Quantitative Analysis

Quantitative analysis is a division of analytical chemistry that deals with the assaying the amount or percentage of one or more constituents of a sample. Quantitative analysis is important in chemistry for many reasons. Not only is it integral to the pursuit of pure science, but it has various practical applications, too. For example, it is used to measure nutrient levels and provides an accurate accounting of dosage, which is crucial to the formulation and testing of food and drugs. It is also used for medical diagnosis purpose, such as determining blood cholesterol levels or the ratio of lipoproteins in plasma or the amount of protein excreted in urine. In addition, quantitative tests are used to verify that products meet manufacturer or regulatory specifications. Such examples are too numerous to count. A variety of methods is employed for quantitative analysis, which can be broadly classified as chemical methods or instrumental methods (also known as physical methods). Chemical methods depend upon such reactions as precipitation, neutralization, oxidation, or, in general, the formation of a new compound. In contrast, instrumental methods allow us to apply measuring instruments that use the dependence of different physical properties to determine the concentration of the substance.

Chemical Methods Used in Quantitative Analysis

Chemical methods mainly include gravimetric analysis, titrimetric analysis (volumetric analysis) and combustion analysis.

  • Gravimetric analysis: A gravimetric analysis is one in which a sample is subjected to some treatment that causes a change in the physical state of the analyte that permits its separation from the other components of the sample. And then the weight of the separated substance is compared with the original sample substance to determine its content. Gravimetric method was the first technique used for quantitative chemical analysis, and it remains important tool in the modern chemistry laboratory.
  • Titrimetric analysis: Titrimetric analysis, otherwise known as volumetric analysis, determines the amount of some component in a sample by adding to the measured sample an exactly known quantity of another substance with which the desired constituent reacts in a definite, known proportion. The process is usually carried out by gradually adding a standard solution (i.e., a solution of known concentration) of titrating reagent, or titrant. Titrimetric analysis can be divided into four group: acid-base titration, redox titration, precipitation analysis and complexometry.
  • Combustion analysis: This analysis is primarily used to determine elemental composition of organic compounds (more precisely, empirical formula) by combusting the sample under conditions where the resulting combustion products can be quantitatively analyzed. You can then calculate the elemental composition by determining the number of moles of each combustion product.

Instrumental Methods Used in Quantitative Analysis

There are many instrumental methods used in quantitative analysis, some examples are as follows:

  • Ultraviolet-visible spectrophotometer: This is one of the instrumental optical methods that relies on the absorption of visible radiation by a solution of colored matter. When the absorbance of a particular solution is measured, the concentration of the solution can be calculated according to the formula of the Lambert-Beer law.
  • Chromatography: This is one of the most accurate quantitative analysis techniques. The peak height or area of the chromatography is proportional to the quantity of components in the solution, and the content of the measured substance in the sample can be accurately determined by applying a standard solution.
  • Inductively coupled plasma emission spectrometry (ICP-OES): ICP-OES is a technique for analyzing the concentration of metal elements in solid and liquid samples. It uses the principle of light emission from excited atoms to determine the element concentration.
  • Atomic Emission Spectroscopy (AES): This method relies on the optical emission of energized molecules. A sample substance is subjected to very high levels of energy and the energy forces the atoms to emit light, which is then analyzed and compared to elements or compounds with known light emission spectrum to determine the type and concentration of the constituent atoms.
  • A wide range of analytical chemicals for quantitative analysis such as gravimetric reagentstitration reagents (3S reagents for volumetric titration, indicators, karl fischer reagents and standards), chromatography standards, instrumental analytical reagents (chromatography reagents & solvents, mass spectrometry reagents, spectroscopy reagents, etc.), and many others.