. This type of analysis is called qualitative analysis, so this branch of analytical chemistry is also called qualitative analytical chemistry.

Quantitative analytical chemistry

This branch of analytical chemistry is responsible for determining how much of each component is in a sample. That is, it seeks to measure in what quantity, proportion or concentration are the different components, which are called analytes .

This is why, except on a few occasions when it is known in advance what is being analyzed, qualitative and quantitative analytical chemistry always go hand in hand.

Analytical methods

Analytical chemistry uses both qualitative and quantitative methods to understand the composition of matter:

1. Qualitative methods

Qualitative methods are based on chemical reactions such as precipitation and complex formation, as well as the use of separation techniques to identify the components of a sample. These are classic methods and include the following examples:

  • Cationic analytical runs : systematic set of chemical tests that allows to identify the presence of certain metallic cations.
  • Anion Analytical Runs: A systematic set of chemical tests that confirms the presence of certain common anions.
  • Flame tests: A simple test that identifies some metals based on the color of the flame when the sample is burned.

2. Quantitative methods

These consist of determining the concentration of a species in a sample. Analytical methods are generally divided into classical wet techniques such as volumetry and gravimetry, and modern instrumental techniques such as spectrometric techniques and chromatography, which will be explained below:

  • Volumetric analysis methods

Volumetry refers to a set of techniques for the indirect determination of the concentration of an analyte in a sample or in an aliquot thereof, based on the measurement of the volume of a reagent of known concentration that is necessary to consume the analyte stoichiometrically. These techniques are also called qualifications or evaluations.

All volumetric methods are based on finding the equivalence point, in which it is true that:

Since the equivalents are equal to the normal concentration by volume, and the concentration of the titrant is known, then measuring its volume implies that the number of equivalents of the titrant, and therefore of the analyte or titrant, will be known, as shown below. continuation:

There are many analytical methods based on volumetry, which differ according to the type of chemical reaction they use. Based on this, the following types of volumetric methods can be distinguished:

    • Acid-base volumetry: in these cases, either the analyte is an acid and the titrant a base, or the opposite. The reaction is an acid-base neutralization and the end point of the titration is determined by the color change of a chemical indicator.
    • Precipitation volumetry: in this technique the reaction involved is the formation of an insoluble precipitate.
    • Titration or volumetry of complex formation: in this case, the reaction is the formation of a metallic complex, sometimes colored, sometimes not.
    • Redox volumetry : refers to the volumetry that involves an oxidation and reduction reaction between the titrant and the analyte. One acts as an oxidizing agent and the other as a reducing agent.
  • Gravimetric analysis methods

Unlike the previous case, these methods are based on the measurement of the mass or the change in the mass of a sample after being subjected to different types of both chemical and thermal treatments.

Some examples of common gravimetric methods in the analytical chemistry laboratory are:

    • Precipitation methods: In these cases, the analyte is usually an ion that precipitates quantitatively as an insoluble salt. This salt is filtered and dried to later determine its mass. With this mass, the amount of analyte that was in the original sample is then determined.
    • Volatilization methods: unlike the previous one, the analyte in this case separates from the sample matrix in the form of a gas. In some methods, this gas is collected by reacting it with a suitable reagent and then weighing the product of said reaction. In others, the mass of the gas is determined by the difference in weight before and after volatilization.
    • Electrodeposition: is similar to precipitation methods, except that the analyte is deposited on an electrode due to a redox reaction generated by an electric current. Increasing the mass of the electrode allows the amount of analyte in the sample to be determined.
  • Instrumental methods

Modern analytical methods are largely based on the use of advanced scientific instruments that are capable of analyzing complex samples efficiently, accurately, and in some cases automated. These methods are based on the measurement of some physical property that can be correlated with the concentration of the analyte in the sample.

Some techniques measure differences in electrical potential or current intensities, while others measure the amount of light emitted or absorbed by atoms or molecules at specific wavelengths. Some examples of instrumental analytical methods are:

    • Spectrometric methods: these methods are based on the phenomenon of light absorption by atoms and molecules, or on the emission of light when atoms are heated to high temperatures. In the first case, the techniques are called absorption spectrometry (atomic or molecular as the case may be) and in the second they are called atomic emission spectrometry.
    • Electroanalytical methods: unlike the previous ones, these measure changes in electricity or electrical properties of a sample in the presence of the analyte. This includes measurements of current intensity (as in the case of polarography), voltage (as in the case of pH meters), electrical conductivity, etc.
  • Chromatographic methods

Chromatography can be thought of as a separate class of separate analytical method, as it includes separation, qualitative identification and quantification all in one. These methods can be combined with volumetric or instrumental techniques for the analysis of the separated analytes.

In this technique, a complex sample is dissolved in a suitable solvent and flowed through a porous material such as a gel, filter paper or fine sand, pushed by the same solvent.

The different solutes present in the sample will have different affinities for the porous material so some will move through it faster than others. At the end, the resulting fractions are collected for analysis, or they are analyzed online by means of an absorption spectrometer.

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