analytic chemistry



We explain what analytical chemistry is and what this branch of chemistry focuses on. Also, the analytical methods you use.

Analytical chemistry uses different analytical methods.

What is analytical chemistry?

Analytical chemistry is called a branch of the chemistry that focuses on understanding the matter, that is, of the analysis of the materials that make up a sample, using experimental or laboratory methods.

Analytical chemistry can be classified into quantitative and qualitative analytical chemistry. Quantitative analytical chemistry is used to determine the amount, concentration, or proportion of one or more components in a sample, that is, it deals with quantifying matter.

Qualitative analytical chemistry is used to know what the components of a sample are, that is, it is concerned with identifying each component of the sample. On the other hand, analytical chemistry is also used for the separation of the components of a sample. Generally, the substance in question (the one to be identified or quantified) is called an analyte.

The knowledge that gave rise to analytical chemistry arose from the modern idea of ​​the chemical composition of matter, which emerged in the 18th century.

An important milestone in the development of this discipline It was the understanding of the correlation between the physical properties of matter and its chemical composition. In this, the study of spectroscopy, electrochemistry and polarography were fundamental.

However, the invention of methods of chemical analysis that would allow the fuller understanding of matter would advance along with scientific and technological development, so that the general characteristics of the field of analytical chemistry would only be defined in the twentieth century.

Analytical chemistry uses the following analytical methods to understand matter:

Quantitative methods

  • Volumetric methods. Known as titration or titration, they are quantitative methods in which a reagent whose concentration is known (titrant substance) is used to determine that of another reagent whose concentration is unknown (analyte or substance to be analyzed in the sample), by means of a chemical reaction In titrations, generally, indicators are used that mark the end point of the reaction. There are different types of degrees:
    • Acid-base titrations. They are those in which a acid with a base using an acid-base indicator. In general, the base is placed in a burette (a chemical container used to measure volumes) and a flask is placed in an Erlenmeyer flask. volume known acid with a few drops of phenolphthalein (indicator) added. Phenolphthalein turns pink in a basic medium and is colorless in an acid medium. Then the method consists of adding the base to the acid until the final solution turns pink, which means that the reaction between the acid and the base has reached its end point. An instant before reaching the end point, the reaction reaches its equivalence point, which is where the amount of substance in the titrant is equal to the amount of substance in the analyte. If the stoichiometry in the reaction is 1: 1, that is, the same amount of analyte substance reacts as the titrant, the following equation can be used to determine the amount of analyte:


    • [X] is the known concentration of the substance X, expressed mol / L or equivalent units.
    • V (X) is the volume of the substance X dispensed from the burette, expressed in L or equivalent units.
    • [Y] is the unknown concentration of the analyte Y, expressed in mol / L or equivalent units.
    • V (Y) is the volume of the substance Y contained in the Erlenmeyer flask, expressed in L or equivalent units.

It is important to clarify that, although this equation is widely used, it often varies depending on the type of degree used.

    • Redox titrations. The basis is the same as in acid-base titrations, but in this case there is a redox reaction between the analyte and a dissolution oxidizing or reducing, as the case may be. The indicator used can be a potentiometer (equipment to measure potential difference) or a redox indicator (compounds that have a defined color in each of their oxidation states).
    • Complex formation qualifications. They consist of the complex formation reaction between the analyte and the titrant.
    • Precipitation titrations. They consist of the formation of a precipitate. They are very specific and the indicators used are very particular to each reaction.
  • Gravimetric methods. Quantitative method which consists of measuring the weight of a material or substance before and after making any changes. The instrument to perform the measurement it is generally an analytical balance. There are several gravimetric methods:
    • Precipitation. It consists of the formation of a precipitate, so that when it is weighed, its quantity in the original sample can be calculated using stoichiometric relationships. The precipitate can be collected from the solution in which it is found by filtration. To apply this method, the analyte must be poorly soluble and chemically well defined.
    • Volatilization. It consists of volatilizing the analyte to separate it from the sample. Then the analyte is recovered by its absorption in some material, this material is weighed, and the gain of weight It will be due to the incorporation of the analyte, whose weight will be calculated by the difference in weights of the absorbent material before and after having absorbed the analyte. This method can only be applied when the analyte is the only volatile substance in the sample.
    • Electrodeposition. It consists of a redox reaction where the analyte is deposited on an electrode as part of a compound. The electrode is then weighed before and after the redox reaction, in this way the amount of analyte deposited can be calculated.

More advanced instrumental methods:

  • Spectrometric methods. Apparatus are used to measure the behavior of electromagnetic radiation (light) in contact with the substance or compound under analysis.
  • Electroanalytical methods. Similar to the spectrometric, but the electricity instead of light to measure electrical potential or electric current transmitted by the substance to be analyzed.
  • Chromatographic methods. The chromatography is a method of separation, characterization and quantification of complex mixtures. It is used to separate one or more components of a mixture and at the same time identify them and calculate their concentration or quantity in the sample, that is, quantify them. The chromatographic method basically consists of a stationary phase and a mobile phase that are part of an equipment or structure that is used to analyze the sample. The stationary phase is immobile and consists of a substance that adheres to some system generally designed in the form of a column and the mobile phase is a substance (liquid or gaseous) that flows through the stationary phase. The separation of the components (analytes) occurs according to the affinity of each of them for the stationary phase or for the mobile phase, which will depend on various chemical and physical properties (of each one or of both phases). There are different types of chromatography depending on the substances used as the mobile and stationary phase, the conditions imposed on the method and the designs of the chromatographic equipment. For example, in the following image you can see the separation of the different components of a mixture that was injected on a chromatographic column. You can see the different colors of each component as they descend through the stationary phase that fills the column:

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