In chemistry,
quantitative analysis is the determination of the absolute or relative abundance (often expressed as a
concentrationIn chemistry, concentration is the measure of how much of a given substance there is mixed with another substance. This can apply to any sort of chemical mixture, but most frequently the concept is limited to homogeneous solutions, where it refers to the amount of solute in the solvent.To...
) of one, several or all particular
substance(s)A chemical substance is a material with a specific chemical composition.A common example of a chemical substance is pure water; it has the same properties and the same ratio of hydrogen to oxygen whether it is isolated from a river or made in a laboratory. Some typical chemical substances are...
present in a sample.
Once the presence of certain substance(s) in a sample is known, the study of their absolute or relative abundance can help in determining specific properties. Knowing the composition of a sample is very important and several ways have been developed to make it possible, like gravimetric and volumetric analysis.
In chemistry,
quantitative analysis is the determination of the absolute or relative abundance (often expressed as a
concentrationIn chemistry, concentration is the measure of how much of a given substance there is mixed with another substance. This can apply to any sort of chemical mixture, but most frequently the concept is limited to homogeneous solutions, where it refers to the amount of solute in the solvent.To...
) of one, several or all particular
substance(s)A chemical substance is a material with a specific chemical composition.A common example of a chemical substance is pure water; it has the same properties and the same ratio of hydrogen to oxygen whether it is isolated from a river or made in a laboratory. Some typical chemical substances are...
present in a sample.
Once the presence of certain substance(s) in a sample is known, the study of their absolute or relative abundance can help in determining specific properties. Knowing the composition of a sample is very important and several ways have been developed to make it possible, like gravimetric and volumetric analysis. Gravimetric analysis yields more accurate data about the composition of a sample than volumetric analysis does, but the first one takes more time to perform in the laboratory and is a little boring. Volumetric analysis in the other side doesn't take that much time and the results that we obtain are in the most cases satisfactory. Volumetric analysis can be simply a
titrationTitration is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of a known reactant...
based in a
neutralizationIn chemistry, neutralization, or neutralisation is a chemical reaction whereby an acid and a base react to form water and a salt....
reaction but it can also be a
precipitationPrecipitation may refer to:* Precipitation , rain, sleet, hail, snow and other forms of water falling from the sky* Precipitation , the condensation of a solid from a solution during a chemical reaction...
or a
complexThis article is about the meaning of complex as it pertains to science and mathematics. For information on Complex magazine, see Complex magazine....
forming reaction as well as a titration based in an
redoxRedox describes all chemical reactions in which atoms have their oxidation number changed....
reaction. However, each method in quantitative analysis has a general specification, in neutralization reactions, for example, the reaction that occurs is between an acid and a base, which yields a salt and water, hence the name neutralization. In the precipitation reactions the
standard solution Standard solution is a chemical term which describes a solution of known concentration. The concentration of the solution is normally expressed in units of moles per Liter...
is in the most cases
silver nitrateSilver nitrate, also known as lunar caustic, is a soluble chemical compound with chemical formula AgNO
3. This compound is a versatile precursor to many other silver compounds, such as those used in photography. Comparatively, it is far less sensitive to light than the halides...
which is used as a reagent to react with the ions present in the sample and to form a high insoluble precipitate. Precipitation methods are often called simply as
ArgentometryIn analytical chemistry, argentometry is a type of titration involving the silver ion. Typically, it is used to determine the amount of chloride present in a sample. The sample solution is titrated against a solution of silver nitrate of known concentration...
. In the two other methods the situation is the same. Complex forming titration is a reaction that occurs between metal ions and a standard solution that is in the most cases EDTA (ethylene diamine tetra acetic acid). In the redox titration that reaction is carried out between an
oxidizing agentAn oxidizing agent can be defined as either:#a chemical compound that readily transfers oxygen atoms, or#a substance that gains electrons in a redox chemical reaction...
and a reduction agent.
For example, quantitative analysis performed by
mass spectrometryMass spectrometry is an analytical technique for the determination of the elemental composition of a sample or molecule. It is also used for elucidating the chemical structures of molecules, such as peptides and other chemical compounds...
on biological samples can determine, by the relative abundance ratio of specific
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
s, indications of certain diseases, like cancer.
Quantitative vs. Qualitative
The term "quantitative analysis" is often used in comparison (or contrast) with "qualitative analysis", which seeks information about the identity or form of substance present. For instance, a chemist might be given an unknown solid sample. He or she will use "qualitative" techniques (perhaps
NMRNuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is the name given to a technique which exploits the magnetic properties of certain nuclei. This phenomenon and its origins are detailed in a separate section on nuclear magnetic resonance. The most important...
or IR spectroscopy) to identify the compounds present, and then quantitative techniques to determine the amount of each compound in the sample. Careful procedures for recognizing the presence of different metal ions have been developed, although they have largely been replaced by modern instruments; these are collectively known as
qualitative inorganic analysisClassical qualitative inorganic analysis is a method of analytical chemistry which seeks to find elemental composition of inorganic compounds. It is mainly focused on detecting ions in an aqueous solution, so that materials in other forms may need to be brought into this state before using standard...
. Similar tests for identifying organic compounds (by testing for different
functional groupIn organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part...
s) are also known.
Many techniques can be used for either qualitative or quantitative measurements. For instance, suppose an
indicatorIndicator may mean:* Indicator , a genus of birds in the honeyguide family* In chemistry:** pH indicator, a chemical detector for protons in acid-base titrations** Redox indicator, a chemical detector for redox titrations...
solution changes color in the presence of a metal ion. It could be used as a qualitative test: does the indicator solution change color when a drop of sample is added? It could also be used as a quantitative test, by studying the colour of the indicator solution with different concentrations of the metal ion. (This would probably be done using
ultraviolet-visible spectroscopyUltraviolet-visible spectroscopy or ultraviolet-visible spectrophotometry involves the spectroscopy of photons in the UV-visible region. This means it uses light in the visible and adjacent ranges. The absorption in the visible ranges directly affects the color of the chemicals involved...
.)